described in the position and velocity sensing sections. The seventh A/D converter was

connected to a type "T" thermocouple panel meter for monitoring the temperature of the

hydraulic fluid during operation. All of the A/D converters represented an input voltage

ranging from -5 volts to +5 volts with a value ranging from 0 to 4095. The A/D converters were

plugged directly to the VME bus of the control computer.

 Parallel I/O signals. Control of components which required a signal depicting either on

or off operation was accomplished by the addition of a parallel card and an Opto-22 switching

panel. The parallel port of the card was connected to the Opto-22 panel. The Opto-22 panel

allowed the addition of either input or output modules. The output modules acted as electronic

relays for switching other components based on the signal from the corresponding pin of the

parallel port. Output modules were used to switch 120 VAC for the picking mechanism lights,

the solenoids of the picking mechanism actuator, and the main hydraulic dump valve. Input

modules were added to the card to sense the status of the hydraulic dump valve and the servo

amplifiers. A 5 VDC input module was used to sense the position of push button safety switches

which were located at various strategic locations in the lab and connected in series to one

another. Signals from the input modules were routed to the appropriate pins of the parallel

card.

 Servo mechanisms. Joint motion of the manipulator was accomplished by two

hydraulic rotary actuators and a hydraulic motor. Hydraulic fluid flow to these actuators was

controlled by servo valves. The rate of fluid flow through a servo valve was proportional to

the amount of current passing through the coil of the valve. Three Vickers EM-D-20 servo

amplifier modules were used to adapt the output voltage from the control computer to a coil

current usable by the servo valves. The output voltages from the computer were generated by

three 12-bit digital-to-analog (D/A) converters. Gains for the servo amplifiers were adjusted

to produce the maximum coil current to each of the valves at the maximum output voltage of 

2.5 volts from the D/A converters as listed in Table 4.1. The bandwidth characteristics for the

servo amplifiers and servo valves are also presented in Table 4.1.