Quick-adjusting linear actuator?

[some bloke]

TL;DR Summary

I am looking for a linear actuator wich can be quickly adjusted but I don't know how best to search for it!

I am making a project which requires a linear actuator which can be adjusted manually, in a similar manner to those Vices which have the ratchet lever, allowing you to manually push the vice in or pull it out rather than winding it in and out. I'd like the same principle but on a linear actuator - is there an official term for this or am I looking for something I'll need to invent for myself? My google-fu is failing me so far!

Essentially I want an actuator which can "tense" and "relax", either driving or being driven at will. Ideally I want it to be as free a motion as possible when being driven, rather than trying to turn the motor!

For inventing it I was considering the same principle as the ball beaing lock found in socket sets, so the engaged part of the ball screw would retract and re-engage on demand, allowing the shaft to freely move in and out of the actuator. I will also be looking to do weight compensation so the shaft (which will be vertical) can be lifted easily before being locked back to the ball screw - could this exist already as well?

Any help gratefully appreciated!

 

[Baluncore]

A double acting hydraulic cylinder with control by solenoid valves.
If you want higher speed use pneumatics with position feedback.

 

[anorlunda]

@Baluncore 's hydraulic answer was a good one. Here are some more possible answers out of hundreds that are possible.

Worm gear linear actuator

screen door opener, slide the disc to lock in position.

How much force? Enough to move a lego block or enough for a freight elevator?
How fast is fast?

When you ask engineers, use numbers not words.
How much force?
How much speed?
How much cost?
How much weight?
How much and what type of external power?

 

[some bloke]

Thanks for the replies!

I realize I was perhaps a bit vague in this, though my original intent was to try and find if there is a standardised terminology for this sort of action!

Making some rough overestimations for my application, I would be looking to achieve:

• 10kN of force, in tension not compression. Edit - this is the shock force, so the force from sudden engagement or an impact. The load it will need to move will be closer to 1500N!
• 4500mm/s peak driving speed, and perhaps moving around 6500mm/s when being driven.
• Accurate positioning, probably to 0.1mm, though to 1mm might be sufficient. This can be put in tandem if needed and controlled through the motor.

I had considered some way of engaging and disengaging the worm gear but I am concerned that it would not respond fast enough without risk of damaging the wormscrew, or not engaging correctly. The intended application would involve constant back & forth motion, with the actuator being driven in one direction and then driving in the other. The actuator I use will need to be able to run for long periods of time without deteriorating or overheating, though that will also be down to sufficient cooling and oil. It needs to be able to drive in both directions.

I am hesitant to use hydraulics due to the high pressures involved and potential risk of hydraulic fluid leaks, which I'd like to avoid. I'd prefer to have no risk of any notable quantity of fluid leaking from the final design.

Another option I am considering is a chain or belt driven actuator, where the moving block of the actuator can grab or release the belt to become driven. This has the advanage of the belt being continuous rather than discrete, so the block can clamp on anywhere, rather than needing to align with the ball grooves.

 

[Big Pineapple Monkey]

@Baluncore 's hydraulic answer was a good one. Here are some more possible answers out of hundreds that are possible.
View attachment 298324 Worm gear linear actuator
View attachment 298325screen door opener, slide the disc to lock in position.

How much force? Enough to move a lego block or enough for a freight elevator?
How fast is fast?

When you ask engineers, use numbers not words.
How much force?
How much speed?
How much cost?
How much weight?
How much and what type of external power?

I also suggest looking at some of Jeremy Felding's U-Tube videos. His site contains links to other sites that could help with this problem.

 

[jrmichler]

my original intent was to try and find if there is a standardised terminology for this sort of action

Standard terminology for motion control problems such as yours starts as follows:

Peak force: 1500 N
Peak velocity under load: 4500 mm/sec
Accuracy: 0.1 mm desired, 1.0 mm worst case

The peak force needs to be further specified - is it due to friction, is it due to acceleration of a mass, is it partly due to accelerating upward against gravity, or a combination of forces? All of which is why the following is also needed:

Moving mass:
Direction of moving mass (vertical, horizontal, or angle):
Friction force:
Peak acceleration:
Motion profile - is it a simple constant acceleration / triangular velocity, finite jerk, or other:

Typical linear actuators are not capable of the 4.5 m/sec speed you specified. You have a high speed drive, where modern high performance synchronous belts work much better than chains. A good synchronous belt system is the Gates Poly Chain GT belt system. Their catalog: https://assets.gates.com/content/da...y/catalogs/old-pc_carbon_manual17595_2011.pdf. When the servo motor is deenergized, it can be easily moved by hand. Provided, of course, that system friction is low enough.

The belt is driven by a servo motor through an appropriate gear (or belt) reduction. A preliminary servo motor selection, based on some guesses from your information, is an Allen-Bradley MPL-B640. The catalog is at: https://literature.rockwellautomation.com/idc/groups/literature/documents/rm/knx-rm010_-en-p.pdf. The performance curve for that motor coupled with a Kinetix 5700 drive is shown:

My experience is mostly with the Allen-Bradley line of servomotors. A-B is popular in the United States, while Siemens servo products are more popular in Europe. Siemens has a similar servo motor and drive product line to A-B. These servo drive systems will easily meet your 0.1 mm accuracy specification, provided that you do the appropriate design calculations for mechanical backlash and stiffness.

Safety warning: These are powerful systems. They absolutely must be guarded against possible human contact when not locked out and tagged.

 

[berkeman]

• 10kN of force, in tension not compression. Edit - this is the shock force, so the force from sudden engagement or an impact. The load it will need to move will be closer to 1500N!
• 4500mm/s peak driving speed, and perhaps moving around 6500mm/s when being driven.
• Accurate positioning, probably to 0.1mm, though to 1mm might be sufficient. This can be put in tandem if needed and controlled through the motor.

Wow, challenging specs! Fun project.

You probably have considered variations of this mechanism already, but the quick-release and reengagement mechanism from garage door openers seems close (except for the linear speed that you need -- wow!):

https://www.precisiondoor.net/uploads/content/garage-door-opener-emergency-release.png

 

[hutchphd]

Did you specify the throw actuating distance ?