back-drivable linear motor?

[subsearobot]

Hey all,
I am looking for an electrical linear actuator... does this exist?
~4" stroke
~5pound force (less may be ok)
highly backdrivable, even when energized and commanded
low speed (1 inch per second would be ok)

I am looking for a response similar to what pneumatics would produce, minus the stiction of seals and noise and compressor...
Does anyone make long travel voice coil actuators?

the goal is a consumer product, but I am in prototyping, so cost is not the first concern here.

thanks for your thoughts

 

[Compositepro]

Rolling diaphragm air cyliders have no stiction, or an air bladder.

https://www.marshbellofram.com/bellofram-pcd/types/bellofram-pcd-diaphragm-air-cylinders/

The problem with voice coils are that they use power constantly to maintain any force.

You could use a stepper motor with screw drive to compress a spring to the desired force. The controller would move the motor to maintain constant compression on the spring.

 

[waross]

Take a look at the voice coil drivers used to position the heads in early Winchester Drives. (PC hard disk drive for the younger members)
See if it may be scaled up, a lot.
Or
Low pressure hydraulics with position monitoring and low pressure relief valves to allow overcoming the commanded position.
Or
Simple and almost off the shelf:
A screw drive actuator with the load positioned by a pair of springs, so that any opposing force greater than your threshold will allow movement by compressing one or the other spring.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[subsearobot]

compositepro, nice! I've used belophrams for a different application. they are great! I am hoping to avoid the need for compressors and vents and mufflers for this project though. I had wondered about the power consumption of voice coils. not ideal, but that woudl be ok for a prototype. that said, I may just prototype with pnumatics, and then worry about how to achieve the result with electrons at a later date...

Waross, the spring-intermediaty on a leadscrew system: I had been mulling that, and it's cool to see it confirmed by another independant genesis! I am going to explore that further, as a plan B.

Is anyone familiar with the actuators that toyota uses for their powered lift gates? they are too noisy, but highly backdrivable, and they appear to have "stall" detection. any idea how they achieve this?

thanks again!

 

[itsmoked]

Small torque motor.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Taking that one step further, if you use small pneumatic cylinders in place of the positioning springs, you can easily set the force needed to depart from the set position by varying the air pressure.
Or, three small hydraulic cylinders in a closed system. Two will be positioning forces and the third may be loaded by a torque motor to vary the pressure.
Bill
--------------------
"Why not the best?"
Jimmy Carter