Automatic Calibration and Simulation Frame For KRAB Measuring Trolleys
The idea of manufacturing an automatic calibration stand arose from the need to smoothen up and refine existing calibration method of KRAB (and similar trolleys) as all the equipment in use should be calibrated regularly at yearly intervals. On top of that the frame also allows simulating the passage of KRAB through the track.
Stand frame is composed of the upper part, on which the trolley stands on, and lower part, which lies on the ground. Both parts are connected with joints. This connection allows the upper part tilting relatively to the ground and thus setting the cant. Because the trolleys are produced in gauges ranging from 750 to 1668 mm, corresponding mechanism allowing this range is used on the stand. Variation of top and alignment is provided by a mechanism with two degrees of freedom. Movement of twist arm is provided by a special mechanism. All moving mechanisms are implemented using hybrid stepper motors. These stepper motors allow setting up to 10000 steps per revolution thus their running is very smooth. Conversion of motor momentum to linear movement is provided by belt drive and ball screws.
Calibration program works in two modes. The first mode is the control of individual axes, which is intended for manual calibration using KRAB’s PDA, so the movement to desired position is controlled by user. The second mode is automatic calibration, which takes place in the following steps: Stand is driven to preprogrammed positions. The positions are programmed to form a closed loop. In each location data is retrieved from KRAB sensors and stored into PC. After the cycle is complete, calibration constants are calculated on the basis of stored data. Calibration protocol in MS Excel is generated on one mouse click using ActiveX.
While the simulation program is running, Krab trolley is in acquisition mode. Stand performs the signals measured in the track or artificially generated signals. The Krab trolley evaluates and records stand behavior. After the simulation is finished, verification can be done by comparing the recorded and performed signals. This will reveal errors on tested trolley, if there were some.