Robot Force/Torque Feedback Control, Hypersen 6-Axis Force Torque Sensors Are Applied in Multiple Scenarios

In the 1970s, Chinese robotics technology process began to take off. The application of robots in various industries has become more and more widespread. From simply replacing low-precision repetitive labor to obtaining sensory functions through high-precision sensors, robots will go towards artificial intelligence in the future.

Robot technology and application development can be divided into three stages and four levels. The key factors for the development of the three stages are, demographic dividend, engineer dividend, and artificial intelligence technology advantages. By virtue of its demographic dividend, China has quickly passed the automation stage. There are already many leading industrial robot companies in our country. At present, we are in the transition stage from machine intelligence to artificial intelligence like leading countries in robotics fields, such as Japan and South Korea. Regarding the accumulation of artificial intelligence technology, we are also in the forefront of the world.

6-Axis Force Perception Broadens Application Boundaries

Currently, traditional position control is almost used in every industry, such as allowing the robotic arm to move in a closed and confirmed space along a pre-planned trajectory. Or the position-controlled robot has a certain ability to adapt to the external variable environment with the feedback of the vision system (Vision System). The advancement from automation to machine intelligence and artificial intelligence requires the assistance of high-precision sensors. The sensitive vision system acts as the eyes of robots. In addition to helping the robot work better, it can also guarantee safety in work. However, as the application boundary of robots continues to widen, visual empowerment alone cannot meet complex practical applications. At this time, it is necessary to introduce force/torque output control, or to take force/torque as closed-loop feedbacks. Since the contact surface between the robotic arm and the working surface is often unknown, curved and complex, the perception of this force/torque must be multidimensional. The six-dimension force torque sensor we are talking about refers to a sensor that measures the force and torque in three space directions of X, Y, and Z.

The 6-Axis Force Torque Sensor is a newly developed force sensor that can simultaneously convert multidimensional force/torque signals into electrical signals, which can be used to monitor and measure force and torque that change in direction and magnitude. Besides, acceleration, inertial force and the magnitude and point of contact force can also be detected.

The 6D force torque sensor can give the robot the perception of force and torque changes, and perform more complex tasks on the basis of simple mechanical repetitive motions, such as precision assembly, force controlled flexible pick & place, polishing, insertion & assembly, etc. The performance directly depends on the robot's perception of force，the controlling accuracy and speed. So, why do we need to pay attention to force control? Why is force control so important? There is a consensus that force control must be introduced into the field of robot motion control in the future. Position control alone is not promising.

As a technology company focusing on the research and development of high-end intelligent sensors, Hypersen has independently developed and produced chromatic confocal displacement sensors, high-speed industrial cameras, six-dimension force torque sensors, laser cross beam sensor and other premium smart sensors based on years of experience in industrial mechanics and optics. The above products have obtained a number of national patents and passed international certifications such as CE, FCC, RoHS, IEC62471, IEC60825 and so on. Among the products, the HPS-FT series six-dimension force torque sensor, as a classic product of Hypersen, provides a superior robot force control solution, and gives higher performance and operability in the six-dimension force control.

The main indicators to measure the performance of 6-Axis force torque sensors include measuring range, accuracy, anti-overload capacity, data output frequency, non-linearity, creep, hysteresis, zero drift, temperature drift and crosstalk. Besides, there are also influencing factors like decoupling algorithms, filtering Algorithms, temperature compensation algorithms, etc. As a sensor that gives the machine a sense of touch, it can be used in a wide range of applications in robots and mechatronics equipment. There are many factors that can affect customer experience, such as the accuracy of force control, measuring range, and anti-interference ability in various environments. To satisfy customers’ needs, suppliers should meet high requirements on the R&D both in software and hardware.

In terms of hardware, Hypersen’s self-developed HPS-FT series of 6-Axis force torque sensor adopts a high-precision strain gauge and compact structure to achieve higher signal-to-noise ratio and sensitivity. Thanks to its IP67 dustproof and waterproof level, it can collect data accurately even in many hash environments. Regarding the software, the built-in temperature compensation algorithm greatly reduces the temperature drift caused by temperature changes. What’s more, the high-precision decoupling and filtering algorithms help this sensor perform better with a low level of zero drift, temperature drift, and crosstalk.

Applications of 6-Axis Force Control in Multiple Scenarios

As the applications of robots become more and more extensive in industries and human lives, a consensus has been reached. That is, force control must be introduced into the future robot motion control because position control alone is not promising. In the future, the requirement for robots is to enter human lives, which not only requires robots to interact with human beings safely in physics, but also requires flexible impedance control, the ability to move in unknown environment, the ability of fast dynamic control and adjustment. All of the above requirements are inseparable from force / torque control.

Force control sensors are generally installed in the "limbs" of the robot. The 6-Axis force torque sensor is connected with the end joint of the robot arm through a flange. Then, it measures the force & torque data in X, Y and Z directions and transmits them to the robot through a cable to realize force control in 6 dimensions. The output frequency of Hypersen’s 6D Force Torque Sensor can reach up to 2000Hz, which enables the robot to sense and control the force and torque in real time. In addition, it also enjoys a high accuracy of 0.05N (Fxy, FZ direction) and 0.001nm (Mxy, Mz direction). This sensor can be applied in force control polishing, precision assembly of small workpieces, flexible picking of soft package, USB flexible plug-in, bolting and other works.

In addition to the force & torque control, the IO of Hypersen’s EtherCAT/Ethernet adapter can be connected to the emergency stop IO of the robot and can set the alarm threshold. When the threshold is exceeded, the adapter issues an emergency stop command to the robot through the IO signal to make it pause. The ultra-sensitive pressure transmission system of the sensor has a fine anti-collision emergency stop function, which can protect the user's personal safety and prevent equipment damage effectively.

Robots equipped with 6D force torque sensors can also control the end contact force of the robot accurately based on fuzzy adaptive admittance control. Repetitive tasks through hand guiding and path & force recording is the most commonly scheduled tasks for robots. In the medical rehabilitation industry, more and more tasks such as cervical spine orthopedic traction and rehabilitation are being handed over to robots.

In order to adapt to the work requirements in different scenarios, Hypersen has developed a variety of different models of 6D force torque sensors. HPS-FT120 has a maximum measuring range of 5000N, 150Nm, while HPS-FT025 has a minimum range of 150N, 4Nm, which covers the load range of most applications with a static overload capacity up to 500%. In addition, the stainless steel HPS-FT060S has stronger rigidity and can adapt to higher-intensity work and more complex working environments.

Humans identify the shape and position of objects through various senses. In the future, robots may also be able to accurately confirm the position, shape and state of objects by the ability of seeing, hearing, touching, and smelling. Adhering to the company philosophy of “Winning the market with technology, treating customers with honesty”, Hypersen is committed to the establishment of first-class, high-end intelligent sensor brand, so as to promote the transformation of domestic sensor technology from "Made in China" to "Made in China Intelligently" and help industrial robots become more intelligent and flexible, assisting robots to move towards "the merging of humans and machines".