Dial Gauge Testing in no time at all

Dial gauges and high definition display measuring devices, colloquially often also known as a dial gauge, are precision ­instruments. As with all mechanical devices, they are also subjected to wear and tear, aging, or are adversely affected by ­“accidents,” such as hard impacts. It is therefore necessary to test them for their measurement accuracy on regular intervals. This is also stipulated in various standards, as well as the required documentation for this.
With a larger stock of measuring ­instruments this is an effort and cost ­factor not to be underestimated. In order to remedy this situation, Feinmess Suhl GmbH has developed the new, fully automated testing device MFP-100.01 BV. Small drive specialist FAULHABER ensures the necessary highly precise mechanical movement process

Measurement and Documentation

The principle of the dial gauge is based on a plug gauge, which is pushed into a housing against a spring force. This moves an indicator, displaying the ­measurement value on a scale, proportionally to the path via a gear. The display value may not exceed a certain error, compared with a norm, and must remain approximately ­equally low across the entire measurement ­range. Therefore, the ­clock is normally mounted in a ­temperate environment for testing purposes and mechanically/­optically measured by hand. The tester then records the respective target and actual values, and issues a test badge. This ­procedure can now be drastically simplified thanks to modern electronics. After the test item has been inserted, the dial gage and high definition display testing device will ­assume all further work steps.
A camera with adjusted lighting records a non-glare image of the gage display. The connected computer analyses this image, and internally determines the zero point, as well as the scale graduations for the test. Now, it actuates an EC servo motor, which supplies the highly precise mechanical adjustment necessary for the measuring sleeve of the testing device. In this way, the entire ­measurement range can be run through step-by-step in the previously determined steps. The dial gauge display associated with the target ­specification at the measuring sleeve and is recorded, analyzed, and stored parallel to the measuring process in a database. The complete, individual documentation of the test item is therefore accessible on the screen at any time. If the ­measurement result is within the scope of the specification, the testing device also issues the necessary test badge at this time. The entire test run requires only a fraction of the currently usual time. In this manner, even larger stocks of measuring devices can be tested in a short amount of time, and documented consistently.

Sensitive Drive

In order to be able to completely replace the ­precision test pieces of the ­conventional testing method with an auto­mated ­process, experience in the area of ­positioning is required. Generally, dynamic, sensitively controllable EC ­servo motors are particularly suited for such tasks. They allow for any length of movement path, limited only by the technology of the remaining devices, and offer high performance with compact dimensions. Even very different types of measuring devices can be tested in one and the same testing device without any problems.
In this case, an EC Sinus servo motor with an output of about 100 W and an ­integrated transmitter was selected. In this manner, the testing device ­computer receives 3000 increments per motor shaft rotation. One increment therefore ­corresponds to an angle of only 0.12 degrees. This angle is further ­broken up by a flanged planetary gear at 134:1. The gear output then ­engages the spindle drive with repeated gear ­reduction for the sleeve. In this manner, an adequately high transmission amount is reached in order to also safely break up the smallest movement paths of the sleeve. Since with such small paths the mechanical clearance of the gears must also always be taken into consideration, the ­testing device always moves the plug gauge of the test item from the idle ­position into the
“0”-position in order to ­eliminate this clearance. From the zero point, the measurement is then started free of any clearance.
In order to relieve the test computer, the EC motor runs with its own internal controller. In this manner, only simple ­control commands are necessary with regard to the testing device control, the rest is done by the drive itself. This also relieves the quick integration into the device, any special work knowledge is not necessary for this.
Today’s small drives with electronic controls offer high performance in the smallest of spaces. Thanks to the inte­grated controller and incremental ­encoder, they are also easily integrated into total systems. Despite of this, they allow both extremely precise positioning, and quick dynamic movements, and if required by the application, even in 4 quadrant ­operation. If the drive ­specialist FAULHABER is integrated with his know how at the beginning of the development, remarkably efficient and yet inexpensive drive solutions can often be established.