Force Torque sensors are mainly used in industries requiring torque measurement and control. Accurate torque measurement is crucial for maintaining equipment safety and ensuring production processes.
Generally speaking, the most important application of torque sensors today is in the robotics industry. Torque sensors are installed on various joints of robots to control the magnitude and accuracy of joint movement. This post will focus on torque sensors and their application to robotic torque measurement.
What is a Force Torque Sensor?
A force torque sensor, also known as a torque transducer, is an instrument used to measure the torque applied to an object. It converts the measured torque into an electrical signal. The electrical signal is then processed and displayed by a computer. A Force Torque Sensor can be categorized as a static or dynamic torque sensor. Static torque sensors measure torque during discontinuous rotation (<360°). While dynamic torque sensors measure torque during continuous rotation (>360°). They can sense torsional forces on many rotating or non-rotating mechanical components, typically measured in N·m.
Advantages:
- Customization available;
- Good reliability;
- High accuracy;
- Long life;
- Fast frequency response.
Disadvantages:
- High cost;
- Highly susceptible to environmental influences;
- Nonlinear error;
- Complex installation.
Force Torque Sensor Operation Principle:
The Force Torque Sensor is based on the resistive strain gauge. The core of this principle lies in the bridge effect of strain gauges. In a torque sensor, a strain gauge is mounted on an elastic shaft. The strain gauge is a vital element for measuring torque.
When a torque is applied to the elastic shaft, its shape and size change, generating strain. The strain gauge senses this strain, causing a change in its electrical resistance. Usually, a strain gauge is made of a material with electrical resistance properties. When subjected to torque-induced strain, the gauge’s resistance increases or decreases according to a specific pattern. This resistance change is converted into a voltage or current signal via a bridge circuit. This signal represents the torque measurement.
In addition to traditional resistive strain gauge torque sensors, non-contact torque sensors are also a key area of technological development. Non-contact torque sensors include fiber optic torque sensors and magnetic torque sensors. Non-contact torque sensors utilize optical or magnetic principles to measure torque, avoiding the wear and contact resistance issues that may exist with traditional contact sensors.
Force Torque Sensor Application Industries
Based on our years of experience supplying torque sensors, we have concluded that torque sensors are primarily used in the following areas:
- Torque control of robot joints;
- Measurement of output torque and power of rotating power equipment such as motors, engines, and internal combustion engines;
- Also used for torque and power measurement of locomotives, automobiles, tractors, aircraft, ships, mining machinery, and other equipment;
- Used in the manufacture of viscometers;
- Used for measuring torque and power of equipment such as fans, pumps, gearboxes, and torque wrenches;
- Used for measuring the torque and power of sewage treatment systems;
- Used in laboratories, testing departments, and for production monitoring and quality control.
Sino-Inst Featured Torque Sensor
Analog vs. Digital Force Torque Sensors
Analog torque sensors and digital torque sensors represent two different output methods. The following is a detailed introduction.
Analog output is a continuously varying voltage or current signal whose magnitude is proportional to the applied force.
Digital output is a discrete digital signal. It is binary-coded and transmitted via a communication protocol. Digital signals contain information such as force magnitude, unit, and state.
characteristic | Analog output | Digital output |
Anti-interference ability | Weak, susceptible to electromagnetic interference | Strong, digital signal anti-interference ability |
Transmission distance | Short, significant signal attenuation | Long transmission distance can be extended through protocols |
Signal processing | Requires additional AD conversion | Can be directly processed by a microprocessor |
Accuracy | Limited by AD conversion | High, up to 24 bits or higher |
Cost | Low | High, involving complex circuits and protocols |
Flexibility | Low, limited functionality | High can integrate multiple functions |
All in all, analog output is suitable for short-distance, low-cost, and low-precision applications. Digital output, on the other hand, is suitable for long-distance, high-precision, and complex signal processing applications, such as robotics, medical equipment, and aerospace. Generally speaking, digital output requires careful consideration of compatibility with secondary instruments. Good compatibility ensures accurate measurement. If you’re unsure about which signal output to choose, I recommend consulting a professional technician or relevant supplier. Sino-Inst can provide you with free measurement solutions.
Why Force Torque Sensors Matter in Robotics
Managing the physical contact between the robot and the environment is crucial in robotic manipulation tasks. Due to the complexity and uncertainty of robotic systems, pure motion control is often insufficient. Even the most accurate models cannot fully predict all possible scenarios.
When a robot interacts with its environment, contact force is necessary. Excessive contact force can damage the object in contact. Insufficient contact force can hinder the robot from completing its task. So, precise control of contact force is important for the smooth functioning of a robot.
The invention of torque sensors is to solve the problem of the contact force between robots and the environment. Torque sensors can control the amplitude and accuracy of robot movement. By feedback the force, the robot can sense the contact force between itself and the object in real time and adjust its motion. Torque sensors can proactively adjust the robot’s interaction with the environment to ensure that contact force remains within an acceptable range.
The Function of Torque Sensors for Robots
Torque sensors are installed on the joints or end-effectors of a robotic arm end effector.
Main functions include:
Torque sensors measure the torque, thrust, and torque acting on the robotic arm’s end effector in real time, providing precise feedback. They are right for performing complex force control tasks, such as precision grasping, assembly, and loading, preventing operational errors or damage caused by excessive torque.
By monitoring abnormal torque and force, torque sensors can accurately identify collisions or contact between a robotic arm and an object. By sensing the magnitude of the force, the robot can take appropriate protective measures. For an application requiring high-precision motion control, such as precision assembly and welding, the right feedback provided by torque sensors helps robotic arms accurately control position and force.
Read More about: Robot Torque Sensor Guide
Force/Torque Sensors and Their Implementation in Robotics
In the field of humanoid robotics, force/torque sensors have become standard equipment for high-performance humanoid robots. They are typically installed at the wrist, ankle, sole, or hand. They play a key role in motion planning, posture adjustment and force sensing. Force torque sensor improves the dexterity of hand manipulation and the stability of foot walking, and enhances the autonomy and adaptability of humanoid robots in various environments.
Here are some important applications and installation locations for force/torque sensors in humanoid robots:
- Torque sensors installed at the wrist help robots perform delicate hand manipulation tasks such as grasping, carrying, and assembly.
- Torque sensors installed at the ankle or sole help robots sense ground reaction forces during walking and balance control, allowing the robot’s control system to adjust the posture of the humanoid robot’s arm and body, improving walking stability.
- Torque sensors installed at the contact points of the robot’s hand can improve the dexterity and adaptability of hand manipulation, especially in scenarios requiring compliant control.
- Torque sensors provide information about the torque that is crucial for robotic motion planning. They help robots better plan their movements.
Force torque sensors help robots maintain balance and stability during posture adjustments. They make robots to sense the forces interacting with external objects. This is useful for applications requiring precise force control.
How accurate is a force torque sensor?
Torque sensors are classified into accuracy levels of 0.1, 0.2, 0.5, 1, and 2. Grade 0.1 is the highest accuracy, with an error range of less than 0.1%. Grade 2 offers the lowest accuracy, with an error range of less than 2%. Different accuracy levels are suitable for various measurement scenarios. And users can select the appropriate accuracy based on their different needs.
How does a reaction torque sensor work?
Strain gauge torque sensors are the most common type. They utilize a semiconductor device—a resistance strain gauge—attached to an elastic shaft to sense the tiny deformations of the shaft caused by torque. This deformation causes the strain gauge's resistance to change, which is then converted into an electrical signal through a bridge circuit.
How do I calibrate a torque sensor?
Torque calibration can be performed statically or dynamically.
The progress for static calibration is as follows:
First, we need to prepare a standard torque source, a high-precision measuring instrument (such as an electronic scale or high-precision resistor), and a calibration fixture. It is necessary to ensure that all equipment is calibrated and in good condition.
We install the torque sensor on the calibration fixture, which ensures it is securely mounted. The axis of the torque sensor is aligned with the axis of the standard torque source.
Always warm up the sensor according to the sensor manual until it reaches a stable state. If any problems arise, consult a qualified technician.
Under no-torque conditions, the sensor output is adjusted to zero or a preset reference value.
Using a standard torque source, we slowly apply torque to the sensor at predetermined values. After each torque application, we should wait for the torque sensor to output a stable torque value and record the data.
The recorded torque value is compared with the reference torque value. Then, we create an error curve. Based on the error curve, we adjust the torque sensor's parameters (such as zero point, sensitivity, and linearity) until the required error accuracy is achieved.
If the measurement result is still wrong, we must repeat the above steps. This repetition is necessary for the stability and reliability of the calibration results.
If you meet any problems during the calibration process, please feel free to contact our engineers and technicians. Sino-Inst has been providing torque supply for over 20 years. We have professional engineers who can help you solve any problems you may have.
Here are dynamic calibration considerations:
Dynamic calibration is more complex than static calibration. We need to consider multiple factors, such as the sensor's dynamic response characteristics, vibration interference, and temperature changes. During dynamic calibration, it is often important to simulate actual operating conditions, such as speed and load variations. Dynamic calibration typically requires a dedicated laboratory or a site equipped with the necessary equipment and technical support.
All in all, force torque sensors are a key element for torque measurement in robots. After reading this post, you will have a general understanding of torque measurement and control in robots. If you also require a torque sensor for robot torque control, please feel free to contact us.
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