Emerson FM-3 Installationshandbuch PDF herunterladen (Seite 175)

161

Tuning Procedures

If the value entered is higher than the actual, system oscillation is likely. If the value entered

is lower than the actual a more sluggish response is likely but generally results in good

operation.

Response

The Response adjusts the velocity and position loop bandwidths with a range of 1 to 500 Hz.

In general, it affects how quickly the drive will respond to commands, load disturbances and

velocity corrections. The effect of Response is greatly influenced by the status of the High

Performance Gains.

With High Performance Gains disabled, the actual command bandwidth of the drive system

will be equal to the Response value. In this case the load disturbance correction bandwidth is

very low (approximately 0.1 Hz). Increasing the Response value will reduce the drive’s

response time to velocity command changes but will not affect the response to load or speed

disturbances.

When High Performance Gains are enabled, the Response bandwidth is set to the Response

value. In this case, it reflects both the velocity command and the load disturbance correction

bandwidth. Increasing the Response when the High Performance Gains are enabled will

increase loop stiffness. With High Performance gains enabled, the maximum Response level

recommended is approximately 100 Hz.

If the Inertia Ratio and Friction values are exactly correct and the High Performance Gains

are enabled, changing the Response will not affect the damping (percent of overshoot and

number of ringout cycles) to velocity command changes or load disturbance corrections but

will affect their cycle frequency. The response level generally should be decreased as the load

to motor inertia ratio increases or if High Performance Gains are enabled.

Feedforwards

Feedforward gains are essentially open loop gains that generate torque commands based on

the commanded velocity, accel/decel and the known load parameters (Inertia Ratio and

Friction). Using the feedforwards reduces velocity error during steady state and reduces

overshoot during ramping. This is because the Feedforwards do not wait for error to build up

to generate current commands.

Feedforwards should be disabled unless the absolute maximum performance is required from

the system. Using them reduces the forgiveness of the servo loop and can create instability if

the actual inertia and/or friction of the machine varies greatly during operation or if the Inertia

Ratio or Friction parameters are not correct.

The internal feedforward velocity and acceleration gains are calculated by using the Inertia

Ratio and Friction parameters. The feedforward acceleration gain is calculated from the

Inertia Ratio parameter and the feedforward velocity gain is calculated from the Friction

parameter.

When Feedforwards are enabled, the accuracy of the Inertia Ratio and Friction parameters is

very important. If the Inertia Ratio parameter is larger than the actual inertia, the result would

be a significant velocity overshoot during ramping. If the Inertia parameter is smaller than the

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Emerson FM-3 Installationshandbuch Seite 175