rotational motion to oscillatory linear motion

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Building a project and I need some ideas for converting the rotation of a DC motor into oscillating linear motion (i.e. a back and forth motion). To be specific I need about 2-3mm of travel in the mass I'm driving back and forth, the frequency would range between 50 to 150 Hz, and although I don't know the force I need yet, it's not all that much (but more than you would be able to stop with your hand, if that helps). Okay, so I just use a cam, right? Here's my special requirement though: I want the linear motion to be along the axis of the motor's rotation (i.e. point in the same direction as the motor shaft). So a simple plate cam is out because that can only give me linear motion in the plane perpendicular to the motor shaft. I've been looking around and a drum or cylindrical cam would seem to do the trick, but I was wondering if anyone familiar with this sort of thing knows of a better way to do this? Thanks.

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Does it need to be colinear with the motor shaft, or is an offset acceptable?

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Variable stroke Hydraulic pumps use what I know as "squash plate" cams. There are two versions, one which uses a round cam "disk" mounted on the shaft so that it can change orientation from perpendicular to the shaft, through an angle of about 15 to perhaps 20 degrees from perpendicular. By varying the angle from the perpendicular the stroke of the cam follower can be varied.

Another variant has the cam lobe machined on the cam plate in the same direction as the shaft. Once again the follower runs parallel to the shaft.

HTH, Ernie

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Ned Simmons

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"swash plate"

Ned Simmons

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In addition to the excellent responses generated so far, you have these other options:

1. A solenoid that you feed a sine wave. (Think voice coil) - Low friction, no mechanical linkage to wear - You can even apply feedback to the control loop if you wish.
2. Linear actuator.
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There is a grooved cylinder that provides one cycle of linear motion in the shaft axis per TWO revolutions of the shaft. This depends on a shoe riding in the groove that is longer than the groove's width, so that where the track crosses itself, the shoe continues in the appropriate track.

Brian Whatcott Altus OK

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Preferably colinear, although I'd be willing to entertain ideas with a small offset.

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My original thought was to use something like a solenoid, but I worry about the fact that under continuous use the heat build up will degrade it. Also, it'd be nice to have a guaranteed length of travel in the linear motion without having to add a sensor for feedback control. I think some of these same concerns apply to a linear actuator as well plus I haven't really found any electromechanical devices that seem to fit the bill as far as what I need.

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Perhaps you are looking for an adjustable cranck mechanism. I made such an invention called the Variator. Please take a look at