NASA Robotic Positioning System

The NASA 3D welder consists of 5 axes of motion. These are, X, Y, Z, Rotary, and Theta. The Siacky welding gun is intended to be mounted to the Theta axis, the part under construction is mounted to the rotary table.   The X axis moves the gun parallel to the length of the base plate. The Y axis moves the gun transverse to the X axis. The Z axis moves the gun vertically. The Theta axis moves the gun in a 90 degree arc in the Y plane. The Rotary axis moves the part in a 360 degree rotation. All motors are servo motors.     

Each motor provides a synchro-resolver for position feedback. This is converted to position and tracked in an absolute number after the motor is powered on. The Indradrive emulates an incremental encoder output which is sent to the Siacky controller in quadrature. The resolution of this output is programmable, for the X,Y and Z axe this is 4000 count per revolution of the motor (after quadrature) The ball screw lead is 2 mm per rev. The Theta axis provides 50 counts per degree after quadrature. The rotary axis is set up to produce 4000 counts per rev (after quadrature) and which equate to 1.0 degree of rotation. Each motor has a PTC type thermal sensor. This sensor does not provide a direct reading of the temperature of the motor, rather is acts like a switch that shuts off the motor if the motor temperature exceeds 150 degrees C. The temperature display in the IndraWorks software is not correct.  

The 3D welder positioning system is connected to a control box via cables. The control box is picture below in figures 2 and 3. This control box houses the Rexroth IndraDrive servo amplifiers. All five drives are identical except for the software defining the inputs, outputs, and local servo gains. These parameters are stored on a flash RAM located on each drive. The Indradrives require 3 phase 208 volts AC at a minimum which is the design spec. The power must be within +/- 10 % of this value. The drives can operate on other higher 3 phase voltages and can also auto-detect the voltage but this should be verified in the lab before flight if higher voltages are to be used.    The power is connected to TB100, terminals 1, 2, 3. The green and yellow terminals blocks are frame ground connection points. The power cable must provide 4, 10 AWG wires. A hole with a cable strain relief is provided on the back panel for the power cable. A lockout – tagout disconnect is provided on the back panel. The handle is rotated vertically to apply power. An indicator on the front power panel labeled “Mains Power” indicates line power is present.