773 33.Exoskeletons for Human Performance Augmentation Homayoon Kazerooni Although autonomous robotic systems perform 33.1 Survey of Exoskeleton Systems.............. 773 remarkably in structured environments(e.g.,fac- 33.2 Upper-Extremity Exoskeleton................775 tories),integrated human-robotic systems are 33.3 Intelligent Assist Device....................... 776 superior to any autonomous robotic systems in un- structured environments that demand significant 33.4 Control Architecture for Upper-Extremity 778 adaptation.The technology associated with exo- Exoskeleton Augmentation................. skeleton systems and human power augmentation 33.5 Applications of Intelligent Assist Device..780 can be divided into lower-extremity exoskeletons 33.6 Lower-Extremity Exoskeleton 780 and upper-extremity exoskeletons.The reason for this was twofold;firstly,one could envision a great 33.7 The Control Scheme of an Exoskeleton....782 many applications for either a stand-alone lower- 33.8 Highlights of the Lower-Extremity Design 786 or upper-extremity exoskeleton in the immedi- 33.9 Field-Ready Exoskeleton Systems...........790 ate future.Secondly,and more importantly for the 33.9.1 The ExoHiker Exoskeleton............. 790 division,is that these exoskeletons are in their 33.9.2 The ExoClimber Exoskeleton........... 790 early stages,and further research still needs to be conducted to ensure that the upper-extremity 33.10 Conclusion and Further Reading 792 exoskeleton and lower-extremity exoskeleton can References.… 792 function well independently before one can ven- ture an attempt to integrate them.This chapter first gives a description of the upper-extremity more detailed description of the lower-extremity exoskeleton efforts and then will proceed with the exoskeleton. 33.1 Survey of Exoskeleton Systems In the early 1960s,the US Defense Department ex- The outer exoskeleton (the slave)followed the motions pressed interest in the development of a man-amplifier,of the inner exoskeleton (the master),which followed a powered suit of armor which would augment sol- the motions of the human operator.All these studies diers'lifting and carrying capabilities.In 1962,the Air found that duplicating all human motions and using Force had the Cornell Aeronautical Laboratory study master-slave systems were not practical.Additionally. the feasibility of using a master-slave robotic system as difficulties in human sensing and system complexity a man-amplifier.In later work,Cornell determined that kept it from walking. an exoskeleton,an external structure in the shape of the Vukobratovic et al.developed a few active orthoses human body which has far fewer degrees of freedom than for paraplegics [33.7].The systems include hydraulic or a human,could accomplish most desired tasks [33.1].pneumatic actuators for driving the hip and knee joints in Part From 1960 to 1971,General Electric developed and the sagittal plane.These orthoses were coupled with the tested a prototype man-amplifier,a master-slave system wearer via shoe bindings,cuffs,and a corset.The device called the Hardiman [33.2-6].The Hardiman was a set was externally powered and controlled via a predeter- of overlapping exoskeletons worn by a human operator. mined periodic motion.Although these early devices
773 Exoskeletons 33. Exoskeletons for Human Performance Augmentation Homayoon Kazerooni Although autonomous robotic systems perform remarkably in structured environments (e.g., factories), integrated human–robotic systems are superior to any autonomous robotic systems in unstructured environments that demand significant adaptation. The technology associated with exoskeleton systems and human power augmentation can be divided into lower-extremity exoskeletons and upper-extremity exoskeletons. The reason for this was twofold; firstly, one could envision a great many applications for either a stand-alone loweror upper-extremity exoskeleton in the immediate future. Secondly, and more importantly for the division, is that these exoskeletons are in their early stages, and further research still needs to be conducted to ensure that the upper-extremity exoskeleton and lower-extremity exoskeleton can function well independently before one can venture an attempt to integrate them. This chapter first gives a description of the upper-extremity exoskeleton efforts and then will proceed with the 33.1 Survey of Exoskeleton Systems ............... 773 33.2 Upper-Extremity Exoskeleton ................ 775 33.3 Intelligent Assist Device ........................ 776 33.4 Control Architecture for Upper-Extremity Exoskeleton Augmentation.................... 778 33.5 Applications of Intelligent Assist Device .. 780 33.6 Lower-Extremity Exoskeleton ................ 780 33.7 The Control Scheme of an Exoskeleton.... 782 33.8 Highlights of the Lower-Extremity Design 786 33.9 Field-Ready Exoskeleton Systems ........... 790 33.9.1 The ExoHiker Exoskeleton.............. 790 33.9.2 The ExoClimber Exoskeleton........... 790 33.10 Conclusion and Further Reading ............ 792 References .................................................. 792 more detailed description of the lower-extremity exoskeleton. 33.1 Survey of Exoskeleton Systems In the early 1960s, the US Defense Department expressed interest in the development of a man-amplifier, a powered suit of armor which would augment soldiers’ lifting and carrying capabilities. In 1962, the Air Force had the Cornell Aeronautical Laboratory study the feasibility of using a master–slave robotic system as a man-amplifier. In later work, Cornell determined that an exoskeleton, an external structure in the shape of the human body which has far fewer degrees of freedom than a human, could accomplish most desired tasks [33.1]. From 1960 to 1971, General Electric developed and tested a prototype man-amplifier, a master–slave system called the Hardiman [33.2–6]. The Hardiman was a set of overlapping exoskeletons worn by a human operator. The outer exoskeleton (the slave) followed the motions of the inner exoskeleton (the master), which followed the motions of the human operator. All these studies found that duplicating all human motions and using master–slave systems were not practical. Additionally, difficulties in human sensing and system complexity kept it from walking. Vukobratovic et al. developed a few active orthoses for paraplegics [33.7]. The systems include hydraulic or pneumatic actuators for driving the hip and knee joints in the sagittal plane. These orthoses were coupled with the wearer via shoe bindings, cuffs, and a corset. The device was externally powered and controlled via a predetermined periodic motion. Although these early devices Part D 33
774 Part D Manipulation and Interfaces were limited to predefined motions and had limited suc-joint trajectories without the use of any sensory systems cess,balancing algorithms developed for them are still from its wearer. used in many bipedal robots [33.8]. The hybrid assisted limb(HAL)was developed at the Seireg et al.also created an exoskeleton system for University of Tsukuba ([33.13,141).This 15 kg battery- paraplegics where only the hip and knee were pow- powered suit detects muscle myoelectrical signals on ered by hydraulic actuators in sagittal plane [33.9]. the skin surface below the hip and above the knee.The The hydraulic power unit consists of a battery-powered signals are picked up by the sensors and sent to the direct-current (DC)motor,pump,and accumulator.computer,which translates the nerve signals into sig- A bank of servo-valves drives the actuators at the knee nals of its own for controlling electric motors at the and hip.The device was controlled to follow a set of hips and knees of the exoskeleton,effectively amplify- a Fig.33.1 (a)Hardiman;(b)An exoskeleton system designed for paraplegics by Seireg et al.[33.9]:(c)HAL Part D33.1 Fig.33.2 (a)An exoskeleton for patient handling [33.10,11];(b)RoboKnee [33.12]
774 Part D Manipulation and Interfaces were limited to predefined motions and had limited success, balancing algorithms developed for them are still used in many bipedal robots [33.8]. Seireg et al. also created an exoskeleton system for paraplegics where only the hip and knee were powered by hydraulic actuators in sagittal plane [33.9]. The hydraulic power unit consists of a battery-powered direct-current (DC) motor, pump, and accumulator. A bank of servo-valves drives the actuators at the knee and hip. The device was controlled to follow a set of a) b) c) Fig. 33.1 (a) Hardiman; (b) An exoskeleton system designed for paraplegics by Seireg et al. [33.9]; (c) HAL a) b) Fig. 33.2 (a) An exoskeleton for patient handling [33.10, 11]; (b) RoboKnee [33.12] joint trajectories without the use of any sensory systems from its wearer. The hybrid assisted limb (HAL) was developed at the University of Tsukuba ([33.13,14]). This 15 kg batterypowered suit detects muscle myoelectrical signals on the skin surface below the hip and above the knee. The signals are picked up by the sensors and sent to the computer, which translates the nerve signals into signals of its own for controlling electric motors at the hips and knees of the exoskeleton, effectively amplifyPart D 33.1
Exoskeletons for Human Performance Augmentation 33.2 Upper-Extremity Exoskeleton 775 ing muscle strength.In addition to electromyography tor coupling the upper and the lower portions of a knee (EMG)signals,the device further includes potentiome-brace.The control of this powered knee brace requires ters for measuring the joint angles,force sensors for the ground reaction force measured by two load cells. measuring the ground reaction forces and a gyroscope The system uses a positive-feedback force controller to and accelerometer for measuring the torso angle.Each create an appropriate force for the actuator. leg of HAL powers the flexion/extension motion at the Kong et al.developed a full lower-limb exoskeleton hip and knee in the sagittal plane through the use of system that works with a powered walker [33.15].The DC motors integrated with harmonic drives.The ankle walker houses the electric actuators,the controller,and includes passive degrees of freedom. the batteries,reducing the weight of the exoskeleton Yamamoto et al.[33.10,11]have created an exoskel- system.A transmission system transmits power to the eton system for assisting nurses during patient handling. wearer's joints from the actuators in the walker.The The lower limbs include pneumatic actuators for the exoskeleton is powered at the hips and knees in sagittal flexion/extension of the hips and knees in the sagittal plane.The input to drive the system is a set of pressure plane.Air pumps are mounted directly onto each actua-sensor that measure the force applied by the quadriceps tor to provide pneumatic power.User input is determined muscle on the knee. via force sensing resistors coupled to the wearer's skin. Agrawal et al.have conducted research projects on The measurement from force sensing resistor (FSR)statically balanced leg orthoses that allow for less effort and other information such as joint angles are used to during swing [33.16].In the passive version,the device determine the required input torques for various joints.uses springs in order to cancel the gravity force associ- Pratt et al.developed a powered knee brace for ated with the device links and the person leg.Through adding power at the knee to assist in squatting [33.12]. experiments the authors showed that the device reduced The device is powered by a linear series-elastic actua- the required torque by the wearer substantially. 33.2 Upper-Extremity Exoskeleton In the mid-1980s,researchers at Berkeley initiated sev- movements accordingly,but the force he/she feels is eral research projects on upper-extremity exoskeleton much smaller than what he/she would feel without the systems,billed as human extenders [33.17-23].The device.In another example,suppose the worker uses main function of an upper-extremity exoskeleton is the device to maneuver a large,rigid,and bulky ob- human power augmentation for the manipulation of ject,such as an exhaust pipe.The device will convey heavy and bulky objects.Since upper-extremity ex- the force to the worker as if it was a light,single- oskeletons are mostly used for factory floors,warehouse, point mass.This limits the cross-coupled and centrifugal and distribution centers,they are hung from overhead forces that increase the difficulty of maneuvering a rigid cranes.As can be seen in later sections,lower-extremity body and can sometimes produce injurious forces on exoskeletons focus on supporting and carrying heavy the wrist.In a third example,suppose a worker uses payloads on the operator's back(like a backpack)during the device to handle a powered torque wrench.The de- long-distance locomotion.Upper-extremity exoskele-vice will decrease and filter the forces transferred from tons,which are also known as assist devices or human the wrench to the worker's arm so the worker feels the power extenders,can simulate forces on a worker's low-frequency components of the wrench's vibratory arms and torso.These forces differ from,and are usu-forces instead of the high-frequency components that ally much smaller than the forces needed to maneuver produce fatigue [33.24].These assist devices not only a load.When a worker uses an upper-extremity exoskel- filter out unwanted forces on a worker.but can also be eton to move a load,the device bears the bulk of the programmed to follow a particular trajectory regardless weight by itself,while transferring to the user as a nat-of the exact direction in which the worker attempts to ural feedback a scaled-down value of the load's actual manipulate the device.For example,suppose an auto- Part weight.For example,for every 20kg of weight from an assembly worker is using an assist device to move a seat object,a worker might support only 2 kg while the de-to its final destination inside a car.The assist device can 出 vice supports the remaining 18 kg.In this fashion,the bring the seat to its final destination,moving it along worker can still sense the load's weight and judge his/her a preprogrammed path with a speed that is proportional
Exoskeletons for Human Performance Augmentation 33.2 Upper-Extremity Exoskeleton 775 ing muscle strength. In addition to electromyography (EMG) signals, the device further includes potentiometers for measuring the joint angles, force sensors for measuring the ground reaction forces and a gyroscope and accelerometer for measuring the torso angle. Each leg of HAL powers the flexion/extension motion at the hip and knee in the sagittal plane through the use of DC motors integrated with harmonic drives. The ankle includes passive degrees of freedom. Yamamoto et al. [33.10,11] have created an exoskeleton system for assisting nurses during patient handling. The lower limbs include pneumatic actuators for the flexion/extension of the hips and knees in the sagittal plane. Air pumps are mounted directly onto each actuator to provide pneumatic power. User input is determined via force sensing resistors coupled to the wearer’s skin. The measurement from force sensing resistor (FSR) and other information such as joint angles are used to determine the required input torques for various joints. Pratt et al. developed a powered knee brace for adding power at the knee to assist in squatting [33.12]. The device is powered by a linear series-elastic actuator coupling the upper and the lower portions of a knee brace. The control of this powered knee brace requires the ground reaction force measured by two load cells. The system uses a positive-feedback force controller to create an appropriate force for the actuator. Kong et al. developed a full lower-limb exoskeleton system that works with a powered walker [33.15]. The walker houses the electric actuators, the controller, and the batteries, reducing the weight of the exoskeleton system. A transmission system transmits power to the wearer’s joints from the actuators in the walker. The exoskeleton is powered at the hips and knees in sagittal plane. The input to drive the system is a set of pressure sensor that measure the force applied by the quadriceps muscle on the knee. Agrawal et al. have conducted research projects on statically balanced leg orthoses that allow for less effort during swing [33.16]. In the passive version, the device uses springs in order to cancel the gravity force associated with the device links and the person leg. Through experiments the authors showed that the device reduced the required torque by the wearer substantially. 33.2 Upper-Extremity Exoskeleton In the mid-1980s, researchers at Berkeley initiated several research projects on upper-extremity exoskeleton systems, billed as human extenders [33.17–23]. The main function of an upper-extremity exoskeleton is human power augmentation for the manipulation of heavy and bulky objects. Since upper-extremity exoskeletons are mostly used for factory floors, warehouse, and distribution centers, they are hung from overhead cranes. As can be seen in later sections, lower-extremity exoskeletons focus on supporting and carrying heavy payloads on the operator’s back (like a backpack) during long-distance locomotion. Upper-extremity exoskeletons, which are also known as assist devices or human power extenders, can simulate forces on a worker’s arms and torso. These forces differ from, and are usually much smaller than the forces needed to maneuver a load. When a worker uses an upper-extremity exoskeleton to move a load, the device bears the bulk of the weight by itself, while transferring to the user as a natural feedback a scaled-down value of the load’s actual weight. For example, for every 20 kg of weight from an object, a worker might support only 2 kg while the device supports the remaining 18 kg. In this fashion, the worker can still sense the load’s weight and judge his/her movements accordingly, but the force he/she feels is much smaller than what he/she would feel without the device. In another example, suppose the worker uses the device to maneuver a large, rigid, and bulky object, such as an exhaust pipe. The device will convey the force to the worker as if it was a light, singlepoint mass. This limits the cross-coupled and centrifugal forces that increase the difficulty of maneuvering a rigid body and can sometimes produce injurious forces on the wrist. In a third example, suppose a worker uses the device to handle a powered torque wrench. The device will decrease and filter the forces transferred from the wrench to the worker’s arm so the worker feels the low-frequency components of the wrench’s vibratory forces instead of the high-frequency components that produce fatigue [33.24]. These assist devices not only filter out unwanted forces on a worker, but can also be programmed to follow a particular trajectory regardless of the exact direction in which the worker attempts to manipulate the device. For example, suppose an autoassembly worker is using an assist device to move a seat to its final destination inside a car. The assist device can bring the seat to its final destination, moving it along a preprogrammed path with a speed that is proportional Part D 33.2
776 Part D Manipulation and Interfaces Fig.33.4 One-handed upper-extremity exoskeleton where Fig.33.3a,b Two-handed upper-extremity exoskeleton a griper allows for grasping of heavy objects [33.21] where artificially built friction forces between the load and the arms allow for grasping objects [33.25] The upper-extremity exoskeleton will significantly re- duce the incidence of back injury in the workplace, to the magnitude of the worker's force on the device.Al- which will in turn greatly decrease the annual cost of though the worker might be paying very little attention to treating back injuries. the final destination of the seat,the device can still bring Upper-extremity exoskeletons were designed based the seat to its proper place without the worker's guid-primarily on compliance control [33.26-29]schemes ance.The upper-extremity exoskeleton reflects on the that relied on the measurement of interaction force worker's arm forces that are limited and much smaller between the human and the machine.Various experi- than the forces needed to maneuver loads.With it,auto- mental systems,including a hydraulic loader designed assembly and warehouse workers can maneuver parts for loading aircrafts and an electric power extender built and boxes with greatly improved dexterity and preci- for two-handed operation,were designed to verify the sion.not to mention a marked decrease in muscle strain. theories(Fig.33.3 and Fig.33.4). 33.3 Intelligent Assist Device The intelligent assist devices (IAD)are the simplest system includes an ergonomic handle,which contains non-anthropomorphic form of the upper-extremity sys- a high-performance sensor for measuring the magnitude tems that augments human capabilities [33.30,31]. of the vertical force exerted on the handle by the operator. Figure 33.5 illustrates an intelligent assist device (IAD). A signal representing the operator force is transmitted At the top of the device,a computer-controlled elec- to a computer controller,which controls the actuator of tric actuator is attached directly to a ceiling,wall,or the IAD.Using the measurement of the operator force an overhead crane and moves a strong wire rope pre- and other calculations,the controller assigns the neces- cisely,and with a controllable speed.Attached to the sary speed to either raise or lower the wire rope to create wire rope is a sensory end-effector where the opera- enough mechanical strength to assist the operator in the tor hand.the IAD.and the load come into contact.The lifting task as required.If the operator pushes upwardly end-effector includes a load interface subsystem and an on the handle,the assist device lifts the load;and if the operator interface subsystem.The load interface sub-operator pushes downward on the handle.the assist de- Part D33.3 system is designed to interface with a variety of loads vice lowers the load.The load moves appropriately so and holding devices.Hooks,suction cups,and grippers that only a small preprogrammed proportion of the load are examples of other connections to the end-effector as force(weight plus acceleration)is supported by the oper- shown in Fig.33.6.In general,to grab complex objects, ator,and the remaining force is provided by the actuator special tooling systems should be made and connected to of the IAD.All of this happens so quickly that the op- the load interface subsystem.The operator interface sub- erator's lifting efforts and the device's lifting efforts are
776 Part D Manipulation and Interfaces a) b) Fig. 33.3a,b Two-handed upper-extremity exoskeleton where artificially built friction forces between the load and the arms allow for grasping objects [33.25] to the magnitude of the worker’s force on the device. Although the worker might be paying very little attention to the final destination of the seat, the device can still bring the seat to its proper place without the worker’s guidance. The upper-extremity exoskeleton reflects on the worker’s arm forces that are limited and much smaller than the forces needed to maneuver loads. With it, autoassembly and warehouse workers can maneuver parts and boxes with greatly improved dexterity and precision, not to mention a marked decrease in muscle strain. Fig. 33.4 One-handed upper-extremity exoskeleton where a griper allows for grasping of heavy objects [33.21] The upper-extremity exoskeleton will significantly reduce the incidence of back injury in the workplace, which will in turn greatly decrease the annual cost of treating back injuries. Upper-extremity exoskeletons were designed based primarily on compliance control [33.26–29] schemes that relied on the measurement of interaction force between the human and the machine. Various experimental systems, including a hydraulic loader designed for loading aircrafts and an electric power extender built for two-handed operation, were designed to verify the theories (Fig. 33.3 and Fig. 33.4). 33.3 Intelligent Assist Device The intelligent assist devices (IAD) are the simplest non-anthropomorphic form of the upper-extremity systems that augments human capabilities [33.30, 31]. Figure 33.5 illustrates an intelligent assist device (IAD). At the top of the device, a computer-controlled electric actuator is attached directly to a ceiling, wall, or an overhead crane and moves a strong wire rope precisely, and with a controllable speed. Attached to the wire rope is a sensory end-effector where the operator hand, the IAD, and the load come into contact. The end-effector includes a load interface subsystem and an operator interface subsystem. The load interface subsystem is designed to interface with a variety of loads and holding devices. Hooks, suction cups, and grippers are examples of other connections to the end-effector as shown in Fig. 33.6. In general, to grab complex objects, special tooling systems should be made and connected to the load interface subsystem. The operator interface subsystem includes an ergonomic handle, which contains a high-performance sensor for measuring the magnitude of the vertical force exerted on the handle by the operator. A signal representing the operator force is transmitted to a computer controller, which controls the actuator of the IAD. Using the measurement of the operator force and other calculations, the controller assigns the necessary speed to either raise or lower the wire rope to create enough mechanical strength to assist the operator in the lifting task as required. If the operator pushes upwardly on the handle, the assist device lifts the load; and if the operator pushes downward on the handle, the assist device lowers the load. The load moves appropriately so that only a small preprogrammed proportion of the load force (weight plus acceleration) is supported by the operator, and the remaining force is provided by the actuator of the IAD. All of this happens so quickly that the operator’s lifting efforts and the device’s lifting efforts are Part D 33.3
Exoskeletons for Human Performance Augmentation 33.3 Intelligent Assist Device 777 intelligent assist device,a worker can manipulate any object in the same natural way that he/she would manip- ulate a lightweight object without any assistance.There are no push buttons,keyboards,switches,or valves to 000 Controller control the motion of the intelligent assist device:the user's natural movements,in conjunction with the device computer,controls the motion of the device and its load. Figure 33.6 shows the end-effector that measures the operator forces at all times even in the presence of load- ing and unloading shock forces.This robust end-effector also includes a dead-man switch,which is installed on End-effector the handle and sends a signal to the controller via a sig- nal cable.If the dead-man switch on the end-effector is not depressed,(i.e.,if the operator is not holding onto the handle of the end-effector),the device will be sus- pended without any motion even if loads are added to or removed from the end-effector. The IAD is engineered with variety of embedded safety features.One of the most important safety charac- Fig.33.5 Intelligent assist device:the simplest form of teristics of the IAD is that the wire rope does not become upper-extremity enhancers for industrial applications.The slack if the end-effector is physically constrained from IAD can follow a worker's high-speed maneuvers very moving downward and the end-effector is pushed down- closely during manipulations without impeding the work- ward by the operator.Slack in the wire rope can have er's motion. far more serious consequences than slowing down the workers at their jobs;the slack line could wrap around synchronized perfectly and the load feels substantially the operator's neck or hand,creating serious or even lighter to the operator.With this load-sharing concept, deadly injuries.The control algorithm in the computer the operator has the sense that he or she is lifting the load,of the IAD,employing the information from various but with far less force than would ordinarily be required.sensors,ensures that the wire rope will never become For example,with a 25kg load force (gravity plus ac-slack [33.32]. celeration),the IAD supports 24kg,while the operator Another form of IAD can be seen in Fig.33.7 where supports and feels only I kg.With the assistance of the a sensory glove measures the force the wearer imposes Part D33.3 Fig.33.6a-c The end-effector(a)contains a sensor (b)that measures the force that the operator applies to the handle (c)in the vertical direction
Exoskeletons for Human Performance Augmentation 33.3 Intelligent Assist Device 777 End-effector Controller Fig. 33.5 Intelligent assist device: the simplest form of upper-extremity enhancers for industrial applications. The IAD can follow a worker’s high-speed maneuvers very closely during manipulations without impeding the worker’s motion. synchronized perfectly and the load feels substantially lighter to the operator. With this load-sharing concept, the operator has the sense that he or she is lifting the load, but with far less force than would ordinarily be required. For example, with a 25 kg load force (gravity plus acceleration), the IAD supports 24 kg, while the operator supports and feels only 1 kg. With the assistance of the a) b) c) Fig. 33.6a–c The end-effector (a) contains a sensor (b) that measures the force that the operator applies to the handle (c) in the vertical direction intelligent assist device, a worker can manipulate any object in the same natural way that he/she would manipulate a lightweight object without any assistance. There are no push buttons, keyboards, switches, or valves to control the motion of the intelligent assist device; the user’s natural movements, in conjunction with the device computer, controls the motion of the device and its load. Figure 33.6 shows the end-effector that measures the operator forces at all times even in the presence of loading and unloading shock forces. This robust end-effector also includes a dead-man switch, which is installed on the handle and sends a signal to the controller via a signal cable. If the dead-man switch on the end-effector is not depressed, (i. e., if the operator is not holding onto the handle of the end-effector), the device will be suspended without any motion even if loads are added to or removed from the end-effector. The IAD is engineered with variety of embedded safety features. One of the most important safety characteristics of the IAD is that the wire rope does not become slack if the end-effector is physically constrained from moving downward and the end-effector is pushed downward by the operator. Slack in the wire rope can have far more serious consequences than slowing down the workers at their jobs; the slack line could wrap around the operator’s neck or hand, creating serious or even deadly injuries. The control algorithm in the computer of the IAD, employing the information from various sensors, ensures that the wire rope will never become slack [33.32]. Another form of IAD can be seen in Fig. 33.7 where a sensory glove measures the force the wearer imposes Part D 33.3
778 Part D Manipulation and Interfaces Fig.33.7 An instrumented glove al- Transmitter Actuator electronics lows an operator to lift and lower objects naturally while using a hoist, similar to the way one maneuvers objects manually without activating ontroller Sensory system switches or push buttons [33.34] Fabric glove RF signal Glove Fabric glove Sensory system Stiched or glued on any part of the material handling system or the object nal is sent to the device actuator to provide the required being maneuvered [33.33,34].This instrumented glove assistance to maneuver or lift the load as a function of is always worn by the operator and therefore remains the force imposed by the operator,so that the operator with the operator.The instrumented glove generates provides only a small portion of the total force needed a set of signals as a function of the contact force be- to maneuver the device and the object being manipu- tween the glove and the object being manipulated or the lated by the device.For a person observing the operator material handling device itself.A set of signals repre- and the IAD,this interaction seems rather magical since senting the contact force is transmitted in the form of the device responds to the operator's touch regardless of radiofrequency (RF)signals to a device controller so whether the operator is pushing on the IAD or on the that a command signal is generated.The command sig- object being lifted by the device. 33.4 Control Architecture for Upper-Extremity Exoskeleton Augmentation The linear system theory is employed here to model by: the dynamic behavior of the elements of an IAD.This allows us to disclose the system properties in their v=Ge+Sfr, (33.1） simplest and most commonly used form.The more where G is the actuator transfer function relating the general approach (nonlinear and multivariable mod-input command to the actuator to the end-effector ve- els for upper-extremity assist devices)are presented locity:S is the actuator sensitivity transfer function in [33.19,20],and [33.21],where they have been ap-relating the wire rope tensile force fr to the end- plied to the devices shown in Figs.33.3 and 33.4.effector velocity,v.A positive value for v represents Part D33.4 The block diagram of Fig.33.8 shows the basic con-a downward speed for the load.Also note that,since trol technique.As discussed earlier,the force-sensing the load is connected to the end-effector,both termi- element in the end-effector delivers a signal to the nologies load velocity and end-effector velocity refer to controller,which is used to control the actuator.If e v as derived by (33.1).If a closed-loop velocity con- is the input command to the actuator,then the lin-troller is designed for the actuator such that S is small, ear velocity of the end-effector v can be represented the actuator has only a small response to the line tensile
778 Part D Manipulation and Interfaces RF signal Fabric glove Transmitter electronics Fabric glove Stiched or glued Sensory system Sensory system Glove Controller Actuator Fig. 33.7 An instrumented glove allows an operator to lift and lower objects naturally while using a hoist, similar to the way one maneuvers objects manually without activating switches or push buttons [33.34] on any part of the material handling system or the object being maneuvered [33.33, 34]. This instrumented glove is always worn by the operator and therefore remains with the operator. The instrumented glove generates a set of signals as a function of the contact force between the glove and the object being manipulated or the material handling device itself. A set of signals representing the contact force is transmitted in the form of radiofrequency (RF) signals to a device controller so that a command signal is generated. The command signal is sent to the device actuator to provide the required assistance to maneuver or lift the load as a function of the force imposed by the operator, so that the operator provides only a small portion of the total force needed to maneuver the device and the object being manipulated by the device. For a person observing the operator and the IAD, this interaction seems rather magical since the device responds to the operator’s touch regardless of whether the operator is pushing on the IAD or on the object being lifted by the device. 33.4 Control Architecture for Upper-Extremity Exoskeleton Augmentation The linear system theory is employed here to model the dynamic behavior of the elements of an IAD. This allows us to disclose the system properties in their simplest and most commonly used form. The more general approach (nonlinear and multivariable models for upper-extremity assist devices) are presented in [33.19, 20], and [33.21], where they have been applied to the devices shown in Figs. 33.3 and 33.4. The block diagram of Fig. 33.8 shows the basic control technique. As discussed earlier, the force-sensing element in the end-effector delivers a signal to the controller, which is used to control the actuator. If e is the input command to the actuator, then the linear velocity of the end-effector v can be represented by: v = Ge+ S fR , (33.1) where G is the actuator transfer function relating the input command to the actuator to the end-effector velocity; S is the actuator sensitivity transfer function relating the wire rope tensile force fR to the endeffector velocity, v. A positive value for v represents a downward speed for the load. Also note that, since the load is connected to the end-effector, both terminologies load velocity and end-effector velocity refer to v as derived by (33.1). If a closed-loop velocity controller is designed for the actuator such that S is small, the actuator has only a small response to the line tensile Part D 33.4
Exoskeletons for Human Performance Augmentation 33.4 Control Architecture for Upper-Extremity Exoskeleton Augmentation 79 force.A high-gain controller in the closed-loop veloc- ity system results in a small S and consequently a small Human change in velocity v in response to the line tensile force. (f)Operator force Also note that non-back-drivable speed reducers (usu- ally high transmission ratios)produce a small S for the Actuator system. The rope tensile force fr can be represented by: Controller fr=f+p, (33.2） where f is the operator-applied force on the end- effector;the force p imposed by the load and the end-effector is referred to herein as the load force on the line.Positive values for f and p represent down- ward forces.Note that p is the force imposed on the line and is equal to the weight and inertia force of the load and end-effector taken together: p(Load force) P=W、 w d Load (33.3) 8d山 Fig.33.8 The control block diagram of an intelligent assist device where W is the weight of the end-effector and load taken together as a whole andis the acceleration of the end-effector and load.If the load does not have any ac- If the operator pushes downward such that f=fmax, celeration or deceleration,then p is exactly equal to then the maximum downward velocity of the load is: the weight of the end-effector and load W.The oper- GK max (33.7) ator force f is measured and passed to the controller Udown 2 S(f+P) delivering the output signal e.A positive number fo in the computer is subtracted from the measurement of the If the operator does not push at all,then the maximum human force f.The role of fo is explained later.If the upward velocity of the end-effector or the load is: transfer function of the controller is represented by K, v=-GK ma +S(f+P) (33.8) then the output of the controller e is: e=K(f-fo). (33.4) Therefore,by the introduction of fo in (33.4),one need Substituting for fr and e from (33.2)and (33.4)into not be concerned about the measurement of the upward (33.1)results in the following equation for the end- human force.If S=0,the upward and downward maxi- effector velocity v: mum speeds are identical in magnitude.However,in the presence of nonzero S,for a given load and under equal v=GK(f-fo)+S(f+p). (33.5) conditions,the magnitude of the maximum upward Measuring an upward human force on the end- speed is smaller than the magnitude of the maximum effector or on the load is only possible when the line downward speed.This is very natural and intuitive for is under tension from the weight of the end-effector.If the operator.Going back to(33.5),it can be observed that the end-effector is light,then the full range of human the more force an operator imposes on the load or on the upward forces may be neglected by the sensor in the in- line,the larger the velocity of the load and end-effector strumented glove.To overcome this problem,a positive will be.Using the measurement of the operator force,the number fo is introduced into(33.4).As(33.5)shows,the controller assigns the proper pulley speed to create suffi- absence of f and p will cause the end-effector to move cient mechanical strength,in order to assist the operator upwardly.Suppose the maximum downward force im- in the lifting task.In this way,the end-effector follows posed by the operator is fmax.Then fo is preferably the human arm motions naturally.Equation (33.5)sug- set at approximately half of fmax.Substituting for fo in gests that,when the operator increases or decreases the Part (33.5),(33.6)represents the load velocity: downward force on an object,a corresponding increase or decrease occurs in the downward speed of the object. 出 u=GK(-）+sf+Pm. (33.6) Alternatively,an increase or decrease in the object's weight causes a decrease or increase,respectively,in the
Exoskeletons for Human Performance Augmentation 33.4 Control Architecture for Upper-Extremity Exoskeleton Augmentation 779 force. A high-gain controller in the closed-loop velocity system results in a small S and consequently a small change in velocity v in response to the line tensile force. Also note that non-back-drivable speed reducers (usually high transmission ratios) produce a small S for the system. The rope tensile force fR can be represented by: fR = f + p , (33.2) where f is the operator-applied force on the endeffector; the force p imposed by the load and the end-effector is referred to herein as the load force on the line. Positive values for f and p represent downward forces. Note that p is the force imposed on the line and is equal to the weight and inertia force of the load and end-effector taken together: p = W − W g d dt v , (33.3) where W is the weight of the end-effector and load taken together as a whole and d dt v is the acceleration of the end-effector and load. If the load does not have any acceleration or deceleration, then p is exactly equal to the weight of the end-effector and load W. The operator force f is measured and passed to the controller delivering the output signal e. A positive number f0 in the computer is subtracted from the measurement of the human force f . The role of f0 is explained later. If the transfer function of the controller is represented by K, then the output of the controller e is: e = K( f − f0) . (33.4) Substituting for fR and e from (33.2) and (33.4) into (33.1) results in the following equation for the endeffector velocity v: v = GK( f − f0)+ S( f + p) . (33.5) Measuring an upward human force on the endeffector or on the load is only possible when the line is under tension from the weight of the end-effector. If the end-effector is light, then the full range of human upward forces may be neglected by the sensor in the instrumented glove. To overcome this problem, a positive number f0 is introduced into (33.4). As (33.5) shows, the absence of f and p will cause the end-effector to move upwardly. Suppose the maximum downward force imposed by the operator is fmax. Then f0 is preferably set at approximately half of fmax. Substituting for f0 in (33.5), (33.6) represents the load velocity: v = GK f − fmax 2 + S( f + P) . (33.6) p (Load force) Load –W s g S G K f0 –H S W υ e Controller Actuator Human (f ) Operator force – Fig. 33.8 The control block diagram of an intelligent assist device If the operator pushes downward such that f = fmax, then the maximum downward velocity of the load is: vdown = GK fmax 2 + S( f + P) . (33.7) If the operator does not push at all, then the maximum upward velocity of the end-effector or the load is: v = −GK fmax 2 + S( f + P) . (33.8) Therefore, by the introduction of f0 in (33.4), one need not be concerned about the measurement of the upward human force. If S = 0, the upward and downward maximum speeds are identical in magnitude. However, in the presence of nonzero S, for a given load and under equal conditions, the magnitude of the maximum upward speed is smaller than the magnitude of the maximum downward speed. This is very natural and intuitive for the operator. Going back to (33.5), it can be observed that the more force an operator imposes on the load or on the line, the larger the velocity of the load and end-effector will be. Using the measurement of the operator force, the controller assigns the proper pulley speed to create suffi- cient mechanical strength, in order to assist the operator in the lifting task. In this way, the end-effector follows the human arm motions naturally. Equation (33.5) suggests that, when the operator increases or decreases the downward force on an object, a corresponding increase or decrease occurs in the downward speed of the object. Alternatively, an increase or decrease in the object’s weight causes a decrease or increase, respectively, in the Part D 33.4
780 Part D Manipulation and Interfaces upward object speed for a given operator force on the the load force is a function of load dynamics,i.e.,the object.As Fig.33.8 indicates,K may not be arbitrar- weight and inertial forces generated by the load.One ily large.Rather,the choice of K must guarantee the can find many methods to design the controller transfer closed-loop stability of the system.The human force f function K.Reference [33.19]describes the conditions is a function of the human arm impedance H,whereas for the closed-loop stability of such systems. 33.5 Applications of Intelligent Assist Device The IAD was designed with one vision in mind:min- imizing the risk of injuries associated with repeated maneuvers,and maximizing the throughput while main- taining robustness and user-friendliness.The IAD has been evaluated extensively for three applications:ware- housing and distribution centers,auto-assembly plants, and delivery services.A study on warehousing maneu- vers at distribution centers demonstrated that palletizing, depalletizing,loading and unloading trucks,and plac- ing boxes on and off of conveyor belts are the most common maneuvers.Initial studies of the distribution centers demonstrated that objects to be maneuvered in warehouses and distribution centers are mostly boxes weighing less than 27kg that require workers to maneuver them rapidly (sometimes up to 15 boxes a minute).The use of the IADs in warehouses would Fig.33.9a,b The use of IADs for mail and package deliv- have a considerable impact on reducing injuries to ery service (a)and automobile industries(b) the worker population because of the large number of warehouse workers.Figure 33.6 shows the use of ation of awkward and uncomfortable handling situations the IAD in a distribution center during a depalletizing for mail handlers: operation. the heavy weight of the sacks and letter trays and Studies of auto-assembly maneuvers revealed that letter tubs the installation of batteries,gas tanks,bumpers,instru- the lack of handles,eyelets or any other helpful ment panels,exhaust pipes,and prop shafts are important maneuvers that would benefit from IADs (Fig.33.9). operator interface on the sacks and parcels Various load interface subsystems must be employed the unpredictable shape,size,and weight of the sacks and letter trays and letter tubs at a work station for connection to various auto parts. Postal services across the world use sacks and trays Intelligent assist devices greatly reduce the risk of to hold letters,magazines,and small boxes.These sacks back injuries when used by workers performing repeti- and trays,which are manually handled by mail handlers,tive maneuvers.This reduction in injury,in turn,will are usually fully filled with magazine bundles,envelopes greatly reduce the national cost of treating back in- and parcels,and can weigh up to 32 kg.In general,at all juries.See [33.35]and [33.36]for end-effectors that distribution centers,several factors contribute to the cre- are deigned for grasping postal sacks. Part 33.6 Lower-Extremity Exoskeleton D33.6 The first field-operational lower-extremity exoskeleton a backpack-like frame on which a variety of heavy loads (commonly referred to as BLEEX)is comprised of can be mounted.This system provides its pilot (i.e., two powered anthropomorphic legs,a power unit,and the wearer)with the ability to carry significant loads
780 Part D Manipulation and Interfaces upward object speed for a given operator force on the object. As Fig. 33.8 indicates, K may not be arbitrarily large. Rather, the choice of K must guarantee the closed-loop stability of the system. The human force f is a function of the human arm impedance H, whereas the load force is a function of load dynamics, i. e., the weight and inertial forces generated by the load. One can find many methods to design the controller transfer function K. Reference [33.19] describes the conditions for the closed-loop stability of such systems. 33.5 Applications of Intelligent Assist Device The IAD was designed with one vision in mind: minimizing the risk of injuries associated with repeated maneuvers, and maximizing the throughput while maintaining robustness and user-friendliness. The IAD has been evaluated extensively for three applications: warehousing and distribution centers, auto-assembly plants, and delivery services. A study on warehousing maneuvers at distribution centers demonstrated that palletizing, depalletizing, loading and unloading trucks, and placing boxes on and off of conveyor belts are the most common maneuvers. Initial studies of the distribution centers demonstrated that objects to be maneuvered in warehouses and distribution centers are mostly boxes weighing less than 27 kg that require workers to maneuver them rapidly (sometimes up to 15 boxes a minute). The use of the IADs in warehouses would have a considerable impact on reducing injuries to the worker population because of the large number of warehouse workers. Figure 33.6 shows the use of the IAD in a distribution center during a depalletizing operation. Studies of auto-assembly maneuvers revealed that the installation of batteries, gas tanks, bumpers, instrument panels, exhaust pipes, and prop shafts are important maneuvers that would benefit from IADs (Fig. 33.9). Various load interface subsystems must be employed for connection to various auto parts. Postal services across the world use sacks and trays to hold letters, magazines, and small boxes. These sacks and trays, which are manually handled by mail handlers, are usually fully filled with magazine bundles, envelopes and parcels, and can weigh up to 32 kg. In general, at all distribution centers, several factors contribute to the crea) b) Fig. 33.9a,b The use of IADs for mail and package delivery service (a) and automobile industries (b) ation of awkward and uncomfortable handling situations for mail handlers: • the heavy weight of the sacks and letter trays and letter tubs • the lack of handles, eyelets or any other helpful operator interface on the sacks and parcels • the unpredictable shape, size, and weight of the sacks and letter trays and letter tubs at a work station Intelligent assist devices greatly reduce the risk of back injuries when used by workers performing repetitive maneuvers. This reduction in injury, in turn, will greatly reduce the national cost of treating back injuries. See [33.35] and [33.36] for end-effectors that are deigned for grasping postal sacks. 33.6 Lower-Extremity Exoskeleton The first field-operational lower-extremity exoskeleton (commonly referred to as BLEEX) is comprised of two powered anthropomorphic legs, a power unit, and a backpack-like frame on which a variety of heavy loads can be mounted. This system provides its pilot (i. e., the wearer) with the ability to carry significant loads Part D 33.6
Exoskeletons for Human Performance Augmentation 33.6 Lower-Extremity Exoskeleton 781 on his/her back with minimal effort over any type of surpass typical human limitations.BLEEX has nu- terrain.BLEEX allows the pilot to comfortably squat,merous potential applications;it can provide soldiers, bend,swing from side to side,twist,and walk on as- disaster relief workers,wildfire fighters,and other emer- cending and descending slopes,while also offering the gency personnel with the ability to carry heavy loads ability to step over and under obstructions while carry- such as food,rescue equipment,first-aid supplies,com- ing equipment and supplies.Because the pilot can carry munications gear,and weaponry,without the strain significant loads for extended periods of time without typically associated with demanding labor.Unlike un- reducing his/her agility,physical effectiveness increases realistic fantasy-type concepts fueled by movie-makers significantly with the aid of this class of lower-extremity and science-fiction writers,the lower-extremity exoskel- exoskeletons.In order to address issues of field robust-eton conceived at Berkeley is a practical,intelligent, ness and reliability,BLEEX is designed such that,in load-carrying robotic device.It is our vision that BLEEX the case of power loss (e.g.,from fuel exhaustion),the will provide a versatile and realizable transport platform exoskeleton legs can be easily removed and the re-for mission-critical equipment. mainder of the device can be carried like a standard The effectiveness of the lower-extremity exoskeleton backpack. stems from the combined benefit of the human intellect BLEEX was first unveiled in 2004,at UC Berke-provided by the pilot and the strength advantage of- ley's Human Engineering and Robotics Laboratory.In fered by the exoskeleton;in other words,the human this initial model,BLEEX offered a carrying capacity provides an intelligent control system for the exoskel- of 34kg (75Ibs),with weight in excess of that al-eton while the exoskeleton actuators provide most of lowance being supported by the pilot.BLEEX's unique the strength necessary for walking.The control algo- design offers an ergonomic,highly maneuverable,me- rithm ensures that the exoskeleton moves in concert chanically robust,lightweight,and durable outfit to with the pilot with minimal interaction force between the two.The control scheme needs no direct measure- ments from the pilot or the human-machine interface (e.g.,no force sensors between the two);instead,the controller estimates,based on measurements from the exoskeleton only,how to move so that the pilot feels very little force.This control scheme,which has never before been applied to any robotic system,is an effective method of generating locomotion when the contact loca- tion between the pilot and the exoskeleton is unknown and unpredictable (i.e.,the exoskeleton and the pilot are in contact in variety of places).This control method differs from compliance control methods [33.27,28]em- ployed for upper-extremity exoskeletons [33.17,21]and haptic systems [33.18,19]because it requires no force sensor between the wearer and the exoskeleton. The basic principle for the control of an exoskel- eton rests on the notion that the exoskeleton needs to shadow the wearer's voluntary and involuntary move- ments quickly,and without delay.This requires a high level of sensitivity in response to all forces and torques on the exoskeleton,particularly the forces imposed by Fig.33.10 Berkeley lower-extremity exoskeleton(BLEEX) the pilot.Addressing this need involves a direct conflict and pilot Ryan Steger.1:The load occupies the upper por-with control science's goal of minimizing system sen- tion of the backpack and around the power unit;2:rigid sitivity in the design of a closed-loop feedback system. connection of the BLEEX spine to the pilot's vest;3:the If fitted with a low sensitivity,the exoskeleton would Part D power unit and central computer occupies the lower portion not move in concert with its wearer.One should realize, of the backpack;4:semirigid vest connecting BLEEX to the however,that maximizing system sensitivity to external 出 pilot:5:one of the hydraulic actuators:6:rigid connection forces and torques leads to a loss of robustness in the of the BLEEX feet to the pilot's boots system
Exoskeletons for Human Performance Augmentation 33.6 Lower-Extremity Exoskeleton 781 on his/her back with minimal effort over any type of terrain. BLEEX allows the pilot to comfortably squat, bend, swing from side to side, twist, and walk on ascending and descending slopes, while also offering the ability to step over and under obstructions while carrying equipment and supplies. Because the pilot can carry significant loads for extended periods of time without reducing his/her agility, physical effectiveness increases significantly with the aid of this class of lower-extremity exoskeletons. In order to address issues of field robustness and reliability, BLEEX is designed such that, in the case of power loss (e.g., from fuel exhaustion), the exoskeleton legs can be easily removed and the remainder of the device can be carried like a standard backpack. BLEEX was first unveiled in 2004, at UC Berkeley’s Human Engineering and Robotics Laboratory. In this initial model, BLEEX offered a carrying capacity of 34 kg (75 lbs), with weight in excess of that allowance being supported by the pilot. BLEEX’s unique design offers an ergonomic, highly maneuverable, mechanically robust, lightweight, and durable outfit to 1 2 3 4 5 6 Fig. 33.10 Berkeley lower-extremity exoskeleton (BLEEX) and pilot Ryan Steger. 1: The load occupies the upper portion of the backpack and around the power unit; 2: rigid connection of the BLEEX spine to the pilot’s vest; 3: the power unit and central computer occupies the lower portion of the backpack; 4: semirigid vest connecting BLEEX to the pilot; 5: one of the hydraulic actuators; 6: rigid connection of the BLEEX feet to the pilot’s boots surpass typical human limitations. BLEEX has numerous potential applications; it can provide soldiers, disaster relief workers, wildfire fighters, and other emergency personnel with the ability to carry heavy loads such as food, rescue equipment, first-aid supplies, communications gear, and weaponry, without the strain typically associated with demanding labor. Unlike unrealistic fantasy-type concepts fueled by movie-makers and science-fiction writers, the lower-extremity exoskeleton conceived at Berkeley is a practical, intelligent, load-carrying robotic device. It is our vision that BLEEX will provide a versatile and realizable transport platform for mission-critical equipment. The effectiveness of the lower-extremity exoskeleton stems from the combined benefit of the human intellect provided by the pilot and the strength advantage offered by the exoskeleton; in other words, the human provides an intelligent control system for the exoskeleton while the exoskeleton actuators provide most of the strength necessary for walking. The control algorithm ensures that the exoskeleton moves in concert with the pilot with minimal interaction force between the two. The control scheme needs no direct measurements from the pilot or the human–machine interface (e.g., no force sensors between the two); instead, the controller estimates, based on measurements from the exoskeleton only, how to move so that the pilot feels very little force. This control scheme, which has never before been applied to any robotic system, is an effective method of generating locomotion when the contact location between the pilot and the exoskeleton is unknown and unpredictable (i. e., the exoskeleton and the pilot are in contact in variety of places). This control method differs from compliance control methods [33.27,28] employed for upper-extremity exoskeletons [33.17,21] and haptic systems [33.18, 19] because it requires no force sensor between the wearer and the exoskeleton. The basic principle for the control of an exoskeleton rests on the notion that the exoskeleton needs to shadow the wearer’s voluntary and involuntary movements quickly, and without delay. This requires a high level of sensitivity in response to all forces and torques on the exoskeleton, particularly the forces imposed by the pilot. Addressing this need involves a direct conflict with control science’s goal of minimizing system sensitivity in the design of a closed-loop feedback system. If fitted with a low sensitivity, the exoskeleton would not move in concert with its wearer. One should realize, however, that maximizing system sensitivity to external forces and torques leads to a loss of robustness in the system. Part D 33.6
782 Part D Manipulation and Interfaces Taking into account this new approach,the goal is stabilizing the exoskeleton and preventing it from falling to develop a controller for the exoskeleton with high in response to external forces depends on the pilot's sensitivity.One is faced with two realistic concerns; ability to move quickly (e.g.,step back or sideways)to the first was that an exoskeleton with high sensitivity create a stable situation for himself and the exoskeleton. to external forces and torques would respond to other For this,a very wide control bandwidth is needed so that external forces not initiated by its pilot,for example,if the exoskeleton can respond to both pilot's voluntary someone pushed against an exoskeleton that had high and involuntary movements(i.e.,reflexes). sensitivity,the exoskeleton would move just as it would The second concern is that systems with high sen- in response to forces from its pilot.Although the fact that sitivity to external forces and torques are not robust to it does not stabilize its behavior on its own in response variations and therefore the precision of the system per- to other forces may sound like a serious problem,if it formance will be proportional to the precision of the did (e.g.,using a gyro)the pilot would receive motion exoskeleton dynamic model.Various experimental sys- from the exoskeleton unexpectedly and would have to tems in Berkeley have proved the overall effectiveness of struggle with it to avoid unwanted movement.The key to the control method in shadowing the pilot's movement. 33.7 The Control Scheme of an Exoskeleton The control of the exoskeleton is motivated here through therefore considered unknown values in this analysis.In the simple one-degree-of-freedom (1-DOF)example fact,one of the primary objectives in designing BLEEX shown in Fig.33.11.This figure schematically depicts was to ensure a pilot's unrestricted interaction with the a human leg attached or interacting with a 1-DOF exo- exoskeleton.The equivalent torque on the exoskeleton skeleton leg in a swing configuration(no interaction with leg,resulting from the pilot's applied forces and torques, the ground).For simplicity,the exoskeleton leg is shown is represented by d. as a rigid link pivoting about a joint and powered by a sin- In the absence of gravity,(33.9)and the block dia- gle actuator.The exoskeleton leg in this example has an gram of Fig.33.12 represent the dynamic behavior of actuator that produces a torque about pivot point A. the exoskeleton leg regardless of any kind of internal Although the pilot is securely attached to the exo- feedback the actuator may have skeleton at the foot,other parts of the pilot leg,such as v=Gr+Sd, (33.9) the shanks and thighs.can contact the exoskeleton and impose forces and torques on the exoskeleton leg.The where G represents the transfer function from the ac- location of the contacts and the direction of the con- tuator input r to the exoskeleton angular velocity v tact forces (and sometimes contact torques)vary and are (the actuator dynamics are included in G).In the case where multiple actuators produce controlled torques on the system,r is the vector of torques imposed on the exoskeleton by the actuators.The form of G and the type of internal feedback for the actuator is immaterial for the discussion here.Also bear in mind the omission Human of the Laplace operator in all equations for the sake of leg compactness. BLEEX leg Part Fig.33.11 Simple one-DOF exoskeleton leg interacting D33.7 with the pilot leg.The exoskeleton leg has an actuator that produces a torque T about the pivot point A.The total Fig.33.12 The exoskeleton's angular velocity is shown as equivalent torque associated with all forces and torques a function of the input to the actuators and the torques from the pilot on the exoskeleton is represented by d imposed by the pilot on the exoskeleton
782 Part D Manipulation and Interfaces Taking into account this new approach, the goal is to develop a controller for the exoskeleton with high sensitivity. One is faced with two realistic concerns; the first was that an exoskeleton with high sensitivity to external forces and torques would respond to other external forces not initiated by its pilot, for example, if someone pushed against an exoskeleton that had high sensitivity, the exoskeleton would move just as it would in response to forces from its pilot. Although the fact that it does not stabilize its behavior on its own in response to other forces may sound like a serious problem, if it did (e.g., using a gyro) the pilot would receive motion from the exoskeleton unexpectedly and would have to struggle with it to avoid unwanted movement. The key to stabilizing the exoskeleton and preventing it from falling in response to external forces depends on the pilot’s ability to move quickly (e.g., step back or sideways) to create a stable situation for himself and the exoskeleton. For this, a very wide control bandwidth is needed so that the exoskeleton can respond to both pilot’s voluntary and involuntary movements (i. e., reflexes). The second concern is that systems with high sensitivity to external forces and torques are not robust to variations and therefore the precision of the system performance will be proportional to the precision of the exoskeleton dynamic model. Various experimental systems in Berkeley have proved the overall effectiveness of the control method in shadowing the pilot’s movement. 33.7 The Control Scheme of an Exoskeleton The control of the exoskeleton is motivated here through the simple one-degree-of-freedom (1-DOF) example shown in Fig. 33.11. This figure schematically depicts a human leg attached or interacting with a 1-DOF exoskeleton leg in a swing configuration (no interaction with the ground). For simplicity, the exoskeleton leg is shown as a rigid link pivoting about a joint and powered by a single actuator. The exoskeleton leg in this example has an actuator that produces a torque about pivot point A. Although the pilot is securely attached to the exoskeleton at the foot, other parts of the pilot leg, such as the shanks and thighs, can contact the exoskeleton and impose forces and torques on the exoskeleton leg. The location of the contacts and the direction of the contact forces (and sometimes contact torques) vary and are T, d A + Human leg Actuator BLEEX leg Fig. 33.11 Simple one-DOF exoskeleton leg interacting with the pilot leg. The exoskeleton leg has an actuator that produces a torque T about the pivot point A. The total equivalent torque associated with all forces and torques from the pilot on the exoskeleton is represented by d therefore considered unknown values in this analysis. In fact, one of the primary objectives in designing BLEEX was to ensure a pilot’s unrestricted interaction with the exoskeleton. The equivalent torque on the exoskeleton leg, resulting from the pilot’s applied forces and torques, is represented by d. In the absence of gravity, (33.9) and the block diagram of Fig. 33.12 represent the dynamic behavior of the exoskeleton leg regardless of any kind of internal feedback the actuator may have v = Gr + Sd , (33.9) where G represents the transfer function from the actuator input r to the exoskeleton angular velocity v (the actuator dynamics are included in G). In the case where multiple actuators produce controlled torques on the system, r is the vector of torques imposed on the exoskeleton by the actuators. The form of G and the type of internal feedback for the actuator is immaterial for the discussion here. Also bear in mind the omission of the Laplace operator in all equations for the sake of compactness. S r υ d ++ G Fig. 33.12 The exoskeleton’s angular velocity is shown as a function of the input to the actuators and the torques imposed by the pilot on the exoskeleton Part D 33.7
