hydraulic actuators

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Joined: Sat Jun 25, 2016 12:34 pm
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hydraulic actuators

Post by iconoclastica »

Even though I am still happy with the recent progress I made with hand sectioning plants, I can't stop my thoughts thinking of possible improvements.
The least predictable factor in the process is, in my short experience, the feeding rate of the sample to the knife. I know push forward the sample with my index finger. Several options (stepper motor, micrometer screw) were rejected while I cut within a water filled tray.
One posibility that crossed my mind is syringe hydraulics: two syringes, connected by a tube. When the active syringe is pushed in, the passive one extends by the same volume, at least when the passive syringes volume is greater or equal to that of the passive syringe. For an experiment, I connected a 1ml syringe to a 24ml one. Pressing the active syringe for 5cm very smootly extends the passive syring 3mm, a 1:16 ratio. A stepper motor would do 400x50 steps when driving the system with a standerd thread, so plenty of play for choosing the stepsize. A sufficient length of tube will isolate the electrc parts from the watery working area.

Now I didn't start this topics for to ask for practical solutions. It almost seems easier tried than asked. But I do wonder why I haven't seen hydraulics here before. At first sight it seems much simpler than mechanics to realize micrometer-range movements. Also much less cost intensive.
There are other considerations, though. Compressability of the hydraulic fluids isn't one of them, if I understood my quick introduction into hydraulics well. Water performs equally to technical oils and the latte compresses roughly 0.5% per 1000PSI - my system would explode much before reaching hat pressure. Glycerol performs in this respect twice as good as water. Less confident I am about the elasticity of the tube. Today I used the first suitable tube I found laying around, which is a 1 meter long probably silicone tube. There 's room for improvement here, I suppose. What makes me especially uncertain is how smoothly the actuator really moves. To the eye its does, but perhaps on micro-scale it is much more jumpy. Also, there's hysteresis in the system. It might be due to the elasticity of the tube, or to the one left air bubble, or the quality of the passive piston. But on change of direction there is slack. From the size of the air bubble I can see the pressure changing before movement sets in.

I wonder what (im-)possibilities you see.
--- felix filicis ---

Posts: 123
Joined: Wed Oct 05, 2011 5:05 pm
Location: California, USA

Re: hydraulic actuators

Post by genera »

I'm pretty sure I've seen both Narishige and Leitz / Leica micromanipulator actuators discussed here.

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