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Motion Control Limits

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kjwoodsISIS edited this page Apr 21, 2016 · 3 revisions

Setting Soft Limits

Note: In the examples below, the LARMOR sample stack is used as an illustration. Other instrument devices (e.g. monitors, polarisers, analysers) follow similar principles. Green ellipses in the screenshots are used to highlight certain buttons.

To limit a range of motion for a particular axis, follow the steps outlined below:

  1. Click on the sample stack in the synoptic display to bring up the Sample Stack OPI showing the individual axes of the sample stack.
  2. Click on the "View Motors" button to display an OPI showing all the motors that drive the axes.
  3. Each motor panel has a "More Details..." button. Click on the "More Details..." button to drill down to the configuration page for each motor.
  4. On the motor configuration OPI, enter the desired maximum limit in the "Hi Limit" box in the "User" column, and the minimum limit in the corresponding "Lo Limit" box.

The MAXIMUM limit is used for restricting motion in the POSITIVE direction towards the UPPER limit switch, i.e. INCREASING encoder counts and, conversely, the MINIMUM limit is used for restricting motion in the NEGATIVE direction towards the LOWER limit switch, i.e. DECREASING encoder counts.

If for any reason the current position ends up being outside this newly defined range, e.g. if the setpoint entered was one of the limits and the motion ran on slightly, then the system will not allow the axis to return to within the range. This anomaly is currently being investigated and the workaround to use in the meantime is to:

  1. Temporarily redefine the appropriate nearest softlimit so that the new range includes the axis's current position (axis is now "In Range")
  2. Move the axis back to within the original range
  3. Redefine the softlimts for the original range.

N.B. The direction of rotation of the motor(s) may not relate to the direction of the motion stage in question. E.g. in the case of a jaws set, a single jaw may move in a negative direction whereas the motor itself may move in a positive one. This is because Cartesian coordinates are used for the whole system and its individual axes usually have their maximum limits set furthest from the centre of the jaws set. i.e. at the lowest level, all the jaws move in a positive direction away from the centre.

These instructions are also present in the following file: C:\Instrument\Docs\motion_control\Setting_Soft_Limits.pdf

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