Crank slider mechanism with constant movement

Hello,

i want to drive a crank slider mechanism with a stepper motor. The mechanism would have to push at its end a block with a constant force.

The problem is, that the crank slider mechanism has no constant output force when the input motor torque is constat.

As the result the input motor torque has to be not constant and depend from the angle of the angle of the mechanism.

Is it possible to drive this system to push the block with a constant force?

Has someone made something similar?

Thank you in advance!

Perhaps you could give us unitiated a picture of a crank slider mechanism.

Paul

In the attachement you can find a sketch of the system. It is a normal crank slider crank mechanism. My aim is a constant force F. Thatswhy i would like to know is it possible to reach this through the control of M1 torque?

The motion is in horizontal direction. The gravitiy should not account.

Crank Slider.pdf (155 KB)

Just looking at your diagram you can see the “force” is proportional based on the angle between the two arms at pivot point B.

Paul

I know this dependence. My question is, is it possible to control the torque M1 in such way that the force F will be constant. For example M1 will be dependent on the angle of the point B. Or is such a controller not possible. The motion should be slow (1 - 7 rpm)

Can you accept the fact that at two points, the force will be zero?

Paul

A stepper has uncontrolled torque. Only position is controlled. If you need fine control over torque then you need a different motor.

Whould a servo motor with a gear box work?

I can accept, that at two points the force can be zero, because i do not want to head for this positions.

villagepete:
Whould a servo motor with a gear box work?

I can accept, that at two points the force can be zero, because i do not want to head for this positions.

Would have been my first choice.
Servo already has a gearbox ( among other things)

I am thinking spring from B to plane P would exert a assisting force where needed as long as you rotate motor forward and backward instead of continuous circle.

My question is can be the motor torque be regulated in such way that the output force will be constant?

The servo arrangement will regulate itself up to maximum rating of the servo.

Reason being it is a geared down permanent magnet motor of relatively constant speed.

Usual rating is Kg/cm and for a standard rc servo the maximum applied voltage is 6.0V.
If you look you will see there is also a speed spec that is covered as long as you are within the load and voltage limits.

Meaning as you go further out on the supplied servo arm it can push (X)kg from (X) cm out from the pivot centre of the arm. Only thing that will change(minimal) is the speed of the slider as the arm motion creates and arc travel.

Why don't you simply try one and see instead of getting bogged down in all this imaginary theory that will never be disproved anyhow.

bluejets:
The servo arrangement will regulate itself up to maximum rating of the servo.

Reason being it is a geared down permanent magnet motor of relatively constant speed.

Usual rating is Kg/cm and for a standard rc servo the maximum applied voltage is 6.0V.
If you look you will see there is also a speed spec that is covered as long as you are within the load and voltage limits.

Meaning as you go further out on the supplied servo arm it can push (X)kg from (X) cm out from the pivot centre of the arm. Only thing that will change(minimal) is the speed of the slider as the arm motion creates and arc travel.

The speed is not important, it should be about 1 rpm, variation is accepted. For me is the constant torque throughout the process very important. It should be possible to adjust the force. For example i put a value 100 N into the programm on the laptop and the control should adjust the needed torque for the constant force.

My question: Is this possible and how can the controller can be realized?

bluejets:
Why don't you simply try one and see instead of getting bogged down in all this imaginary theory that will never be disproved anyhow.

At the moment i am in the planning phase and do not have the crank slider mechanism.

As I said before, the servo motor will simply draw more current should the load increase, up to it's specified load/voltage rating.

If you bother to do some experimenting with the servo approach you will soon see the speed of transition is up to how fast you decide to change the pot/variable signal level.

Look up the tutorials on servos and try it for yourself.
Kindergarten closed for the day.

An RC servo, like a stepper, allows you to control position without regard to force. The servo applies whatever torque is necesary to reach the commanded position. (Of course torque is not unlimited; each servo has a maximum output.)

A brushless DC motor with an appropriate controller could do this. But it will only be possible to keep torque regulated over a small part of the motion. The motor will have both maximum and minimum torque limits. If you need 2cm output travel then you will need a crank arm of at least 4cm, which would be capable of 8cm total travel.

OIC your question.
“For example i put a value 100 N into the programm on the laptop and the control should adjust the needed torque for the constant force.”

Sounds like you will need a load sensor to detect how much force your outputting and then something like a PID control to adjust power to the motor.

Slumpert:
Sounds like you will need a load sensor to detect how much force your outputting and then something like a PID control to adjust power to the motor.

As already covered, not necessary with an rc servo driven within it’s specs.

bluejets:
The servo arrangement will regulate itself up to maximum rating of the servo.

Yes. So how do you command a specific speed or torque or force for the servo? The only control you have is position. Speed can be adjusted by simply providing positions corresponding to the speed you want but you have no control over how fast the servo moves between those positions.

There is this........