A friend was selling some 200 ounce/inch, 3.5 Amp stepper motors for a great price so I thought it was time to upgrade the taig cnc milling machine. With the old steppers installed, the machine was accurate but slow. Since the old controller couldn’t handle 3.5 amps I decided to upgrade that too. I found a 5 axis controller on ebay for a great price. This controller uses the Toshiba TB6560 stepper driver that can handle up to 36 VDC at 3.5 Amps. I wanted a board with at least 4 axis’ so that I could add a rotary axis to the mill but more about that in another post. I went to the local electronics supplier (Sayal elelctronics) and Parm set me up with a Hammond electronics 24 VAC, 10 Amp transformer (a local manufaturer). I picked up a bridge rectifier, large capacitor, switch, fuse, computer power cord socket and indicator light to complete the power supply. The entire conroller and power suppy were mounted in a computer case.

Transformer, bridge rectifier and capacitor.

Switch, fuse and power socket.

Mounted indicator light and switch.

TB6560 stepper controller board and 200 oz/inch stepper motor.

Power supply and controller mounted in a computer case.

Close-up of computer case.

After getting all of the stepper motors wired to the controller board it was time to start testing. I noticed that the motors started losing steps and stalling out at speeds greater than 20 inches per minutes. I hooked the oscilloscope up to the step line on one of the axis to see what was going on.  Instead of a nice square wave it looked more like a sawtooth because of the slow rise time. This is what was causing all the missed steps at higher speeds. The culprit was slow rise times of the optocouplers situated in the circuit between the parallel port and the drivers. An easy fix was to take the optocouplers out and jumper them with a wire. The parallel port is no longer isolated from the driver chips but that has never been an issue with my other drivers on different machines. The machine can now run easily at 40 inches per minute.

In this photograph, on the left, you can see the waveform of the slow rise time of the optocoupler. The waveform on the right shows  nice square waves generated after the optoisolators were jumpered. This makes a big difference considering that there are 8000 steps in one inch.

Karl P. Williams

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The positive photo fabrication method was used to create the boards. The supplies are from MG Chemicals and are readily available at Sayal electronics. After the boards were designed, the top and bottom traces were printed onto transparencies in an inkjet printer. Because these boards are double sided, vias are used to connect the top layer traces to the bottom layer traces. The transparencies are cut to size and carefully aligned so that the vias on each side line up perfectly. I staple the transparencies together and then slide a double sided, pre sensitized, board in between.

The transparencies and the board are then sandwiched between two sheets of glass and held together with some paper clamps so that nothing can move out of place when the board is being exposed to ultraviolet light. The side opposite to the one that is being exposed to the UV is covered with light blocking plastic. when the top of the board is finished being exposed, it is covered with the blocking material and the other side is then exposed.

I happen to have a UV eraser unit left over from the ‘good old days’ of microcontroller programming and eprom erasing so I use that as my UV light source but a regular fluorescent bulb will also work. Note that I cover the entire unit up when it is operating so that I’m not exposed to UV.

After the board has been exposed it is developed much like a photograph. The areas that were exposed to the UV light are washed away and the circuit board pattern that is left will protect the copper from the etchant during the next step. This is where the whole process can get messy with chemicals. When Darin White completes his board mill we won’t have to deal with this any more.

What’s that cooking on the hot plate? That delicious black tar is ferric chloride, a metal etchant. The ferric chloride dissolves the unprotected copper from the board and leaves the circuit design intact. The solution gets darker as more copper gets dissolved and it takes longer to etch a board. I heat it up so that it is warm and then turn the hot plate off. This stuff has to be put back into the bottle and disposed of at a chemical waste drop off site when it gets saturated.

Etched boards washed and dried.

The boards are then drilled.

Here are two completed stepper motor controller boards attached to the parallel port breakout board. Note that the cables connecting the breakout board to each controller were fabbed out of an old hard drive ide cable by cutting the header on a band saw and splitting the ribbon cable. That saved me a lot of time soldering.

The Robots are coming.
By Karl Williams