Hi folks,
I have designed and built a simple Pendant for use with the CNC machine I am building.
It uses discrete parts, so as to make for easy testing during development.
A stepper motor is used as a carrier for the jog wheel and the optical encoder disc. The stepper motor has another use too, it generates a very pleasant degree of tactile feedback when turning the jog wheel.
I thought I would include my circuit diagram here, so folks could take a look and suggest possible improvements / weaknesses.
There are pictures of the completed device in the photo callery.
It's quite a small unit, so it fits nicely in my hand.
I need to use both hands to operate it. This helps to keep my digits clear of the moving machine parts .
The 4 axes can be driven at the same time, but will all go in the same direction - since there is only one direction control coming from the Pendant.
Single axes can be selected by pressing the appropriate switch while delivering pulses from the 2 possible onboard sources.
1) A variable oscillator provides 'auto pulse' mode (200Hz to 6000Hz),
2) An optical MPG provide 'manual jog pulses' when the jog wheel is turned.
The MPG has a velocity control switch to select between full jog speed and 1/64th of full jog speed.
This comes in handy when making final adjustments to the positions of the various axes.
Direction control comes from the jog wheel. Its last movement dictates the direction in which the axes move when driven in 'auto pulse' mode.
When the Pendant is plugged into the mill, the computer detects its presence and halts the program, if it was running.
This function is afforded by the 'Computer lockout' pin on the connector. Its purpose is to prevent the two sources of motor pulses from interfering with each other.
The Pendant has to be unplugged before the computer can resume control of the machine
This design is not perfect, as it is possible for the 'auto pulses' to be delivered while the 'manual pulses' are being generated.
A bit of extra circuitry could have fixed this, but I figured it wouldn't be too bad .
If I were to do this again, I am sure I would opt for a PIC Micro.
This would save on parts and make for a much more versatile device.
Best wishes,
Steve-tee.