Scanning

Requirements

In order to use PC-DMIS to scan your parts with an analog probe (SP600 or SP25), there are several requirements that need to be met.

• SMP400 controller

• Sheffield Interfac.DLL version 2.68 or higher

• PC-DMIS Version 3.7 MR2

• Calibrated CMM

Functionality

The chart below summarizes the available PC-DMIS scanning features and the status of their support on Sheffield CMM’s with the SMP400.

Unsupported scan controls/methods

• Boundary Types (Plane, Cylinder, Cone): Boundary conditions tell PC-DMIS when to stop a scan. Only the spherical boundary type is functional with the SMP400. Use of the other types may cause continuous and erroneous scans.

• Control Points: Control Points are not supported, so variable scan speeds during a scan cannot be done. Scans performed at their initial speed end at that same speed.

• Defined Scans: The Generate button which allows you to define a scanning path to be overlaid upon the CAD is not supported as it generates Defined type scans which the controller does not support.

Scanning Limitations

• There is a 4000-point limitation in the Sheffield controller. Scans requiring more data must partially scan features and combine them to create the desired feature. No warning is issued when the buffer is full and the CMM continues the scan path even after the buffer has been filled.

• ScanSpeed does not affect the Center scan, it is at a fixed speed determined by the controller.

• Defined Scans (where the actual nominal scan points are sent to the controller) are not supported.

OPEN/CLOSED LOOP Scanning

• Currently, OPEN LOOP only works with circular path/features such as CIRCLE and CYLINDER. This is not referring to LINEAROPEN and LINEARCLOSED scans.

• Feature Scans (e.g. Circle, Cylinder, and Axis) are implemented as Open Loop scans. Other scans (Linear Open, Linear Closed, Center, Rotary) are implemented as Closed Loop. So, the final implementation will be that the Feature Scans are Open Loop, and the others are Closed Loop. The registry entry currently used is removed.

• Controls over whether the scans being executed will either be OPEN or CLOSED are accomplished by editing the Settings Editor value: UseClosedLoop under the Sheffield tab.

If you wish to control the type of scan being performed for a measurement routine, you must quit PC-DMIS and launch the Settings Editor.

OPEN LOOP UseClosedLoop FALSE

CLOSED LOOP UseClosedLoop TRUE

There are no controls to change to OPEN or CLOSED by PC-DMIS commands, or by the loss of surface with an OPEN loop. The global value set in by the Settings Editor program is a global default.

Scan Speeds

• In order to scan in OPEN LOOP at speeds greater than 35mm/s, the user should define a repeatable alignment using more than the minimum number of points. If the scan begins and deflects at a value other than expected there isn’t any method to reduce speed automatically and scan in CLOSED LOOP.

• CLOSED LOOP scans should not be executed faster than 20mm/s on diameters 50mm or smaller. This is application specific but if the user experiences visible CMM vibrations and poor measurement results while scanning they may be scanning the feature too fast for CLOSED LOOP.

• To best apply all analog scanning applications, it is recommended the user begin measuring the feature at the slowest speed they can and as they monitor performance and accuracy, the user can increase the speed until they reach a point where they accept measurement results before degraded accuracy in relation to speed.

Recommended Settings

Settings Editor

Parameter Settings - Opt. Probe tab