Bi-Directional Pneumatic Drive

In your place, I'd choose not to allow the gears to become loose, or you may have alignment problems with the re-engaging point, probably meshing the gears and causing premature failures.

Instead of it, I'd use a ratched as you stated, mounted in the gear shaft, and allow the pinnion and rack always connected.

Another option is to replace the rack and pinnion arrangement by a 3 link bar arrangement and ratched in the end shaft.

Thanks for the reply, one thing I failed to mention was that the shaft must be able to free wheel ,This is in case of pneumatic failure the shaft can then be turned by hand.

Thanks

Dave.

Do you want to index a shaft a fixed number of degrees for each stroke of the air cylinder in addition to the freewheeling feature? If this is the case, what is the maximum torque, and degrees of rotation?

The max torque at the hand wheel is 282Nm , the shaft needs to do 12 full 360 degree rotations, the amount of cycles by the cylinder foward and back is not that important as there is around 5 mins avalible to get the shaft to do its 12 rotations.

Although there are some size restrictions on pinion diameter and rack lenght due to avalible space.

I have used a cylinder with the shaft attached to a chain running between two sprockets. One sprocket was simply an idler, while the other one had a one way clutch in it and was mounted on a shaft. The cylinder turned the shaft in extension until the desired amount of shaft rotation was achieved, at which time a separate electric brake engaged and the cylinder was retracted, while the one way clutch on the shaft was merely turning in its unclutched direction.

In this particular application, the cylinder was used to drive a feed roller to deliver a measured amount of material. An encoder on the feed roll shaft provided the rotational information to the PLC which controlled both the cylinder and the electric brake to deliver the desired amount of rotation. This method worked very well, and was also very efficient. this method also has the advantage that you can control total shaft movement to (in your case 12 rotations) precisely without regard as to how many stokes of the piston are required.

The cylinder is aligned with the chain and is arranged that it is located beyond the chain loop in such a way that the cylinder rod passes over one of the sprockets with minimal clearance in order to attach to the chain as close as possible to the cylinder axis in order to keep off axis cylinder rod forces to a minimum.

For your application, you would need to add the necessary parts to reverse direction and allow freewheeling, but this overall approach may offer advantages.

Feel free to contact me here for more information if you like.

Regards, Greg