Torque Control on componet at different temperatures

Greetings,
I am in the process of building an application with Motion Control with change control modes from position control to Torque Control. Here is my situation. I am going to be twisting a rubber component from +- X Nm's at a particular frequency. However the component will be under temperature extremes and as the component heats up and cools down the stiffness changes therefore it may take more or less angle to achieve programmed torque. I still have to keep my frequency unchanged during the transition though. Is there automatic error compensation for velocity to keep the frequency unchanged even though the distance required to achieve Torque setpoints will change? I hope this is Clear enough to get a handle on what I am trying to achieve. I have no problem with Position Control, it is essentially the Torque Control frequency compensation that is what I need advice on.
Regards,
Wade

Wade,
for this purpose you will have to change the feedback for your motor to a signal that is proportional to torque. One option is to use a torque sensor with an analog output signal in the range of +/- 5 V or +/- 10 V. You can use an NI-Motion control device in analog feedback mode then and instead of defining a position profile you could define a torque profile then (e. g. by using contouring mode). With such a setup the motor will travel as far as it is needed to generate the torque profile, regardless of the travel distance.
To learn more about analog feedback, please have a look at this thread.
Regards,
Jochen

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Torque control is not working for my system using analog feedback

In the test bed, we are testing a brushless DC motor and a load motor generates torque to the test motor. The test motor is running with torque control scheme. They were connected together and I measured the torque signal to feedback the signal and control it. However, I just realized it only control when the torque was static. If I commanded a certain torque value (in this case, counts command), it kept generating that value. However, it did not generate the same torque in different position. I heard NI motion controller could develop torque values by mapping the torque signal with encoder signal. If it's true, the torque generation based on analog feedback, also, needs constraint by rotor position, right? W
hen I turned on the load machine with constant speed (50 RPM), the torque from the test motor did not provide the constant torque that I commanded. It generated the fluctuated torque values. This means the max torque was generated at one point and decreasing by rotating the shaft and increasing the torque. Keep going in this way. Could you please tell me if this is the correct response when we are using analog torque feedback?
Thank you.

Try the following:
1.-Set your test motor to encoder feedback instead of analog feedback.
2.-Load a velocity move on the axis for the test motor.
3.-Set the following error limit on you axis to 0 (disable following error).
4.-Use the load torque limit function to limit the amount of torque the 73xx PID loop will generate,this value is in volts, so you will need to do a correlation between the voltage output from the controller and the torque reported by your torque cell.
5.- Start the load motor.
6.-Engage the cluch.
7.-Start the velocity move on the test motor, you will see the torque ramp up to the torque limit.
8.-Call the load torque limit function on the fly to vary the torque setpoint to where you want it.

Is it possible to do torque control using Flex Motion?

I am trying to control the output torque to a motor?
I know you can do velocity control using FlexMotion, how about torque control?

To hold a servo motor at constant torque, all you need to do is provide a constant voltage. You can accomplish this using the analog output (DAC) of a FlexMotion board. To gain access to the DAC, configure the axis as an open loop stepper, then use the Load DAC.flx VI to output an analog voltage. The downside to this is that you won't have feedback, so you'll have no way to determine your position.

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Why does the Ni-Motion Torque-Control Program give me such an oscillation???

Hello,
I really hope to find somee help here...I have a UMI-7744 and I would like to do force control for a servo motor. I have tried the NI-Motion example "Torque Cntrl Using Monitoring Force"...it seems to be quite easy - it constantly measures the current force and compares the ADC-values with the target force. The difference between the two is then new relativ position...
When I test it with an actuator that does not touch the workpiece (current force==>0N) and then tell it to apply 50N (ADC-value of ~1000) then of course it starts moving towards the workpiece, but then overshoots quite significantly when it touches it, then undershoots, then overshoots, then undershoots....etc....
(1) Apart from the big overshoot, I would have assumed that the failure decreases over time and the force will be maintained at some point, but the actuator keeps on oscilating around the target force with quite high amplitudes.......does any body have an idea for the reason?????....How is it possible that the controller actually approaches the target force, ie. the over/undershoot should get smaller with every cycle...
(2) I was assuming that the problem is because I load quite large relative positions (1000 - 0 = 1000) while the actuator is not yet in contact with the workpiece which then causes the overshoot when the actuator touches the workpiece. Hence, I tried limiting the relative positions to +/- 100, but it seems that it does not improve anything. The actuator still never maintains a steady force.Any idea, why limiting the relative positions does not have an effect on the oscillation??
(3) I have seen that the use a delay of 50ms. Hence every 50ms a new target position is loaded. Is there any experience of what the BEST time delay is for motion control???? Is it better to decrease the delay to adjust the relative position more often OR would this have negative effects because the moves don;t have enough time to complete??????
I am grateful for any reply...

Hi Jochen,
thanks for the clarification on the pros and cons of the two Torque control approaches...very enlightening......
To clarify my previous question: I am using the S200VTS-Servo Drive from Danaher Motion. The drive is able to run in Torque-mode, Velocity-mode and Position-mode. In the latter case it needs a "step and direction" input, instead of an analog input. My idea was to setup the S200-drive in Position-mode because in the "Torque Control using monitoring Force"-example the inner PID loop is for the position...so I thought, why shall I setup the S200-drive in torque mode, when actually the PID-loop tries to control the Position.....you know what I mean? It appeared to me, that with setting up the drive in torque mode and running the example code with the positional PID-loop I am mixing force and position....
Kind regards and thanks a lot for your efforts.
Well, let's take it like that: The second approach is ok, if the dynamics of the torque are very low. The worst case scenario for this approach is a solid actuator pressing against a solid workpiece. When these two pieces meet, a force occurrs almost instantaneously. That means, that very short move distances result in high force differences. With your current approach this means that it's very hard to control the force, as in fact the only way to generate force is to move the axis a bit. If you control the force directly instead (analog feedback), you will get a much better control behavior.
To clarify the idea behind that:
Just think of two metal plates lying on each other on the floor. Now you step on the upper metal plate. Does the upper metal plate move? No. Is there a change of the force applied to the lower plate? Yes.
To summarize: 'Torque Control using monitoring force' works best in systems with very low dynamics and a soft contact between actuator and workpiece. still all the limitations that I have mentioned in my first post are true, so I strongly recommend to use analog force feedback.
Your last statement about running the motor in position or torque mode is not clear to me. Are you referring to operation modes of your drive (by the way, which drive are you using?). In this case the clear recommendation is to configure your drive always in torque mode, regardless of the type of control provided by the 73xx device that you are using. From a drive's point of view 'torque mode' means, that the analog input voltage (command input) is converted into a proportional current signal and that's in both modes the best option.
Jochen

Different temperatures (?)

I take the different temperatures using varied software and the values agree single in some.
What´s happening? Who lies?. ??? ???
My system is: E4300 @2700 Mhz + MSI P6N SLI-Fi + OCZ DDR2 800 Mhz
Core Temp
MSI PC ALERT
EVEREST Ultimate Edition 2007 - 3.80.948
TAT (INTEL Thermal Analisis Tool)
Thanxs in advance.
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Don't believe in any those programs except CoreTemp
As I already explained (not sure if in this forum)
E4300 it's the first Intel processor to implement a DTS internal sensor (inside CPU not external) = Digital Thermal Sensor.
Also, because intel wants to standarize the format, they had taken out the external DTS sensor that is present on all the E6x00 family of processors in the E4300, so, basically, what you can read from the external DTS sensor in the E6x00 is no longer available in the E4300 hence, the majority of programs extrapolates the values and you have a mess of terrible proportions... this is intel's fault since they didn't specify this change openly and you have to figure it out for yourself.
If you read the specs for E6x00 you will see something like "Digital Thermal Sensor included" and you will not see this in the E4300.
The E4300 includes a DTS internal (that means INSIDE the core, not outside) this is part of the PECI specification, so, basically that means one thing.
Unless you have a program that can READ the INTERNAL DTS Sensor on the E4300 you will get stuck with UNREAL numbers.
Progrmas that FAKE the temp because they DO NOT read the internal DTS sensor on the E4300 correctly are:
old versions of Speedfan, TAT (specially this one, DO NOT believe in this program for E4300, average 15 degress out of scale) and all Motherboard apps like MSI, Asus Suite, etc.
The only ONLY program to my knoledge that can read the internal DTS sensor on the E4300 accurately is the CoreTemp, the rest is nightmare and chaos.
Since PECI has been implemented, once the motherboards starts to use PECI, the programs will start to show correct values, I will explain.
PECI checks for PECI capable processors, when PECI is enabled, all readings concerning CPU temp, be it, external, internal CPU external sensor or Internal DTS (real value) will be redirected to the internal DTS Sensor, so... basically, all programs will report the correct Internal DTS temp reading when PECI is enabled, this will hopefully fix all the discrepancies..
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PCI-7344 Servo Torque Control

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.

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

Torque control and the dac function

Hi,
I would like to send a +- 10 V signal to a Parker servo drive. the drive is setup for torque control with +10 = 2800mA.
I'm using Viusual C++ with the flexMotn library. How do I set up my application to to communicate my torque value in counts (+-32767) to the +- 10 Volt analogue signal required by the drive. I'm trying to acive this using the following commands:
err = flex_set_op_mode (boardID, axis, NIMC_ABSOLUTE_POSITION);
CheckError;
err = flex_load_torque_lim(boardID, axis,16383, -16383, 16383,-16383, 0xFF);
CheckError;
err = flex_load_dac(boardID, 0x31, 3280, 0xFF);
CheckError;
// Start the move
err = flex_start(boardID, axis, 0);
CheckError;
Sleep(2000);
The code compliles fine and excutes, but the motor doesnot move.
I have also tried to perform a position move and read the DAC values during the move this also failed.
err = flex_load_target_pos (boardID, axis, -10000, 0xFF);
err = flex_read_dac_rtn(boardID, 0x31, DACValue);
CheckError;
Does anybody have any ideas?
Thanx
Thivash

Hello Thivash,
Thank you for contacting National Instruments. One thing to check for is if the DAC channel that you are trying to control programmatically isn't already reserved for a servo axis. You can check for this in MAX by going to the axis number of the DAC channel that you wish to control, i.e. axis 1 for DAC channel 1, and check to see if it is set to servo as shown in the attached image. If it is, switch the type to Stepper, save the settings, and re-initialize the motion card. You should now be able to programmatically control the DAC channel.
Regards,
Mike T
National Instruments
Attachments:
axis DAC settings.JPG ‏17 KB

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Torque Control on componet at different temperatures

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