Todays Project - What did you do today?

[TomG]

Finished up a little project at work today that I've been working on for a month or so. It's a manufacturing tool for producing a disposable used in one of our products. The disposable is a standard 96 well microplate (talking biology here) that has microscopic scribed lines on it used as reference points for an instrument we build. The lines are about 5 microns wide (.0002"), three on one axis and one on the other, and cross in the center of each of the 96 wells. They are produced by dragging a ceramic blade across the surface of the plastic plate at precise intervals. I built the first pair of these monstrosities about ten years ago, and production has grown to the point where manufacturing can't keep up, so I did a redesign to include faster, more modern motor controls and an overall larger frame. These two scribers should increase production by about 70% and eliminate the aging and troublesome electronics in the old devices. I don't get involved in electronics and programming that much, but all the usual suspects were too busy, so I took on the project myself. The mechanicals were easy. It's just a carriage with a fence (not shown in the video) to hold the microplates (8), riding on 1" diameter Thompson linear shafting and driven by a large stepper motor via a timing belt. The frame to support everything was made up of 3"X6" 6061 rectangular tubing. The scribing mechanism itself is being reused from the old devices to save time. It is basically a THK linear slide holding a ball bearing pivot with and arm to hold the blade and a rotary solenoid to lift it. It also has a damping mechanism that I designed that uses eddy currents from a ring of rare earth magnets acting on an aluminum disk. It helps to prevent chatter as the blade drags across the plastic surface. The stepper motor controls and the software to run them are from Applied Motion and they work very well. They each have a 100 line program capacity and are responsible for different axes. I made the one for the Y axis a master and the X axis or carriage control is the slave. They are linked together via inputs/outputs in a handshaking arrangement. Basically the Y axis control is responsible for the line spacing on the plates and the X axis control moves the carriage when the blade is in position. It's pretty cool watching the two separate programs communicate with each other on the computer screens. The computers are just for writing and debugging the programs. Once that is done, programs will live in the controllers and the scribers will be stand alone.

Anyway here's a little video showing the one of them in action. The whole debugging thing went much better than expected. I loaded the programs yesterday and had it all working as advertised by lunch time today. I did have one of the software dudes help solve a couple of stubborn issues, but overall it went very well. In the video, the red button has three purposes. A short press homes the X and Y axes, and a long press starts the scribing cycle. The toggle switch selects rows or columns on the plate. The 8 rows each have a single line in the center of the wells and the 12 columns each have three lines spaced .11mm apart. A third press of the button during the scribing cycle will interrupt the program and park the blade at home.

Tom