Interfaces torque sensors

FIGURE 35.3 The ARM Guide. The patient s arm is attached to a hand splint (S) that is attached to an orientable linear track. A dc servo motor (M) can assist in movement of the subject s arm in the reaching direction (R) along the linear track. Optical encoders record position in the reach (R), pitch (P), and yaw (Y) axes. A six-axis force sensor (F) records the forces and torques at the interface between the device and the subject. The device is statically counterbalanced with two counterbalance weights (C). 

The Design incorporates the complete SIL supervision loop according to the international SIL standards, and are defined from sensor-safety PLC-Interface relay/contac-tor-to safety braking system and driving torque disconnection (actuators). 

Frequently, an interface application will require that the PC controls the motion of an object. A device that Is often used to power or move a shaft in precise Increments, directions and speeds Is a stepper motor. Here we consider two approaches to this problem. The first uses the stepper motor, a device whose angle of rotation is known reliably from the pulses which have been sent to it. Once calibrated and Initialized, no feedback of the rotor s position is necessary, unless the speed demanded is too high or the torque required Is too great. Running a motor this way without feedback is called OPEN LOOP. The second method uses feedback, is a CLOSED LOOP approach, and Is called a servo system. The servo system can respond more quickly and accurately than the open-loop stepper motor system and Is relatively insensitive to hardware variations. However, It requires position sensors as well as more complicated drive electronics to ensure stability. 

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