CONTROLLED AUTOMATION, INC.
ANGLELINE
INACCURATE LENGTH MEASUREMENT - PINCHWHEEL
Pinchwheel measuring systems, by design, are not repeatedly accurate over long distances. This type of measuring system relies on the measuring wheel to be in continuous contact with the same point of the material throughout the entire length. If the material moves exactly 1’, then the wheel must also turn exactly that amount.
Any slippage between the material and the measuring wheel will result with an inaccurate measurement. Mill scale, burrs on the material, or material that may have a bow or twist in it, will cause slippage or misalignment resulting in inaccurate measurement. Material that does not convey through the machine smoothly will have a good chance of being measured wrong. The longer the measured distance, the more inaccurate the measurement will be.
Also, every time you run the same piece of material though the machine (running a test piece), you will more than likely get different measurement results. The surface of the material where the measuring wheel is contacting (bottom of the Vee) is being moved through all of the V-rolls of the machine, being slid across the bottom shear blades, and being measured by the wheel. All of this may change the surface characteristics of that particular piece of material.
1. CHECK THE MEASURING WHEEL MECHANICS.
Tighten all loose nut, bolts, set screws, etc.
Check the alignment of the coupling between the encoder and the measuring wheel shaft.
Check any bearings associated with the measuring wheel.
Check that the measuring wheel shaft is straight.
Check that the measuring wheel is evenly round.
Check that there is not a groove worn in the measuring wheel. If so, move the wheel to the side so material will make contact with measuring wheel at a different spot.
On pinchwheel measuring systems, the pinchwheel mechanics have to be perfect. If there is any wobble or movement in the measuring wheel as it turns, it will not measure correctly. If there is any groove worn in the measuring wheel, the wheel should be moved to the side or it should be replace with at new one.
2. CHECK THE MEASURING WHEEL ELECTRONICS.
Check the encoder.
Check the encoder cable. Look for cuts, kinks, smashed spots, breaks, etc.
Check the encoder cable connector at the encoder end. Verify all solder connections.
Check the encoder cable shield & wire connections in console.
If the marks gradually run longer or shorter with all mechanical problems fixed, the counts per inch can be changed to calibrate the wheel. If the counts per inch are changed and there are still mechanical problems, the machine’s accuracy will be worse than before.
To change the counts per inch for the LEN, program and run a part with a mark near the front end of the part (1" to 3") and a mark 20’ down the part from the first hole. The first hole must be accurate.
The formula for calculating the counts per in (CPIN) is
CURRENT CPIN x PROGRAMMED DIST. (in inches) = TOTAL COUNTS
NEW CPIN = TOTAL COUNTS / MEASURED DIST. (in inches)
Enter the new counters per inch in the constant field LEN, LEN_MOTOR, CPIN1. Run the same program again, with the marks at a different gauge, to check accuracy.
EXAMPLE
1290.0000 x 240 (20’)= 309600.0
NEWCPIN = 309600.0 / 239.75 (19’11"3/4)
NEWCPIN = 1291.3452