In the last topic, we introduced the six axis force sensors used in automobiles, machine tools and robots. Some people often ask us why these industries use six-axis force sensors instead of three-axis force sensors. Is it unnecessary to measure bending moments in three directions? Today we will explain this questions.
If the direction and action point of the force are fixed, you can choose to use a load cell force sensor for measurement. Through installation and positioning, we can make the direction and action point of the force consistent with the calibration coordinate axis of the force sensor, so that the force can be accurately measured. For example, in this figure (picture 10), the calibration coordinate axis of the one-dimensional force sensor is the OZ axis. If the direction of the measured force F can completely coincide with the OZ axis, then the measurement task can be completed with the Weighing Sensor force sensor.
If the direction of the force changes randomly, but the acting point of the force remains unchanged and coincides with the calibration reference point of the sensor, then we should use a three-axis force sensor. Because the measured force can be decomposed into three orthogonal components under the calibration coordinate system of the three-axis force sensor, the three measuring units of the three-axis force torque sensor can measure these three components separately. For example, in this figure (picture 11), the action point P of force F always coincides with the calibration reference point O of the sensor, and the direction of force F changes randomly in three-axis space. In this case, three-axis force sensing can complete the measurement task, and it can simultaneously measure the force of Fx, Fy, and Fz.
If the direction and action point of the force change randomly in the three-dimensional space, the six-axis force sensor should be selected for measurement. Because the force at any action point in space can be decomposed into three components along the calibration coordinate axis and three moments around the calibration coordinate axis in the calibration coordinate system of the six-axis force sensor. For example, in this figure (picture 12), the force F in any direction in space, its action point P does not coincide with the sensor calibration reference point and changes randomly. In this case, it is necessary to select a six-axis force sensor to complete the measurement task, and simultaneously measure the six components Fx, Fy, Fz, Mx, My, Mz.
As mentioned earlier, customers often ask “if I only want to know the force in three directions, can I only use three-axis force sensor”. Our suggestions are as follows:
If the point of application of the force is close to the calibration reference point of the sensor and does not change. Customers do not have high requirements for the accuracy of measured data, and three-axis force sensors can be used.
If the acting point of the force is far from the calibration reference point of the sensor and changes randomly. Customers have high requirements for the accuracy of measurement data, so Hex Force/Torque Sensor must be needed.
The internal algorithm of the six-axis force sensor will decouple the interference between forces and moments in all directions, making the force measurement more accurate. Therefore, when the customer needs accurate measurement, we recommend using the six-axis force sensor. Not only can we accurately measure the force, but also we can use the moment information to calculate the attitude of the stressed parts after obtaining the moment information; At the same time, it can also monitor whether the torque is within the safe range to avoid overload damage of the sensor.
In the last picture, the six-axis force sensor is used on the end joint of the robot (Figure 13). It can be seen that the sensor is also connected to an actuator, such as a grinding head or a clamping jaw. So the arm of force during the operation of the actuator is between tens of to two or three hundred mm. The arm of force is relatively large and also changes randomly. So the force sensor on the robot generally adopts the six-axis force sensor.