How To Build A Probe File
The first step in CMM programming is to define which probes you will be using during the inspection process.
PC-DMIS supports a wide variety of probe types and calibration tools. A new part program must have a probe file created or selected before any measurements can be taken. To access the probe options select “Insert” from the menu bar and then select “Hardware definition” and then probe from the drop down menu.
This will bring up the probe utilities dialog box which displays the probe data for the active tip, this allows you to create new probe files as needed. Probes can also be calibrated using this option.
Probe File Name – The Directory List displays the current probe file TIP2BY20.
Create a new file name
Simply highlight the current name and type in a new one. If a probe file has already been saved under the keyed in name, PC-DMIS will load the previously saved file into the current part program.
Probe Description area – The Probe Description Edit area allows you to define the probe, extensions and tip(s) that will be used in the part program. The Probe Description drop down window displays the available probe options in alphabetical order. The bottom right hand window will display a graphical representation of the probe as it is being assembled.
Measure – Clicking on Measure will take you into the calibration environment where the currently selected tip(s) will be calibrated on a known standard (typically a sphere).
Tolerances – This option allows the user to supply the tolerance value used in the Collision Detection option.
Add Angles – The Add Angles option allows you to create a list of AB positions when using an indexing head such as the PH9 and PH 10. Once a position has been calibrated it can be recalled at any time during the part program.
Results – This option will display the results of the most recent probe calibration. In addition to displaying the probes diameter and thickness, it will also provide the actual angle and roundness of the sphere. These measured results allow you to verify the accuracy of the calibration.
Mark Used – This option will automatically search the current part program for AB angles. PC-DMIS then adds any AB angle combinations that are found to the current probe configuration.
Global Used – The Global Used button searches for tips used in other part programs by the currently active probe file. It then adds them to the Active Tip list and marks them for calibration.
Creating a new Probe File
OK – When any functions that were required have been completed click on OK to close the Probe Utility dialog box and update the probe file.
Cancel – This command button will discard any changes to the probe data file. Select Yes to end the operation without making any modifications. Selecting No will return you to the current probe file.
Probe Utilities – Step 1
Highlight the name currently in the Probe File, either hit backspace or Delete and enter the new Probe File name. Note that if the file does not exist, all entries are deleted from the previous probe file.
Probe Utilities – Step 2
Click on the down arrow to display the probe heads which are available.
Scroll down the list until you come to the required
e.g.; Global_AA_adapter. Click on it in the list and it will begin the probe configuration.
The graphic window is updated to show the configuration so far.
Note the line “Empty Connection #1”, PC-DMIS has built in intelligence which lets it know that this probe selection alone is not enough to complete the configuration.
Click on the Empty Connection #1 line so that it is highlighted (this then becomes the insertion point for what we are about to do) and then click on the down arrow in the Probe Description window.
This time the list contains only those components that will fit into a basic PH1OM head.
As we wish to connect a TP20 probe to this head which has an 8mm thread, we must first select the “CONVERT30MM_TO_M8THRD” connector from the list. (Connector not required on the PH1OT, all depends on the probe head being used on the CMM)
Click on the required head and it will be added to our configuration and the graphics window updated. PC-DMIS knows that we have an open connection and displays the line “Empty connection #1”
Probe Utilities – Step 4
Click on the “Empty Connection #1” so that it is highlighted and then click on the probe Description down arrow. The list this time only contains those items with an 8mm thread that will fit into this connector. Scroll down the list until you get to the “PROBE_TP20” probe and then click on it to add it to our configuration.
All that now remains is to add the final piece to our probe assembly which is a stylus. Click on the “Empty Connection #1” line and then the Probe description down arrow. The TP20 probe has a 2mm thread in the end of it and so only those styli which have a 2mm thread are listed. Scroll down the list until you get to the 2mm by 20mm stylus (2mm ball by 20mm long), click on it to add it to our configuration. This time when the stylus is added, there is no longer an empty connection, as this is a valid completed configuration, this can be seen by viewing the graphic. This completes the configuration of the probe, if we were not going to calibrate the probe at this time we could click on the OK button to close the dialog box and save the probe file.
Calibrating the probe
Now that the probe has been defined, it needs to be calibrated. Calibrating a probe not only lets PC-DMIS know where the probe is relative to the machine, but it also accurately measures the effective tip diameter. Once again select Probe from the “INSERT” menu and the appropriate Probe File name, in this instance “2BY20”.
Probe Utilities – Select Measure
Select Measure in the Probe Utilities dialog box.
Before we can actually measure the probe we have to define which tool we are going to use to calibrate the stylus or tip. If we had previously defined a tool it could simply be selected from the List of Available Tools.
The first time around however we need to add a tool to the list, this is accomplished by clicking on the Add Tool button. The Add Tool function tells PC-DMIS what type of tool is being used to calibrate the stylus and its orientation to the CMM.
Probe Utilities – Add Tool Dialog
When the Add Tool dialog box appears, enter a name for the tool. Make sure that you pick a name that you will recognize if you were selecting it from the List of Available Tools. In this example we have entered the name “Calibration Sphere”.
There are various tool types available for calibration purposes, the most popular for spherical probes being a sphere. If sphere is not displayed as the Tool Type select it from the list.
Next enter the vector of the tool. The vector direction required is the vector running through the centre of the shank of the tool and out through the sphere. If using a single sphere this is typically 0,0,1.
Enter the diameter of the sphere. The accuracy to which you input this value will affect the accuracy of the calculated tip size. Select OK to accept this information
Make sure that the tool that you wish to use for the calibration is selected in the List of Available Tools.
Enter the number of hits that you wish to take (minimum 4 hits), the system defaults to 5 hits for a sphere.
Enter the Pre hit distance (the distance from the theoretical hit location that the CMM will travel at normal move speed before changing to touch speed) – or accept the default.
Enter the Move Speed or accept the default. Enter the Touch Speed or accept the default.
Recommended; Use the same Touch speed as in the part programme.
Select Manual or DCC for the calibration.
When all selections have been made click on the Measure button.
Probe Utilities – Qualification Tool Moved
PC-DMIS will display a message asking if the position of the tool has been changed since the last time a calibration was done. If this is the first calibration or the reference tip and/or you have moved the tool since the last calibration click on the Yes button. This also applies if the machine has been switched off. This question is important especially if you selected DCC as the method of calibration. If PC-DMIS is told that the position has not changed, it will use the previous coordinates of the sphere as the target to move to.
Depending on the selection between Manual and DCC, PC-DMIS will either prompt the operator to take the required number of hits manually around the sphere or will automatically take them The tip is then qualified.
If you are qualifying a tip under DCC mode and the tool has been moved, then
PC-DMIS will only ask for one manual point normal to the probe (e.g. on the top of the sphere for a vertical probe).
After this single point PC-DMIS will take a further 3 points to establish an approximate centre of the sphere, a further 5 points will then be taken (or the number of points defined in the Measure Probe dialog box) at the optimum spacing to calculate the tool centre.