Mach3 plugin

Whoever uses Mach3, this strangeful designed VisualBasic program?

A better choice today is using GRBL embedded into an Arduino board (or simply its ATmega328 microcontroller).

The plugin

A Mach3 plugin skeleton without MFC for outputting wave data to a suitable (mostly USB) device. It's not tested!

The plugin opens a system wave device expecting three channels (one for each X, Y, and Z axis) — or more for rotational axes, and will output data with following characteristics:

In opposite to the ready-made SmoothStepper board, no driver installation is needed at all.

How to implement the CNC machine

A microcontroller is obviously necessary. For it, 8-bit types with built-in USB interface, like AT90USB162, are sufficient. For more performance, necessary for parallel kinematics like this one, a 32-bit controller like AT91SAM7S should be used. Also, when encoders and therefore feedback loops (with PI controller) are used, a 32-bit controller should be used.

Motor control

All what a CNC constructor has to do is to create a microcontroller firmware that exposes a suitable USB sound card to the PC, and interpret the incoming data accordingly. Despite the relaxed sample rate (incoming data rata is only 3 kByte/s), the firmware can easily create high-speed, high-resolution step pulses for the stepper motors, because:

For built-in safety, a disrupting waveform data stream will lead to an emergency stop, which is mostly intended.

An emergency stop removes power from all motors and activates all available brakes. The exception from this rule are motors or solenoids holding a load that will otherwise fall down and make additional damage. References are lost, and a synchronization movement is necessary in front of next positioning.

A normal stop speeds down the motors as fast as possible, then holding them for some microseconds to ensure braking, and later reduce or remove power. References are kept.
Incoming invalid data, such as 80h-centered sound data, must be ignored by that firmware, to prevent inadvertent movements by a mis-configured media player.

See also: USB2LPT and CNC

Switches and feedback

All switches are relatively low-speed and reported by an HID interface. This will include all end switches and some human-interface switches, possibly an extra Emergency Stop contact. (Of course an Emergency Stop should interrupt the power supply for all drives – in wired hardware!) This is to be specified!

Construction of controller firmware
The only source for high-speed return data is an encoder. Such data is fed to Mach3 by another “sound” channel (like a multi-channel microphone) in the reverse direction. Also, counts and microsteps are transferred. For stable operation, encoder positions should be processed by the microcontroller, not by Mach3.

Source code

[ICO]NameLast modifiedSizeDescription
[   ]Mach3Usb.zip2013-04-05 13:57 10KThe source codeBrowse archive
[IMG]usbif.jpg2013-07-31 17:20 27KAbbildung (Foto)