Frequently Asked Questions
Ready to add force-sensing to your robotic system, but still have questions? Check out our most frequently asked questions to learn more, or ask an engineer.
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A force torque sensor is an electronic device that converts the physical quantity of force and torque to a signal that can then be read by a human and/or a robot.
An object can experience force and/or torque from various sources. In continuum mechanics, bodies are considered deformable. When a force is applied, deformation takes place. Deformation is directly related to the force applied. One way to measure deformation is by attaching a film of variable electrical resistance to the deformed body surface by glue or other methods to share the same deformation. The resistance changes when the body elongates or compresses, due to force applied. This change is then captured by an Analog to Digital Converter (ADC) and is recorded as a digital counter. Then, it is processed by a microcontroller and sent via the communication channel of the system's network for further processing.
A simplified example of processing:
When a force of 100 N is applied, the digital counter records a change of 1000 counts. The most simple sensor design is to have a linear relation between force and the change of counts. In this case the force is directly proportional to the change of counts by a factor of 10. If a change of 1500 is recorded then a force of 1500/10 = 150 N is applied. It is safe to say that if a change recorded is divided by 10 we can simply calculate the value of force applied. This is what happens on a digital weight scale. The only difference is that weight scales show the mass of an object by dividing force by the gravity acceleration of a specific location (usually the calibration location).
For a 6-axis force torque sensor, three force and three torque components of the force/torque vector are applied and six signals from six different variable resistances can be recorded. Each one of these components affects, to a greater or lesser degree, the individual variable resistances that are located at the different spots on the sensor body. By linear combination of the six signals through an individual calibration matrix, the physical quantities of force and torque are obtained.
Sensor selection is primarily dependent on the application. Each application is unique and requires a force torque sensor to have certain features, ranges, or software specifications.
Check out our blog post on how to select a force torque sensor for more details.
To get the best force torque sensing solution, we recommend contacting us and sharing your application details.
Unbox the sensor carefully and read the Quick Start Guide and User Manual l before using your FT sensor.
We recommend navigating our FAQ, like you're currently doing, to understand how our sensors work and resolve common concerns about using FT sensors.
Bota Systems sensors come pre-calibrated with a calibration matrix saved on the device.
The only calibration required is an offset calibration that can be done externally by gathering data while the sensor is steady and no change in the dynamic state is happening. After the data is averaged, it can be subtracted from the current measurements.
Sensor sensitivity is directly related to the sampling frequency. The internal sensor filters can be utilized to increase the sensitivity.
The user manual provides a table with all available filtering options and the resulting resolution after a filter is applied.
Note: The internal filters are hardware filters optimized for a force-torque sensor signal. One can potentially run the sensor at full speed and apply one's own filtering.
It depends on the maximum force being applied and the resolution requirements of the application.
The Rokubi sensor has 0.2N noise-free resolution on the z-axis at 1000Hz and a range of 1200N. For example, if the maximum force to be applied on the z-axis for your application is 300 N and the resolution required is more than 0.2N, then Rokubi is a sensor that can be used for your application.
We define noise-free resolution as the 6 sigma (σ) of a signal. σ stands for the standard deviation of the signal. It is calculated by recording 10 sec of measurements when the sensor is in a static condition. 6σ defines the peak-to-peak range that the noise level will remain below for 99.73% of the time.
Did you know, in most robotic systems, noise is inevitable? However, noise corruption is unacceptable for applications, especially those that are safety-critical, like robotic-assisted surgery. Learn more about reducing signal noise.
