I found this today while researching some drive train information. It’s very detailed and includes interesting approaches to perf sensing, capstan roller design, and more. I haven’t read the whole thing through yet but when I do I’ll come back and post notes here.
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Here is an article about the resulting machine and its inventor: Alaska inventor and his film scanner are in demand in Hollywood
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Jotting down some notes of interest after reading through the application:
Shaping the perf sensing laser
…the laser beam is passed through an anamorphic lens to reshape the laser beam from a round beam to a line beam. The line beam improves the accuracy of vertical registration of the film frame, since it widens the area being sensed and is less susceptible to imperfections in the performation edge."
If anyone knows where to find one of those lenses, I’d love to try one out.
Use of O-rings @ capstan
The capstan drive assemblies include rollers with a group of O-rings along their circumference. The O-rings…by using O-rings, the total contact area between the rollers and the film surface is reduced and physical stress to the film is also reduced.
I had the same idea a while back, and had a design sketched out for it but in the end decided to go with the industry standard capstan. I even bought a whole bunch of O-rings! It’s still a good idea, though. You could do a full frame of O-rings, or just do it at the edges. In the latter case, you might need to make the O-ring roller furthest from the machine adjustable to account for shrunken film. Definitely worth a try in the future.
Use of magnetic field for sensing rotation of tension arm
A magnetic field generator is connected to the control shaft and a magnetic field sensor is positioned in proximity to the magnetic field generator. Through changes in the magnetic field produced by the generator, the magnetic field sensor measures the rotational position of the rocker arm and creates an electrical output signal corresponding to the degree of rotation of the rocker arm.
4K camera used
…the digital camera is a Prosilica GE-1660C capable of capturing images at a resolution of 1600x1200 pixels per image of GE-4900C camera capable of capturing images at a resolution of 4872x3248 pixels, with an exposure time of six microseconds at a rate of up to 34 frames per second
Shutter and illumination timing
…the strobe is fully illuminated for 35 milliseconds but the image capture occurs during the middle of the stone flash cycle for an image capture duration of 20 milliseconds.
Laser sensor used
OPDK 14P3903/S35A retro-reflective sensor from the Baumer Company…a small polarizing reflector in the upper gate portion polarizes the laser beam and reflects it back through the film perforations…
Sensing the trailing edge of the perf holes
As film is moved by sprocket driven systems, the leading edge of a film perforation is engaged by the sprocket. Over time and repeated contact with sprocket teeth, the leading edge of the film perforation may one deformed or damaged by mechanical stress. This damage may become progressively worse with each successive viewing of the film. Since the leading edge of the perforation defines the vertical position of the adjacent image, any inconsistency in the position of this leading edge will cause sequential images to appear to jump vertically…a logic inversion circuit may be used to invert the output from the laser position sensor so that the position sensor triggers based on the trailing rather than the leading edge of the perforation. In this manner, film mayu be scanned without regard to the extent of damage to the leading edge of the perforation while avoiding problems associated with jitter and vertical misregistration.
Use of PID
Drawings of the GUI indicate the use of PID loops to control tension on either side of the capstan.
Use of servo at capstan
Hello,
Thank you for reviewing my patent. Please let me know if you would like to license any of my technology.
Reed Bovee
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I was thinking about using a capstan drive for intermittent motion, and came across this post. The inventor/Mr Bovee claims that reducing the surface area by using o-rings reduces the stress on the film. However that seems to be the other way around.
The unit of stress (mechanics) is N/m^2. Suppose the force on the film comes from the capstan drive itself. This load is spread out over a surface area. So if input force is constant and area increases the maximum stress induced on the film becomes lower. I assume capstan related damage is due to slipping. So I would say a larger contact area as well as minimum pressure force on the capstan is required. I
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Another consideration is the capstan material, and the tension required on the film to hold traction. If the capstan is the made of the same material as the o-ring, I would agree that more surface requires less force (and tension) which would be preferable.
One aspect where the O-ring may have an advantage is the flexible nature of the material configuration (the O instead of the solid), which may then require less tension over the capstan, but I do not know if that would be the case.
One successful example of stop-motion capstan is the Gugusse Roller built, which uses a large capstan (a skate silicone wheel).
I am doing an iteration of the snailscan, using an aluminum silicone encoder wheel as capstan / driven directly by a geared-stepper.
Use of “O”-rings as a transport component is interesting. I have hand-drawn several abandoned notions of a caterpillar gate where “O”-rings would function as drive belts around free pulley wheels at each end much like the tracks of a tank or crawler tractor to hold fragile warped film on the film plane.
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