Force Balance Sensor Based On Electromagnetic Force Balance Lever Structure

Force sensor is a very important part in force measurement field, which is the foundation of mass properties(quality, centroid, rotational inertia and moment of inertia). The elastically sensitive element nonlinearity and the signal–noise ratio are the limitation of the traditional force transducer, which makes the precision is rarely higher than 0.02%. This paper proposes a force transducer with electromagnetic force balance lever structure, which improves the nonlinearity and solves the signal-noise ratio problem to acquire high precision.Firstly, the principle and the implementation mechanism of the sensor were proposed by analyzing the operating principle of normal force balance sensor. Then the mechanical structure of the sensor was designed, including single-point sensor and three-point sensor.Secondly, the electromagnet were designed and analyzed, which was used to produce the electromagnetic force. The electromagnet structure parameters were designed including the structural form and the design of the coil. Finite Element Method analysis was performed on the electromagnet, and the relationship between coil voltage and electromagnetic force was obtained, which verified the nonlinearity of the curve.Thirdly, the characteristics of electromagnet were analyzed. The gap and temperature were the main reasons of the nonlinearity. To solve this problem, the electromagnetic force curves under different temperatures were fitted by the piecewise linearization method, which acquired the high linearity electromagnetic force.Then, the hardware circuit for the electromagnetic force control system was designed. The electromagnetic force was controlled by the method of DC chopping circuit. Through the signal collection circuit and monitoring the sensor by pressure sensor, temperature sensor and hall current sensor, PWM was generated by the EV module of TMS320F2812 in order to control the DC chopping circuit. The software was also designed, which was based on hardware circuit. The software included the signal collection module and the PWM module.Finally, the experiment table of the sensor was built. In order to test the performance of the sensor, the experiment of repeatability, the experiment of position error and the experiment of temperature were done and the causes of errors were analyzed.