Torque Limiting vs Torque Control

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Joined: Thu Jan 11, 2018 11:44 am

Torque Limiting vs Torque Control

Postby om_tech_support_PB » Thu Feb 15, 2018 2:48 pm

This forum will cover the differences between torque limiting and torque control, which products offer these features, and examples of when to use each feature.

Many of our products come with either a torque limiting or torque control feature. Torque limiting is used to limit the maximum amount of torque a product can produce. Torque control sets how much torque the product produces.

The following products include the torque limiting feature: BX, BX2, BLE, BLE2, AR (labeled as push motion), AZ (labeled as push motion) and BLV. The accuracy of the torque limiting feature for brushless products (BX and BLE) is +/-20%. For the BX2 and BLE2, it was improved to +/-10%. The AR and AZ series both have an accuracy of +/-10% for their push motion operation. It is not recommended to use push motion with geared motors. For Torque Control, our NX series offers a torque control accuracy at 5.6%. Each product has its own way of setting the torque limiting or torque control value. Some can be changed via analog settings, digital settings, using the OPX device, or through MEXE02 software, so see each individual product manual for specific settings.

Setting a value for torque limiting is done by choosing a percentage of the motor’s rated torque as the maximum operating torque for the motor. (Note that 100% is used as the rated torque value.) For example, if a motor offers a rated torque value of 30 lb-in, and the torque limiting value is set to 50%, then the upper torque limit would be 15 lb-in. As you can see in the image below, torque limiting can be set as high as 250% for the BX2- others may vary. However, it is not recommended to operate any motor above its rated torque value for an extended period of time- usually 5 seconds. For more information on brushless motor torque specifications, please see the following forum:

BX2TorqueLimiting.png (111.23 KiB) Viewed 4019 times

The next image shows the settings for our AR series. You can see the torque limiting option is labeled as “push current” for push motion operations.

ARpushcurrent.png (123.48 KiB) Viewed 4019 times

A push motion-operation is used to pressurize a load continuously. For more information on push motion, see the following forum:

Now along with the Torque Limiting input, there is a TLC output on our products (also known as TLM in BX compatibility mode). The TLC output will signal when the motor has reached the torque limiting value. You can find more information about this output in each product's user manual.

With torque control mode in the NX series, the motor will operate at the set torque value. If an application, such as a rotary sanding application in which the motor rotates a workpiece into a rotating sanding belt, calls for a constant torque, a percentage of the motor’s rated torque can be chosen to operate at. This is done by controlling the motor’s current. The image below shows the MEXE02 software for our NX servo motor. The “Torque command”, or torque control percentage, is set to 50%. So for example, if this motor had a rated torque of 20 lb-in, then it is actually set to produce 10 lb-in.

NXtorquecontrol.png (65.23 KiB) Viewed 4019 times

For winding applications, the NX series can also operate in tension mode which can achieve a constant torque even with changing diameters.

Lastly, many factors can affect the accuracy of the actual torque output. To improve accuracy, a couple tips can be followed. First, keep the connection cable length as short as possible. Second, try to keep the load, speed and power supply conditions the same as that can increase accuracy and improve repeatability. If you have any further questions regarding these features, please contact tech support.

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