I am looking to build up a Simplex Regular/Standard with an electronic intermittent (for fun), with an electronically controlled LED light source to eliminate the mechanical shutter. I am looking at three different possible drive systems: Open-loop stepper, closed-loop stepper, and BLDC motor. Since the sprocket will rotate 90 degrees every frame, any positional error (due to eccentricity, encoder accuracy, feedback error-correction, and motor pole construction) between the four positions would cause vertical jitter (I'm assuming direct drive for the motor). The BLDC motor also has the issue that the rotor does not lock at rest, although claw pulldown transports don't either (but some cameras have a registration pin). I'm wondering if anyone has any suggestions, and what kind of drive Phillips used in the electronic intermittent version of their projector.
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Kinoton used a servo with an encoder for position feedback on their E-machines. The resolution of this encoder depended on the model/generation, but I believe the older ones were 13 bit, which is enough resolution divide 1 complete rotation into 8192 pieces. -
Back in the 90's I had an RCA FR-35B 35mm projector with electronic pull down. It could do 3:1, or 5:1 pull down by changing a jumper. The one I bought came from Editel in Chicago and was used for film transfers. I eventually sold it off, but I do have pictures and a couple schematics that I will post in the next day or two...Comment
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RCA and Kinoton used servo drive Magna Tech, Eprad, CFS and Westrex were stepper motor drive intemitentsComment
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In my automation projects i use control techniques motor drivers and there bldc servo motors. Holding down for bldc motor will not be a problem, since holding torque is higher in holding than in mowong for most of servos. I wanted to built same system for fun, and even did some test on my bench. Master encoder was mentioned to be some encoder on projector transport sprocket, and slave would be servo. I've had some EnCos servo and 4096ppr incremental as master, which should be suggicent. I was working on table, but newer get chance to try it out.
What components you plan to use?Comment
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Thanks all for suggestions and information. This is probably a way-in-the-future project, but who knows? I'm hoping not to need to invest in an industrial sized motor and driver. My thinking is one motor for the intermittent, one for the other sprockets, and a couple of torque motors (which I have), for the reels.Comment
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Basicly i tought to go like this, cell it is like kinoton system. Both sprockets for in and out are driven with same motor over belt. There should be encoder for master position, so that intermittent and shutter motor can be sync to it. I think kinoton used servomotor with 6000rpm and 0.5nM or something similar. And shutter was driven by some stepper if i am correct!?
Check out Control techniques M700 or smaller M750, even 0.37kw should fit need and built in motion controller could do the trick for whole ibtermittent movement.Comment
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I’ve never used or even seen an electronic intermittent, but design wise, I expect being able to have the resolution to program an acceleration and deceleration curve into the pull down is important for being as kind to the perfs as possible, unless it is also achievable with very low gate tension methods?
Is a tensioned gate even necessary if you have to synced electronic sprockets on either side?Comment
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The RCA I acquired had vertical registration via sensors in the gate that looked at the perfs. There was an on - off switch for that, and it often helped. But if it's a print that was made at high speed that had printed in bounce, then it didn't mean a thing.Comment
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Here is Eprads PatentComment
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As others have said, there were two types used in the past:- Kinoton's EC (and then the rest of the "E" range, as well as clones like the Sondor Nova) used a servo. They claimed this gave them much better precision and control compared to a stepper.
- Others (off the top of my head I know of the Magna-Tech PR-135 and PR-635) used steppers. I have never seen one in person, so cannot comment on Kinoton's claim that a stepper was worse than a servo for image quality, but the logic makes sense to me.
I have spoken to a couple of friends about the possibility of making film projectors with modern electronic intermittents. The motors you need are really quite unique and expensive, but luckily today you don't at least need to go and have them custom made as Kinoton needed to do in the late 80s for the original EC. For the ECII, I think they used an off the shelf motor, with their own control electronics in there. If you want, I can send some photos of the insides of my EC and the motors there?Comment
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The CFS dream machine was a stepper systemComment
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