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 loads780 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 arbitrar￾ily 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: 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 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, instru￾ment 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 cre￾a) b) Fig. 33.9a,b The use of IADs for mail and package deliv￾ery 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 repeti￾tive maneuvers. This reduction in injury, in turn, will greatly reduce the national cost of treating back in￾juries. 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