Looking for linear motion suggestions

jkilroy · Jan 4, 2022

I have a linear motion application that is turning out to be kinda tricky. I need a motion range of around 12" with a variable speed range of .25 ips down to .05 ips. This is a vertical lift application with a total load of close to 100lbs. Basically I need to cover a 5.5" distance in times between 24 seconds and 96 seconds.

I have tried to do this with off the self linear actuators using a variable voltage power supply and at the moment the system is either too fast to cover the entire range, or too slow. This needs to be one motion, no pauses or stops.

gustafson · Jan 4, 2022

Maybe a PWM controller would be better than just variable voltage

Strostkovy · Jan 4, 2022

I haven't run any numbers but it sounds like a stepper motor and a leadscrew would work fine. You need to control them with a variable speed oscillator, and may need an acceleration ramp.

CarbideBob · Jan 4, 2022

Budget? How much of it do you want to build?

Life needed in continuous use/cycling?
Clean room or in the middle of a sandblaster?
One off or a thousand?
Positioning accuracy needed?
Brake needed in power off?
Counterweight possible?
I'm sure I can think of more questions.

Lead screws of various types with motors of various types.
Cable or chain drive with various motors and gearboxes.
Linear motor.
Servo valve hydraulics if the pump already in the system for something else.
Very fancy air cylinder system or air over oil.
Cam or offset throw and shaft sort of like a piston or camshaft in a engine. This commonly used on transfer lines.
Bob

Chip Chester · Jan 4, 2022

A variable speed drill and a 3/8" threaded rod will do it. Finer/repeatable control of motor speed will let you nail the lift duration to the millisecond, if needed. Better rod (acme thread) will let you run it for years instead of days. Guide tracks will give you stability and an opportunity to apply braking if something breaks. Thoughtful answers to CarbideBob's questions will get you started.

mhajicek · Jan 4, 2022

Are you doing open loop or closed loop?

CarbideBob · Jan 4, 2022

mhajicek said:
Are you doing open loop or closed loop?

What is open loop and closed?
If I have a prox at where I want to be at does this close my positioning loop?
Do I need to see all inside the move to be closed loop? Or do I just need to hit a target and that is closed loop?
Is velocity control or the in between move a real concern or just getting to my end point at xxx time?
Any motion profile has get to going and stopping and is not one speed. What if any concerns here?

I am very interested on any and all opinions and options here.
I know some stuff and talk. I am still learning and certifiably not knowing. A place like Motion Gurus shop is not gonna hire me.

There is a motion control profile. A gravity or bias load. There is a desired min and max feed speed and a time to get there.
How to best solve without spending money?
Bob

mhajicek · Jan 4, 2022

CarbideBob said:
What is open loop and closed?

A closed loop system always knows where it is, or at least where it was a couple milliseconds ago. It can add or remove power on the fly to maintain a desired speed under varying load. If it can't do this, you're flying blind until you hit your limit, and the system doesn't even know if it's overcome static friction and started moving.

Trying to do this open loop, you're just guessing at the power needed to travel at the right speed. Even if you do get it tuned right, any slight change in the mass or friction of the system will throw off the result wildly. Controlled motion requires closed loop.

Strostkovy · Jan 4, 2022

A loop becomes closed when there is feedback. Even IR compensation is a form of closed loop control.

I would argue a limit switch isn't closed loop, as it is merely starting and stopping an open loop system.

garyhlucas · Jan 4, 2022

Nah,
You don’t need closed loop for this. A stepper motor can do this easily as long as the motor is large enough to not miss steps. Steppers are really good at slow because it favors their torque curve.

Robert R · Jan 4, 2022

jkilroy said:
I need a motion range of around 12" with a variable speed range of .25 ips down to .05 ips. This is a vertical lift application with a total load of close to 100lbs. Basically I need to cover a 5.5" distance in times between 24 seconds and 96 seconds.

This needs to be one motion, no pauses or stops

There are a number of inexpensive ready made 12" slides with stepper motor drives available on EBAY. One of these slides along with the matching programmable indexer box will do exactly what you want at a low cost. For example this used Parker slide with motor is $80.

PARKER LINEAR ACCUATOR w/STEPPER MOTOR w/Digital Encoder | eBay

The stepper motor indexers can store a number of motion profiles. The profile is described in terms of a ramped acceleration, a constant travel speed and a ramped deceleration. The motion profiles can be selected by sending a simple bit code to the indexer. There are also additional bits to start the motion, change motion profiles midway or to do a quick stop. The full featured indexers can be programed for logic branching operations that may be required when controlled motion includes interlock signals.

The stepper motor and lead screw pitch combination is sized based on your moving mass and maximum acceleration. The stepper motor is selected so that the required peak motor torque does not exceed the motor's torque-speed curve.

The Parker- Compumotor website has a extensive tutorial on how this is all done.

Motion Control Systems - A Complete Family of Motion Control System Products from Parker Hannifin

The project will be easier if you work with a motor, drive, and indexer from the same vendor. The Parker motion control software can be annoying to work with. There are applications where it would be a poor choice. The large number (12,000) of used Compumotor components on EBAY will compensate you for the annoyance..

memphisjed · Jan 5, 2022

Agree with Mr Bob. A limit/prox switch is a closed loop. Encoder count of 1.

atomarc · Jan 5, 2022

No idea what your project entails, but here is a recent project of mine. High lead Acme screw, linear guides and a DC motor.

Stuart

crickets · Jan 5, 2022

gustafson said:
Maybe a PWM controller would be better than just variable voltage

Need feedback from the motor to compensate for the load variance. BLDC and PMAC motors will have built-in encoders, brushed DC would require an external tachometer. Most programmable controllers will allow for RPM (speed) throttle mode (as opposed to torque), and will increase voltage under load to maintain the desired RPMs. Then desired RPMs can either be calculated based on the lead screw pitch and reduction gearing, or just picked through testing.

Neither servos or steppers are necessary for the applications where a thing needs to go from one end to the other without anything in between.

Edit:

I think OP should just adapt one of these :
https://www.precisionmatthews.com/shop/align-z-axis-power-feed/

gustafson · Jan 5, 2022

crickets said:
Need feedback from the motor to compensate for the load variance. BLDC and PMAC motors will have built-in encoders, brushed DC would require an external tachometer. Most programmable controllers will allow for RPM (speed) throttle mode (as opposed to torque), and will increase voltage under load to maintain the desired RPMs. Then desired RPMs can either be calculated based on the lead screw pitch and reduction gearing, or just picked through testing.

Neither servos or steppers are necessary for the applications where a thing needs to go from one end to the other without anything in between.

Edit:

I think OP should just adapt one of these :
https://www.precisionmatthews.com/shop/align-z-axis-power-feed/

There is no assumption of more additional complexity for a PWM motor controller. Just a more predictable speed curve

jkilroy · Jan 5, 2022

Life needed in continuous use/cycling?
25% duty cycle
Clean room or in the middle of a sandblaster?
Around fresh water
One off or a thousand?
Two off
Positioning accuracy needed?
None, this is strictly motion, from open to closed, closed to open, no stopping mid stroke
Brake needed in power off?
No
Counterweight possible?
Yes
I'm sure I can think of more questions.

Lead screws of various types with motors of various types.
Cable or chain drive with various motors and gearboxes.
Linear motor.
Servo valve hydraulics if the pump already in the system for something else.
Very fancy air cylinder system or air over oil.
Cam or offset throw and shaft sort of like a piston or camshaft in a engine. This commonly used on transfer lines.
Bob[/QUOTE]

jkilroy · Jan 5, 2022

Closed loop

mhajicek said:
Are you doing open loop or closed loop?

Closed loop

jkilroy · Jan 5, 2022

You are correct, this is for a variable speed valve actuation. Speed control is the key here, position is not.

jkilroy · Jan 5, 2022

Thanks for those links, unfortunately I can't use 'used' in this application, day job

Robert R · Jan 5, 2022

If this is a day job application, the low cost solution will be a off the shelf linear valve actuator.

Selecting linear actuators for valve automation

The online design guide for the Tolomatic valve actuators can be found here:
Electric Actuator Selection & Sizing

When you consider the time involved, manufacturing costs, and possible liability the ready made valve actuator will be a better choice.

Looking for linear motion suggestions

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