Sample changer hack

Posted at 2015-12-18.

Sample changer outside
Sample changer, mostly back together

Tarlab has a rescued Gilson medical(?) sample changer robot lying around. I decided to take it apart and see if the XYZ movements and possibly other bits could be repurposed. There's an included old note that it doesn't move when power is switched on.

Most things bolt together with flat head M3 screws and are laid out pretty logically. A linear power supply, power card of some sort, processor card, and a little adaptor card after a ribbon cable in the moving arm. The processor was an 8085 IIRC with some EPROM and SRAM and IO expanders.

Power components
Heatsinks with transistors and ICs

The power card appears to carry some discrete half bridges built out of BJTs (three BD201/202 NPN-PNP pairs). I'm guessing since there's three motors and three pairs. There's 78/79 pair of linear regulators for +-12 V supplies and I presume an amplified Zener plus filtering for logic.

The interesting part is a ribbon cable leading to the moving head. Head has simple DC motors and position sensors. It should be easy to use this interface to run the motors. I disconnected the motors and spun them around with a lab PSU. 10 V gives sluggish movements and 24 V is quite quick. Timing belts are used for movement and everything appears to be in working condition. The half bridges should be able to give + or - 12 V or perhaps around 15 V unregulated and no more. H-bridge would deliver +- 24 V, but would require more transistors.

Head card
Interface card in the moving head. Connectors for XYZ motor and pots plus LED and ribbon to power card.

There's also a LED and it looks like two TL431 voltage references that set the ends of a set of multi-turn pots used for position feedback. Slightly odd arrangement, but it might have something to do with scaling or whatever you have to do to interface analog inputs to an 8085.

We were unable to find any data on the Maxon motors (DC, brushed, with 30:1 gearbox, evidently) except a few similar models for sale and/or queries about their data and availability.


Build some bridges to run the motors and see if the feedback can be used as-is or rewired for a modern micro with ADC's.

The power supply is also quite serviceable, if old, and keeping it intact and replacing only the regulators, "brains", IO, and servo electronics with new stuff looks like the way to go.

But what could it be used for? Some (crazy?) ideas:

Let's see how the positioning and coordinate drive (or controlled speed drive) works with this kind of motor.