MaxAcc

General

Functional Description

The parameter represents the maximum acceleration on the drive shaft (gear box outside) in [units / seconds^2].

Theoretically, this acceleration can be reached with 96 % of the peak torque if the moment of inertia J_Load and J_Gear is set correctly. In practice, there are deviations from this theoretical value that can be caused by

• deviations in the measurement,

• deviations in the torque constant or force constant or

• deviations in the moment of inertia or the mass.

The remaining 4 % are a control-loop reserve. This control-loop reserve is intended for

• overshoots of the control-loop,

• friction moments or friction forces and

• other external moments or forces.

At high frictional torque, the control-loop reserve is not enough and the maximum acceleration cannot be reached. MaxAcc is adjusted automatically to changes of J_Load and J_Gear as long as it is not limited by UserMaxAcc also. The parameters ViscousFriction and StaticFriction have no effect on MaxAcc. Changes on J_Load and J_Gear are taken over directly; changes on UserMaxAcc are only taken over by a Sercos phase-start.

If by real axes UserMaxAcc is unequal zero, then the value for MaxAcc is only taken over by a Sercos phase up if it is smaller than the value calculated by the system.

If by virtual axes UserMaxAcc is unequal zero, then this value is written (by the Sercos phase up) in MaxAcc. Therefore, the value of UserMaxAcc is also taken over if it is greater than the default value (by UserMaxAcc = 0).

The parameter is used by function blocks for generating the reference values in which an acceleration limitation is realized or where the acceleration for the references value profile can be parameterized. Limitations of the parameters ControllerStopDec and ControllerStopJerk depend on MaxAcc.

Special Features by Asynchronous Motors

With asynchronous motors, MaxAcc is calculated from data which may not be exact figures, only estimated. This may lead to the potential of the indicated value of MaxAcc being not equal to the real value that can be indicated in the drive.

The following graphic shows the dependency with other object parameters for rotary drives:

The following graphic shows the dependency with other object parameters for linear drives:

Example:

Entering J_Load has a direct impact on the parameter MaxAcc. A revision of MaxAcc only has an impact on ControllerStopDec if,

• a Sercos phase up takes place or

• the parameter ControllerStopDec is modified.