I. Physical characteristics of the sensor itself
Strain gauge performance
Strain gauges are one of the core components of a six-dimensional force sensor, and their accuracy directly affects the sensor's measurement accuracy. The sensitivity coefficient of the strain gauge determines its sensitivity to stress changes. If the sensitivity coefficient is inaccurate or changes during use, it will lead to deviations in the measured force and torque values.
For example, the quality of strain gauge materials varies. Low-quality strain gauges may produce different strains under the same stress due to material inhomogeneity, thus affecting measurement accuracy. Moreover, strain gauges may experience fatigue after prolonged use, leading to decreased sensitivity and consequently reducing sensor accuracy.
Properties of elastomers
An elastomer is a component that bears external forces and transmits those forces to strain gauges. The stability of the elastic modulus of an elastomer is crucial to the accuracy of the sensor. If the elastic modulus changes with factors such as temperature and time, the amount of deformation of the elastomer under the same external force will change, thus affecting the output signal of the strain gauge and ultimately leading to a decrease in measurement accuracy.
For example, the elastic modulus of some elastomer materials decreases at high temperatures, affecting the measurement accuracy of sensors operating in high-temperature environments. Furthermore, the manufacturing precision of the elastomer also impacts sensor accuracy. If the elastomer's dimensional accuracy is low, its stress distribution under load will be uneven, preventing strain gauges from accurately sensing the magnitude of the force.
II. Installation Factors
Installation location and orientation
The accuracy of a six-dimensional force sensor is significantly affected by its installation position and orientation. If the installation position is incorrect, such as not installing it at the specified position and angle on a robot arm, the force and torque measured by the sensor will not be the accurate values in the actual direction to be measured.
For example, when installing sensors on the end effector of a robotic arm, if the coordinate system of the sensor is not precisely aligned with the operating coordinate system of the robotic arm, the force and torque measured by the sensor will include additional components due to the installation deviation when the robotic arm operates, resulting in measurement errors.
Installation firmness
Loose installation can introduce additional interference and vibration, thus affecting the accuracy of the sensor. If the sensor becomes loose during operation, it will generate additional shaking and displacement when the robot moves or is subjected to external forces, causing the strain gauge to sense inaccurate force and torque signals.
For example, in industrial environments, there are frequent sources of vibration, such as the operation of large motors or compressors. If the sensor mounting bolts are loose, these vibrations may be mistaken by the sensor as external force signals, leading to fluctuations and errors in the measurement results.
III. Work Environment Factors
Temperature change
Temperature is a crucial factor affecting the accuracy of six-dimensional force sensors. Temperature changes cause thermal expansion or contraction of the sensor's internal components. For strain gauges and elastomers, temperature variations alter their physical properties.
For example, increased temperature can cause changes in the resistance of a strain gauge, generating a thermal output signal that interferes with normal force and torque measurement signals. Simultaneously, temperature changes can also affect the elastic modulus of the elastic body, as mentioned earlier, thus impacting the sensor's accuracy. Some high-precision sensors are equipped with temperature compensation circuits to minimize the impact of temperature on accuracy, but the compensation effect has its limitations.
Humidity and corrosive media
High humidity environments can cause moisture to seep into the internal circuitry of sensors, affecting the performance of electronic components. If a sensor is exposed to a humid environment for an extended period, moisture may penetrate the internal connections, causing short circuits or corrosion, thereby reducing the sensor's accuracy.
In environments containing corrosive media, such as chemical production workshops, the sensor's housing and internal components may be subject to chemical corrosion. For example, acidic or alkaline gases may corrode strain gauges and circuit components, altering their performance, gradually reducing the sensor's accuracy, or even causing sensor damage.
Electromagnetic interference
Industrial environments contain numerous electromagnetic devices, such as motors and welding machines. The electromagnetic interference generated by these devices can affect the accuracy of six-dimensional force sensors. Electromagnetic interference may induce currents in the sensor's signal transmission lines, interfering with the normal output signal of the strain gauges.
For example, if a six-dimensional force sensor used near an electric welding operation does not have proper electromagnetic shielding, the high-frequency electromagnetic signals generated by the welding will cause the sensor to output incorrect force and torque signals, resulting in a serious decrease in measurement accuracy.
IV. Signal Processing and Calibration
Signal amplification and filtering
The raw signal output by a six-dimensional force sensor is usually very weak and needs to be amplified. If the gain of the signal amplification circuit is inaccurate or there is drift, it will cause a deviation in the proportional relationship between the amplified signal and the actual force and torque signal, thus affecting the accuracy.
At the same time, signal filtering is also very important. If the filtering parameters are set improperly, such as an inappropriate selection of the filter cutoff frequency, some effective signals may be filtered out or noise signals may not be effectively filtered out, resulting in errors in the final measurement results.
Calibration accuracy and frequency
Sensor calibration is a crucial step in ensuring accuracy. If the calibration equipment itself is not accurate, the accuracy of the calibrated sensor will also be affected. Moreover, sensor performance can change over time and with variations in the working environment, necessitating periodic calibration.
If the calibration frequency is too low, the accuracy degradation that occurs during sensor use will not be detected and corrected in a timely manner. For example, in high-precision measurement applications, monthly or even weekly calibration may be necessary to ensure that the sensor's accuracy meets requirements.
