Hypertherm Phoenix 8.0 - Manual (Page 445)

Motion Overview
438
Typical Velocity and Position Loop System
The motion command starts as digital output within the control and is converted to a +/-
10 Vdc analog output for use by the motors. This conversion of the motion command
within the control is referred to as the digital to analog converter (DAC) output and is
performed by the motion control card. After the analog output leaves the control, it
travels to a drive amplifier that increases the voltage output to the motor and creates
motion. Also, there is usually a linear relationship between the voltage sent and the
machine speed. For example, if 10 volts is the maximum machine speed, 5 volts is half
maximum machine speed. Additionally, the polarity of the output (DAC polarity +/-) to
the amplifier dictates the direction of the motor rotation. In most applications and in the
following application description, the feedback device is an encoder.
Encoders
An encoder is a feedback device that provides
signal pulses as the motor turns. The diagram at
the right illustrates the basic concept of an encoder.
Although this does not represent all encoder
feedback device technology, this illustration
provides a visual aid to help understand the
process.
The illustration shows a disk with small holes cut
out along the outer edge. The light source projects
a beam of light downward through the holes in the
disk. As the disk turns on the end of the motor
shaft, the light passes through the disk and creates pulses. The receiver below the disk
picks up the light pulses and sends that feedback to the control.