Delta RMC151 User Manual download pdf (Page 111)

3 Controller Features

damping must be provided initially with the Differential gain. This is the primary

difference between the tuning methods of velocity drives and torque drives.

• Feed Forwards

On a velocity mode system, the Velocity Feed Forwards often provide most of the

drive required to move the axis and may therefore be large. On a torque mode

system, the Velocity Feed Forwards are basically only for overcoming friction and are

often small. On torque mode systems, the Accel Feed Forwards do a lot of the work.

Effect on Commands

The Open Loop Absolute (11) and Open Loop Relative (12) commands are intended only

for velocity drives. The Open Loop Rate (10) command can be used on either, but the

Control Output voltage should be kept very low for torque mode systems to keep them

from running away.

3.5.12. Advanced

3.5.12.1. Position I-PD

Position I-PD is an algorithm that can be used to perform closed-loop motion control on a

position axis. I-PD stands for the central gains used in this mode: Integral, Proportional, and

Differential. The "-" indicates how the algorithm uses these gains.

For most motion applications, the Position I-PD is not as well-suited as the Position PID

However, the Position I-PD differs from the Position PID in that it can easily be tuned so that it

does not overshoot. The Position I-PD is therefore very suitable for applications where the

Target Position jumps. An example is an axis geared to a reference input that makes discrete

jumps. The Position I-PD typically does not respond as quickly and does not use Feed

Forwards. Therefore, it will always lag behind the Target Position when moving.

Position I-PD Advantages

• Easy to tune for minimal overshoot, making it excellent for controlling an axis that

follows an irregular target, such as step jumps or a joystick.

• Is not disrupted by a saturated Control Output.

Position I-PD Disadvantages

• Not well suited for following a specific target profile.

• Does not track position changes very quickly. May take longer to get into position.

Motion Commands in Position I-PD Mode

The following commands are designed for use only with Position I-PD and automatically

put the axis into the Position I-PD control mode during the commanded motion:

• Move Absolute (I-PD) (28)

This command immediately sets the target to the requested position. It does step-

jump; it does not ramp it.

• Move Relative (I-PD) (29)

This command immediately sets the target to the requested distance from the

specified position (Target, Actual, or Command). It does step-jump; it does not ramp

it.

To use the Position I-PD control mode with other motion commands, first use the

Set

Pos/Vel Ctrl Mode (68) command to set the Next Pos/Vel Control Mode to Pos I-PD. The

next closed-loop motion command will use the control mode specified in the Next Pos/Vel

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Delta RMC151 User Manual Page 111

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