AC Tachogenerator is a micro special motor whose output electromotive force is proportional to the speed. The polarity of the output electromotive force changes when the direction of rotation is changed. When the tested mechanism is coaxially connected with the speed measuring generator, as long as the output electromotive force is detected, the speed of the measured mechanism can be obtained, so it is also called a speed sensor.
1. Simple structure, high reliability and large output slope;
2. Poor linearity, large phase error, and high residual voltage.
3.Simple structure, sturdy and durable, can distinguish the direction of rotation.
There are two types of AC speed measuring motors: asynchronous and synchronous speed measuring motors. AC tachometers are widely used in various speed or position control systems. As an element for detecting speed in an automatic control system to adjust the motor speed or improve system stability and accuracy through feedback
The output AC voltage frequency of the asynchronous speed measuring generator is the same as the excitation frequency, and its amplitude is proportional to the rotor speed. The structure of the asynchronous tachogenerator is the same as that of a common two-phase cage induction motor. Among the two-phase windings on the stator that are 90 ° apart from each other, one phase is an exciting winding, which is connected to an AC power supply of 50 Hz or 400 Hz, and the other phase is output. Speed signal. When the rotor stalls, the stator field winding only generates the transformer electromotive force in the rotor’s multi-symmetrical winding, so the rotor magnetomotive force and the stator magnetomotive force are in the opposite direction and play a demagnetizing role. The output windings perpendicular to these two magnetomotive forces No electromotive force is generated. When the rotor rotates, in addition to the transformer electromotive force in the cage winding, a cutting electromotive force will also be generated. The magnetomotive force generated by the cutting electromotive force is of a quadratic nature. It interlinks the output windings and generates therein a signal voltage proportional to the speed. The frequency of the signal voltage is the same as the power supply voltage. The phase difference between the signal voltage and the power supply voltage changes with the direction of rotation, so it is very suitable for use with AC servo motors.
In order to improve the accuracy of asynchronous speed-measuring generators, cup rotor asynchronous speed-measuring generators are widely used. The rotor of this motor is a thin-shell non-magnetic ring, which is made of silicon-manganese bronze or tin-zinc bronze with high resistivity. The inner and outer cups form a magnetic circuit with an inner stator and an outer stator, and the cup walls are not made of ferromagnetic material. . To reduce the air gap, the cup wall must be thin, about 0.2 to 0.3 mm.
The damped speed-measuring generator is an asynchronous speed-measuring device with a high theoretical value of stalled acceleration and low zero-speed output voltage generator. The ratio-type speed-measuring generator is a speed-sensitive output voltage (the fundamental output voltage component of the output voltage as a function of speed. It is numerically equal to the fundamental output voltage measured in two directions of rotation at the same speed and test conditions) 1/2 of the sum) Asynchronous speed-measuring generator with high zero-speed output, low rotor inertia, and high linearity of output voltage over the entire speed range. Integral-type speed-measuring generator is an asynchronous speed-measuring generator with small deviation of output voltage with temperature change and short heating time. It usually has a temperature control and compensation network.
If DC is applied to the field winding of the asynchronous speed-measuring generator, the direct-axis magnetic flux will no longer pulsate and become a constant magnetic flux. When the rotation speed is constant, the quadrature-axis magnetic flux generated by the cutting electromotive force is also constant, so no electromotive force is generated in the output winding. When the rotation speed changes, the magnitude of the cross-axis magnetic flux will change with the change of the rotation speed. It cross-links the output winding and generates an electromotive force proportional to the rotor acceleration. Therefore, it is fed into the excitation winding of the asynchronous speed generator. DC becomes an acceleration detector.
The permanent magnet type does not require an excitation power source, and the rotor is permanent magnet excitation, which has the advantages of simple structure and easy maintenance, but the number of poles is relatively small, and the ripple after the diode rectification is relatively large, and the filtering is difficult.
The inductive type works according to the principle of induced electromotive force generated by the variable reluctance effect between the stator and the rotor. The number of poles is relatively large, and the ripple after rectification is small and easy to filter, but the structure is complex and difficult to maintain. The above two types of speed-measuring generators can both use the amplitude of the output voltage to reflect the speed, and the frequency of the output voltage to represent the speed. The former is an analog quantity, which requires rectification and filtering; the latter is a digital quantity, which can be directly input to a microprocessor. If the amplitude and frequency are used together, it is possible to achieve high-sensitivity speed detection, but the direction of rotation cannot be determined, which is not as good as a DC speed generator. The pulse type uses a pulse frequency as an output signal and can be directly input to a microprocessor. It is a type with a smaller number of pulses per retransmission in a speed measurement code disc.