Z axis stage capstan driven

Hello guys I am working on a z axis lift driven by stepper to lift and lower the platform precisely . It will be driven by a capstan drum fixed to stepper shaft and cable routing around pulleys . I have a stepper nema23 with 1n-m holding torque . As per my calculation toque required By motor to lift the stage would be FXR since I am looking to design the stage for max payload of 10 kg I assume the motor torque is sufficient but as we know the efficiency of motor is actually less assuming 80% available torque would that be enough since I am running cables through capstan drum with 2-4 wraps and around pulleys will I be having some mechanical advantage so that my motor is capable with available torque? If yes will that be sufficient enough to hold the stage if there is a power failure without slipping I am routing cables similar to this diagram Patent US5273352 - Load-distributing platform transport apparatus - Google Patents I also thought of increasing torque with torque amplifier design Torque amplifier - Wikipedia, the free encyclopedia is this feasible enough . Waiting for valuable suggestions

Please help guys looking forward for suggestions I would like to add this stage is for a engraver/3d printer combo and the bed size is 2.5ft x 2ft I want this to be driven by cable drive instead of lead screw or threaded rod I want to try out this concept first

I think here you can find the required solution.

http://cncmachinetools.org/what-is-a...c-servo-motor/

Thanks for the reply but the link doesn't answer my query as you can see my basic concern to drive the stage with capstan driven by stepper and lift and lower very precisely and when the power is cutt off stage doesn't drop to bottom

Did you consider the mechanical advantage of the capstan's radius? Also, does the motor have a "power-off" brake in case of power loss?

Dick Z

Hi Richard the motor is a stepper which is connected to a capstan drum of diameter 0.035m the stepper doesn't have any power off brake which is the same reason I wanted to design a system so that when the power goes off it doesn't drop as I mentioned in my post I was looking to design a torque amplifier where the stepper shaft is connected to capstan drum which is wrapped with a cable and passes around two pulleys one of them is a output shaft and I connect my another capstan which drives the z axis mechansim to this output shaft I was thinking since there will be more torque available at output shaft will that be enough to hold the stage from dropping off when the power goes down ? I am open to advises as I want to develop this system and make it work

The capstan drum diameter is .035m? (1.38 inches) Without power, the motor has no holding torque.

Dick Z

Richard the stepper has a holding torque of 1n-m i am driving the capstan drum like similar to the attached image Attachment 247712 I am driving lift mechanism from the output shaft of the above image in which u can see it's connected to pen slider . If I follow this setup wouldn't this produce enough holding torque coz what I read is torque amplifier amplifies input torque 2-3 times for your refernce I am again attaching the cable route system I am following Attachment 247714

The motor has 1Nm of holding torque when it has power. It has zero holding power when the power is interupted unless it has a power-off brake. That said, you may have enough friction in the mechanics to hold the load but I woild not depend on that to be true. It appears in your attachment that there is a gear box of some sort that the motor is attached to. If that gearbox is a speed reducer it will amplify torque by the ratio of the gearbox X the efficiency of the gearbox. Or you could simply counterbalnce the mechanical load.

Dick Z

Thanks a lot for the suggestions I thought the same that I may get away with the friction holding the stage but I want this to be a robust solution as you said gearbox can increase the torque but since I do not have one I was looking for alternatives and while I was researching I happend to cone across this term "torque amplifier " in mechanisms handbook where it was described to increase output torque what I want to know is if I want to increase the torque by this method is it going to work ? The other option I was thinking was to achieve some gear ratio in form of belt pulley like driving with small pulley attached to large pulley which then drives the capstan mechanism I can add counterweights and throw all the above out but I have some space constraints I don't know what should I really use as a counterweight material looking forward for your repky

For a torque multiplier you could have a planetary gear system inside or below your capstan drum. You might also place a second capstan drum above the existing capstan to operate an added counterweight section.

Dick Z