Sunday, October 29, 2006

 

Cranking up the y-axis positioning stage...

My South African guest left Thursday, so after a few days of catch-up I have a little time to work on Tommelise.

The Austria Microsystems magnetic shaft encoder chip (AS5035) is super handy in that the activating magnet will stick very firmly on the end of your studding shaft. I took my little poplar mounting board, put it up against the magnet with the bottom edge firmly against the baseboard of the shaft and guide rod mounts and gave a tap on the back of it with a heavy screwdriver. This marked the board with the magnet's position. Bingo, automatic alignment. :-)


Centre the chip over the magnet-shaped mark and paste it down with a little blob of silicone sealer and you are set. Two more blobs plus an ear swab will set the filaments on the board and take them to the edges. It ain't pretty, but it works quite well.

After the silicone hardens, a few pieces of thin carton (cardboard) for shim, a c-clamp and we're good to go for hookup.


Actually, putting a hulking huge c-clamp on the edge of a thin piece of poplar made for a rather fragile join, so I glued it to a block and then clamped the block. That worked much better and gave me something to secure the transfer wires to.


I have a 16F877A prototyper board built up which can handle two motors, so I went from there after installing new spike-suppressing capacitors. After that I checked it out system by system till I demonstrated that it can do PWM control of motors and directional control.

One of the things that I noticed that took up a lot of board space was the fact that the Hamamatsu limits detector and the Austria Microsystems magnetic shaft encoder chip were both remote from the board and also required both 5v power, ground and a variety of resistors and capacitors between both signal lines and power input lines as well as lines from various pins to ground with components in between. If you put all of this nonsense on your controller board you quickly found that you used up all your room to not too much effect.


What I did then was to create a 5v power supply board and common ground over on the other side of the work surface near to where such chips were physically located. Such component laden lines from chip pins to ground and such not I ran to this board rather than the controller board. That let me limit lines going into the controller board to the conditioned signal line only. This greatly reduced the space requirement and improved access to microcontroller ports for those chips.

With the Austria Microsystems AS5035 chip there is a 1 uF capacitor between the 5v power input (pin 16) and ground and a 100 nF capacitor between pin 15 and ground.

Here you can see the two capacitors hooked up and blobbed in with silicone sealant. The orange wire in front of the 5v power line (orange) and the ground (black) carries the encoder signal (pin 3) back from the chip to the 16F877A on the controller board.


Here is a view of the same encoder chip block from the front side that faces the magnet on the studding shaft.


Here I have hooked up the remote power board to power and the encoder block and am checking for pulse generation.

Note that we always know which direction that our motor is moving in, so we only need pulse signals off of one of the shaft encoder phases, not both. That is why we only use pin 3 and not both pin 3 and pin 4.

Seem to have picket up a short in the encoder mounting block. Sometimes I get good signals off of it and other times I don't. The chip seems to be taking on too much amperage. It shouldn't be warm at 2 mA.

In progress...

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