Controllable Force & Speed Linear Actuator

[Eubie]

I am investigating linear actuator technologies as an alternate to using pneumatics. I require independent control over both the output force and stroke velocity. The force needs to be varied between 30-160N and the stroke velocity varied up to a maximum 1.2m/s. The maximum frequency of actuator movement should be 16Hz. The stroke length should ideally remain the same at about 15-20mm.

Any suggestions of anything that could provide this. I have been looking at electrical actuators but I don't know that its possible to independently control both the output force and speed.

 

[Pkruse]

I'd suggest dropping the concern for controlling force. Don't think of the actuator applying a specific force. The load will provide the force and the actuator will match it. You only need select one that has the ability to provide a safe margin over the max force provided by the load.

Output force and speed are related parameters that cannot be controlled Independantly. Pick one or the other to control, and let the other follow. I suggest speed.

Now you only have to consider required speed and controllability. You have many choices, but we would need to know more about the application to suggest more.

 

[Eubie]

Thanks for the reply. The problem is that the current system seems to cheat a little by using the pneumatics. The output force can be increased by increasing the pressure and the frequency of the actuator movement is dictated by a solenoid valve allowing air into either side of the cylinder chamber. Analysis shows that the speed of the stroke stays roughly the same despite the changing pressure.

My task is to create a similar system and from what you have said it would be best if I could control the force output between 30-160N and if at all possible maintain a relatively steady stroke speed.

 

[tygerdawg]

Your description is a little confusing.

• Do you require an actuator to function as a ram or hammer, impacting an object with different speeds and/or forces? Then halting its motion?
• Or more simply a device to push against an object with a specified speed and/or force?

In either case you could use a ballscrew affair with a rotary servo motor. Or perhaps more simply with a linear servo motor. With a reasonably sophisticated servo controller, you could monitor the motor current. The motor current is generally proportional to motor torque / force. It would require significant engineering to get everything sized properly and then calibrated for force/speed/current, but it could be done. I've done something similar: monitoring the linear servo motor current to detect contact with an object.

 

[Eubie]

It is to be a ram that would impact an object with different speeds and forces. The piston would come out and impact at a specified force.

Would increasing the torque, which would generate a greater force, drastically reduce the stroke speed?

 

[tygerdawg]

Not necessarily. Most likely you will only get a definitive answer for that question by examining a motor's speed/torque curve data.