Understand the determination of the moment of inertia of variable frequency motor
Moment of inertia is a measure of the inertia (the characteristic that a rotating object maintains its uniform circular motion or stationary) when the rigid body rotates around the axis. It is one of the indicators for measuring the responsiveness and flexibility of the motor. The magnitude depends on the shape of the object, the mass distribution, and the position of the shaft. It can be said that the inertia of an object for rotational motion. The role of moment of inertia in rotational dynamics is equivalent to the mass in linear dynamics, describing the relationship between angular momentum, angular velocity, moment and angular acceleration.
The moment inertia measurement of the variable frequency motor of the MATFT reducer includes the suspension rotor oscillating method, the no-load deceleration method and the auxiliary pendulum method. This paper introduces the test contents of the three kinds of rotational inertia test methods of the variable frequency motor according to the relevant motor test standards.
1. Measuring the moment of inertia by the suspension rotor swing method
1. Single wire method for measuring moment of inertia
The moment of inertia of the rotor of the motor is measured by a single wire torsion swing comparison method.
A dummy rotor is made of a metal having a uniform density, and the shape of the dummy rotor should be a simple cylinder so that the moment of inertia of the false rotor can be accurately calculated by the formula (1). The quality of the dummy rotor should be such that the selected wire is straightened and the wire is not deformed. The dummy rotor is reliably suspended at one end of the wire with a length of l ≥ 0.5 m, and the other end of the wire is fixed to the bracket, and the wire axis should be concentric with the axis of the dummy rotor and perpendicular to the ground.
The dummy rotor is twisted around the mandrel at an appropriate angle, and the number N of reciprocating oscillations and the required time t(s) are carefully measured to obtain an average value of the oscillation period T' (T' = N/t). Under the same conditions, the above test is repeated under the same conditions, and the average value T of the oscillation period is obtained according to the above method, and the moment of inertia J of the motor to be tested is calculated according to the equation (2).
2, double wire method to determine the moment of inertia
Suspend the rotor of the motor under test with two parallel wires so that the centerline of the shaft is perpendicular to the ground. The rotor is twisted to produce an axis-centered oscillation. The torsion angle from the centerline of the shaft should be no more than 10°.
2, the no-load deceleration method to determine the moment of inertia
This method is used to measure the moment of inertia of a machine with a power of 100 kW or more.
3, the auxiliary pendulum method to determine the moment of inertia
This method is used to determine the moment of inertia of a motor with a rolling bearing.
An auxiliary pendulum of known quality is fixed to the center of the end face of the shaft of the test motor with the arm of the smallest possible mass. The pendulum arm should be at right angles to the axis. They can also be used to hold the pendulum when there are pulleys or half couplings on the shaft.
