RoboteQ Dual Channel Digital Motor Controller AX500 Manual do Utilizador descarregar pdf (Página 70)

Closed Loop Position Mode

70 AX500 Motor Controller User’s Manual Version 1.9b. June 1, 2007

required for each motor. Additional switches may be added as needed for the second

motor and/or for a manual Emergency Stop. Since very low current flows through the

switches, these can be small, low cost switches.

The principal restriction of this technique is that it depends on the controller to be fully

functioning, and that once a switch is activated, the controller will remain inactive until the

switch is released. In most situations, this will require manual intervention. Another limita-

tion is that both channels will be disabled even if only one channel caused the fault.

Important Warning

Limit switches must be used when operating the controller in Position Mode. This

will significantly reduce the risk of mechanical damage and/or injury in case of dam-

age to the position sensor or sensor wiring.

Using Current Limiting as Protection

It is a good idea to set the controller’s current limit to a low value in order to avoid high cur-

rent draws and consequential damage in case the motor does not stop where expected.

Use a value that is no more than 2 times the motor’s draw under normal load conditions.

Control Loop Description

The AX500 performs the Position mode using a full featured Proportional, Integral and Dif-

ferential (PID) algorithm. This technique has a long history of usage in control systems and

works on performing adjustments to the Power Output based on the difference measured

between the desired position (set by the user) and the actual position (captured by the

position sensor).

Figure 42 shows a representation of the PID algorithm. Every 16 milliseconds, the control-

ler measures the actual motor position and substracts it from the desired position to com-

pute the position error.

Motor

SW1

SW2

Manual

Emergency

Stop Switch

Emergency Stop InputGround

Controller

FIGURE 41. Safety limit using AX500’s Emergency Stop input

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RoboteQ Dual Channel Digital Motor Controller AX500 Manual do Utilizador Página 70