What is torque ripple? How does it affect the operation of the motor? If so, what is the impact? What does it mean for our production and life? How do we test torque ripple? Let's take a closer look at the torque ripple.
First, what is the torque fluctuation
Torque fluctuation is the torque fluctuation of various working machinery transmission shafts. It is closely related to the working capacity, energy consumption, efficiency, operating life and safety performance of the power machinery. The measurement of the torque determines the load of the transmission shaft. Control, the strength design of the working parts of the transmission system and the choice of the prime mover capacity are all important. In layman's terms, the motor fluctuates up and down due to the mechanical structure and its own rotor inertia output.
Torque fluctuation is mainly affected by factors such as cogging torque, electromagnetic fluctuation torque, armature reaction and mechanical process. It is precisely because these factors are caused by the mechanical structure of the motor itself, which is especially difficult to test. And the accuracy is not high.
Figure 1 Torque fluctuation trend
Second, the impact of torque fluctuations
The motor acts directly on the load. During operation, its own torque fluctuation due to cogging torque, electromagnetic effect and machining assembly process will be directly transmitted to the load, which will affect the system speed stability and control accuracy. Especially in the light load and low speed state, the wave torque accounts for a relatively large proportion of the motor output torque, and this effect can not be ignored. Therefore, accurate measurement of the fluctuating torque becomes a problem that needs to be solved in the practical application of the motor.
Figure 2 Torque fluctuation test
Third, the torque fluctuation test method
According to the test basis of the national standard "GB/T30549-2014 AC servo motor general technical conditions", the following test methods are available:
Blocking method
Using the magnetic powder brake as the load, when measuring the rated current of the motor, the rotor is divided into the stall torque at 10 points in the range of 360/(2p) (p is the number of poles of the motor), and the maximum value of the stall torque is found respectively. And the minimum value, you can use the formula to calculate the torque fluctuation.
Direct test
The magnetic powder brake is used as the load, and the load motor is used to make the motor under test work in the maximum torque specified in the continuous working area. The motor is controlled to run at the minimum speed. The torque sensor is used to record the torque of the motor during one week of operation, and the maximum rotation is recorded. Moment and minimum torque, the formula can be used to calculate the torque fluctuation coefficient. (Formula with blocking method)
Figure 3 test section
Due to the harsh test conditions of the torque ripple, the current test method is mainly based on the stall method. The reason is that other methods lead to large errors in the test process and cannot be accurately tested. Figure 3 shows the test part of the stall test. The torque sensor is connected between the motor and the load. Research at home and abroad mainly focuses on the development of the torque sensor. The development of the new torque sensor is of great significance for the improvement of the stall measurement method. At present, the development of high precision, fast response, non-contact torque sensor has become a hot research direction.
Fourth, the principle of torque fluctuation generation
Ideal cogging torque fluctuation
The structure of a general permanent magnet torque motor is a structure in which a rotor is assembled with a permanent magnet and a stator is slotted. The cogging torque is a fluctuating torque with a mean value of zero generated by the interaction of the permanent magnet and the edge of the stator tooth, which is generated by the change of the magnetic field energy of the rotor of the motor during operation.
Figure 4 Ideal cogging torque fluctuations
Torque fluctuation caused by armature reaction
It is assumed that the magnetic field distribution is not affected by the armature reaction, but the motor always produces an armature reaction during operation. The cross-armature armature reaction will cause the magnetic field to be distorted, causing the asymmetry of the entire magnetic field distribution, thereby changing the back-EMF waveform. Torque fluctuations are generated. For a permanent magnet torque motor, the change in the magnetic field distribution of the armature reaction is negligible due to the close proximity of the magnetic permeability of the permanent magnet material used and air.
Fifth, the test principle
The motor torque ripple acts on the drive shaft to generate stress, which causes the deformation of the drive shaft. The torque sensor measures the torque at the input end indirectly by measuring the deformation of the drive shaft. The torque sensor is the core part of the dynamic measurement system for torque fluctuations. At present, there are many types of torque sensors, but the resistance strain gauge torque sensor is still the mainstream choice because of its fast response, high linearity and high measurement accuracy.
Guangzhou Zhiyuan Electronics Co., Ltd. can accurately and effectively test the torque ripple of the motor by configuring a high-precision torque sensor (accuracy up to 0.1%). At the same time, a reasonable loading method is adopted to ensure that no other inertia is introduced during the test. As a senior company in the industry, with many years of industry experience, to ensure the authority of testing.
Summary
In summary, we understand that torque ripple is closely related to the working capacity of the motor, energy consumption, efficiency, operating life and safety performance, and plays a vital role in our production and life. Nowadays, through advanced direct measurement, torque fluctuations can be accurately tested to ensure high-precision testing.
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