PCI-7344 Servo Torque Control

[choijs]

Hi,
Is there any body to have controlled torque with PCI-7344?
I have two servos to keep servo's torque constant as a target value. The target torque can be changed on cerain conditions.
So the servo's torque reaches the target, it shoud be stopped at that postion unless any change in servo's torque happens. If the servo's torque is below the target, it shoud be move forward to get more torque and vise versa also.
Now, I would like to know how to use PCI-7344 axis to control torque.

[KenSun]

Hi Choijs,

It's really the motor amplifier that is doing the torque control rather than the motion controller.

Most amplifiers today are current(torque) amplifiers. In addition, a lot of amplifiers can operate in either torque mode, or velocity mode.

Now, the reason why torque amplifiers are also called current amplifiers is that torque is proportional to current. When the motion controller outputs a command voltage, it's up to the amplifier to convert that voltage into current, and it's up to the amplifiers internal control loop to hold that current. Essentially, the amplifier controls the torque via a current transformer. When there is a difference between the desired torque, and the actual torque from the current feedback, the amplifier will adjust the output vo
ltage to accomdate for the difference.

That's probably too much information, but you just need to know that the torque control is actually done at the amplifier level, and when you are using an amplifier in torque mode, all this control is done for you by the amplifier. So, there is nothing the 7344 needs to do.

Another way to think about this is whenever you tell a motor to go to a specified position and stay there (using a torque amplifier). You are doing torque control automatically, since it takes effort to hold a motor at a specific position. The control loop on the amplifier is constantly doing what you have described, without the 7344 knowing what it's doing.

Hope this helps.

Ken Sun
Applications Engineer
National Instruments

[choijs]

Many thanks Ken Sun,
Then is it correct to call functions as follows?
1.flex_load_rpsps
2.flex_load_rpm_target_pos
3.flex_load_rpm
4.flex_set_op_mode ;as position control
5.flex_load_torque_lim ; as target torque
6.flex_start

Repeat step 5 and 6 on the fly.