Performing a Low Level Matrix Calibration

You should redo the low level matrix calibration at these times:

• Whenever you remove and remount the probe head or wrist

• Whenever the probe sustains damage or has been replaced

• During periodic intervals based on your specific needs

Prerequisites

Before following the calibration procedure below, ensure that you meet these prerequisites:

• You must run PC-DMIS in Online mode.

• You must run PC-DMIS using a CMM that has a lower matrix.

• You must have an analog probe that utilizes a lower matrix. Some of these include the SP600, SP80, LSP-X1, LSP-X3, LSP-X5, and so on.

• You should use a rigid stylus that deflects as little as possible during the procedure.

Calibration Procedure

1. Access the Probe Utilities dialog box (Insert | Hardware Definition | Probe).

2. Ensure that the angles that you need exist in the Active tip list.

3. From the Active tip list, select the angle used as the reference position. In most instances, this should be the angle used for the Z- direction. Unless you have a horizontal arm, this angle is usually the T1A0B0 tip.

4. Click the Measure button to open the Measure Probe dialog box.

5. Select the Lower matrix option button from the Type of Operation area. This option appears only when you work in Online mode with a machine type that supports a lower matrix, and a probe type that requires a lower matrix.

6. If desired, change the values in the Prehit / Retract, Move Speed, or Touch Speed boxes.

7. Select an appropriate tool from the List of Available Tools list.

8. Click the Measure button. PC-DMIS gives a warning message that tells you that if you continue, you will change the machine specific parameters for the lower level matrix on the controller itself. Click Yes to continue the calibration.

9. PC-DMIS displays another message asking if the qualification tool has moved. Click Yes or No.

10. PC-DMIS next displays a message asking you to take one hit normal to the calibration tool. If you're working from the Z- position, take the hit on the very top of the tool. After taking this one hit, PC-DMIS takes over and finishes determining the center location of the calibration tool. It does this by taking:

• 3 hits around the sphere

• 25 other hits around the sphere

11. Once PC-DMIS finds the center location of the tool, the actual low level matrix calibration begins. In most applications, PC-DMIS will take 22 hits (11 hits in one direction and 11 hits in another direction forming a cross pattern) on the X+, X-, Y+, Y-, and Z+ poles of the calibration sphere, for a total of 110 hits. This typically takes five to ten minutes to complete.

12. PC-DMIS then presents you with nine numbers along with a message asking if these numbers are correct. These are the lower level matrix values. If you started the calibration with the probe in the Z- direction, then the ZZ value (value in the third row and third column) should be between about 0.14 and 0.16. All other values should be less than or about 0.1.

13. If the values are correct, click OK. PC-DMIS will then overwrite the lower level matrix values on the controller with the newer values. When complete, PC-DMIS prompts you to confirm it’s OK to proceed. On some machine types, PC-DMIS may have to send an emergency stop command to the machine to update the values. If so, wait for the prompt and then restart the machine before you click OK.

14. Click OK in the message box.

PC-DMIS once again displays the Probe Utilities dialog box. Notice that the reference tip in the Active tip list isn't calibrated. The lower level calibration doesn’t calibrate the actual tip angles. Tip angles get calibrated when you perform the upper level matrix calibration procedure.

If you don't have a good low level matrix, you will experience problems in some scanning routines, and the machine may not be able to complete some scans. In addition, you will experience inaccuracies.