Glossary

Clockwise

Rotating in the direction of increasing encoder or transducer counts.

Closed Loop Mode

Sometimes called Servo mode. In this mode the difference between the Target and Actual position/pressure is the error that the PID routine uses to compute a corrective drive that minimizes the error.

Counter-Clockwise

Rotating in the direction of decreasing encoder or transducer counts.

Extending

Going in the direction of increasing encoder or transducer counts.

GSD file

This is a device description file required by every PROFIBUS device. The RMC’s GSD file is installed with RMCWin’s program files. Refer to PROFIBUS Configuration for details on using this file.

Hard Stop

An emergency stop condition where the drive is immediately set to the null drive value.

LDT

Linear Displacement Transducer. Technically, this is any sensor that can sense a linear position. Many use this term interchangeably with MDT.

MDT

Magnetostrictive Displacement Transducer. A device that senses position by sending an electron pulse down a wave guide. A twist is imparted on the wave guide as the pulse reaches the magnetic field of a magnet. The twist takes time to be sensed at the transducer head. It is this time is proportional to the distance between the transducer head and the magnet. The RMC measures this time to determine the distance.

Note: Balluff and Temposonics rods are both MDTs whereas any linear measurement device can be a LDT.

Open Loop Mode

The drive output is set to a value without any corrective action taken by the PID routine.

PID

Proportional Integral Derivative. A simple algorithm used by the motion controller to reduce the error between the target and actual position, pressure, etc. The three words of this acronym represent the three types of gains used for controlling a system. See PID Loop below.

PID Loop

The process of repeatedly executing the PID routine

Error: = Target - Actual

E0: Current Error, Error for current Target and Actual

E1: Previous Error, Error for previous Target and Actual

U0: Current output

U1: Previous output

Kp: Proportional Gain

Ki: Integral Gain

Kd: Differential Gain

Proportional Term: U0p = Kp * E0

Integral Term: U0i = U1i + Ki * E0

Differential Term: U0d = ( E0 - E1 ) * Kd

The Sum is: U0 = U0p + U0i + U0d

The PID LOOP is:

DO FOREVER

WAIT FOR NEXT TIME PERIOD

READ ACTUAL FROM POSITION OR PRESSURE SENSOR

E0 = TARGET - ACTUAL

U0p = Kp * E0

U0i = U1i + Ki * E0

U0d = ( E0 - E1 ) * Kd

U0 = U0p + U0i + U0d

E1 = E0

CALCULATE NEXT TARGET POSITION

END

Retracting

Going in the direction of decreasing encoder or transducer counts.

Soft Stop

An emergency stop condition where the drive ramps down to the null drive value.

SSI

Synchronous Serial Interface. A widely accepted controller interface to sensors and absolute encoders. Position data is encoded in a 13- to 25-bit binary or Gray Code format and transmitted over a high-speed synchronous interface.

Target Generator

The part of the motion control software that determines where the axis should be at any moment using the requested position, speed, acceleration and deceleration provided by the user. A different target generator is used for position control, speed control, gearing, synchronized moves and pressure control.