Axis Control Module

The axis control module provides the circuits to integrate multiple axis so that the robot can move more than one axis at the same time. The axis control module is important because the velocity and torque commands of each axis amplifier and motor must be carefully controlled when the robot moves multiple axes at the same time. ill. 1 shows a diagram of the axis control module with six amplifiers connected to it. A motor is connected to each amplifier and the feedback sensors for position and velocity may be connected to the amplifier or they may be connected directly to the axis control module depending on the manufacturer of the robot. The axis control module is connected to the back plane with the main CPU.

Above: ill. 1: Axis control module with six motor amplifiers connected.

When the robot is executing a program, the coordinates of each new robot position is sent to the axis control module. The axis control module will calculate the number of pulses each motor should move and the velocity at which each motor should operate to provide smooth motion at the end of the robot arm. For instance, if the base of the robot is to rotate 10°, the waist is to move 3 in., the upper arm is to move 12 in., and the wrist is to rotate 120°, all of the motors can't run at the same speed or the result at the end effector is that one part of the move will be completed before the other moves are completed, which would result in jerky motion. The axis control module synchronizes all of the axes so the movement at the end of the robot arm is smooth.

It's also important to understand that some axes must move to accommodate the motion of other axes. For instance, when the upper arm is to move up or down 2 in. and the wrist is to keep the same orientation, the wrist pitch and yaw motors must also be moved slightly to keep the wrist at the same orientation. The axis control module has a math coprocessor that uses complicated formulas (algorithms) to compute all of the motions and velocities that are involved in every move.