MC-LookAhead OB

Description

When you create a kinematics technology object as of V5.0 for S7-1500T Motion Control, the organization block MC‑LookAhead [OB97] is created automatically.

The movement preparation of the kinematics technology object is calculated in the MC‑LookAhead [OB97] organization block.

The MC‑LookAhead [OB97] is write-protected. The contents cannot be changed.

All jobs of the job sequence are prepared in advance within the MC‑LookAhead [OB97]. In this way, less time is required for movement preparation in the MC‑Interpolator [OB92] organization block and you can set a shorter application cycle of the MC‑Servo [OB91] organization block.

Block call and priority

The MC‑LookAhead [OB97] is not called cyclically according to the configured priority in the execution system of the CPU.

You configure the priority of the MC‑LookAhead [OB97] in the properties of the organization block under "General > Attributes > Priority". You can set values from 14 to 16 (default setting 15) for the priority. The priority of MC‑LookAhead [OB97] must be lower than the priority of MC‑Interpolator [OB92].

Cycle load

You can configure the maximum cycle load for the MC‑LookAhead [OB97].

You configure the maximum cycle load of the MC‑LookAhead [OB97] in the properties of the organization block under "General > Cycle load > Maximum cycle load". You can set values from 1% to 40% (default setting 20%) for the maximum cycle load.

Select the cycle load of the MC‑LookAhead [OB97] in such a way that the CPU can process all technology objects for Motion Control in one application cycle.

Process response

If the application cycle is not observed, overflows occur. Note the following response to overflows:

The CPU tolerates a maximum of three consecutive overflows of MC‑Interpolator [OB92].

The execution of an MC‑Interpolator [OB92] may only be interrupted by an MC‑Servo [OB91] call.

If more overflows or interruptions occur, the CPU switches to STOP mode.

You can find more information on the process response in the section "Operational Sequence and Timeouts".