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