Re:Digitizing

>Message: 25
> Date: Sun, 07 Jan 2001 23:16:00 -0000
> From: "Gordon Robertson" <Smoke@...>
>Subject: Digitizing

Your process is identical to that I am planning to develop for my own scanning here. However, I do not trust the accuracy of the Z spindle axis, nor my ability to grab the actual coordinates, in my machine. I do think that I can(read may be capable) configure it to output a signal when it is in position and to wait for another signal when a measurement has been made. I also think that I can use a digital indicator or other linear measurement device to collect the coordinate when in Z position. At 9600 baud this would be just a couple of milliseconds, and probably take less time than the reversal in direction. The X-Y values are in sequential order, based on the array that you define for the X & Y scanning pattern. I plan to write a macro program on my Allen-Bradley 8400 that will take simple parameter values for the X & Y ranges, and some kind of step distance along the X axis. Because of the fact that I can rapid down to the measurement plane, rather than feeling my way in at feed rate, I think I can make an immense improvement in scanning time. I also plan to look into setting multiple zones for Z height so that if I have an indicator with 2.3 inches of travel, in some areas I can clear .25, in some .5, and in the rest 1.5 in Z. I already have a .5 inch travel Mitutoyo indicator with SPC output, it should be very good for things like coins and small detail parts. I may purchase that Sony that I found because it is so easy to program the RS232 port on an IBMPC.

>1. The user would plot the area to be digitized thru the simple
>expedient of using jog buttons. This would indicate the starting (0-
>0)and ending (#-#)points of both the X and Y (or A) axis. The
>maximum up and maximum down positions for the Z axis can be set at
>the same time. User also enters the desired resolution. The program
>then creates an array based on the desired resolution and the area to
>be digitized. The X & Y or X & A parts of the array would be
>automatically filled in.
>
>2. Program start would initially move the probe to the 0-0 position
>with the probe in the home (full up) position.
>
>3. Digitizing begins with a rapid Z move to the maximum up postion.
>
>4. The probe now down feeds until the probe contacts the part and
>breaks a circuit. This provides the Z dimension to be placed into
>the array at position 0-0. The probe is returned to the max up
>position.

This is the step in which I will differ. Because I'm going to use a spring loaded digital indicator, I can rapid to position, don't have to worry about crashing the machine or the probe, and then I will:

5) Send signal to PC to read Indicator
6) Interrogate Indicator for current value in Z.
7) Signal Control to continue after signal is read.
8) Proceed to next position by rapid up to clearance plane, rapid to next point, rapid down to measurement plane.


Best Regards, Fred Smith- IMService
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