What is meant by detent torque?
What is meant by detent torque?
Stated another way, detent torque is the amount of torque the motor produces when the windings are not energized. The effect of detent torque can be felt when moving the motor shaft by hand, in the form of torque pulsations or cogging.
What causes detent torque?
The detent torque exists because of the residual magnetism in the Permanent magnetic material used for the construction of the rotor of the motor. It is produced when the stator coils are not energised. This torque prevents the rotor from Drifting when the motor supply is turned off.
How is detent torque calculated?
Detent torque is calculated as the differential of the magnetic coenergy with respect to rotor angular position at constant rotor excitation. Validation of the detent torque equation is performed by comparing results obtained from the proposed method with laboratory test results.
Do BLDC motors have constant torque?
As discussed earlier, in a BLDC motor, the torque remains constant for a speed range up to the rated speed. The motor can be run up to the maximum speed, which can be up to 150% of the rated speed, but the torque starts dropping.
What is maximum holding torque?
The stepper motor holding torque refers to the maximum torque that the stepper motor can output when the motor’s phase windings pass the rated current and is in the static lock state. It is one of the most important parameters of a stepper motor. m stepper motor normally means the holding torque is 2N.
How much holding torque do I need?
Holding torque is not usable torque and should be approximately halved if operating torque is not given. Ultimately the amount of torque depends on how much power (like watts power) you’re pumping into your steppers. The rating on the steppers are based on their optimal; however you can over drive them.
What is the effect of cogging torque?
Cogging torque is an undesirable component for the operation of such a motor. It is especially prominent at lower speeds, with the symptom of jerkiness. Cogging torque results in torque as well as speed ripple; however, at high speed the motor moment of inertia filters out the effect of cogging torque.
Do servos have holding torque?
Unlike stepper motors, they do not have holding torque per se. The combination of speed and torque enables servo motors to deliver better acceleration than stepper motors. They also deliver improved positioning accuracy as a result of closed-loop operation.
How much torque do I need in a motor?
To calculate load torque, multiply the force (F) by the distance away from the rotational axis, which is the radius of the pulley (r). If the mass of the load (blue box) is 20 Newtons, and the radius of the pulley is 5 cm away, then the required torque for the application is 20 N x 0.05 m = 1 Nm.
When does torque drop off in a BLDC motor?
During continuous operations, the motor can be loaded up to the rated torque. In a BLDC motor, the torque remains constant for a speed range up to the rated speed. The motor can be run up to the maximum speed, which can be up to 150% of the rated speed, but the torque starts dropping off.
Why does detent torque have to be overcome?
Because detent torque has to be overcome before the motor will move, it reduces the ideal torque the motor can produce when it’s running. The amount of power the motor needs to produce to overcome the detent torque is proportional to the motor’s speed.
How are the windings distributed in a BLDC motor?
Traditionally, the stator resembles that of an induction motor; however, the windings are distributed in a different manner. Most BLDC motors have three stator windings connected in star fashion. Each of these windings are constructed with numerous coils interconnected to form a winding.
Why do brushless servo motors have high detent torque?
With a high torque-to-inertia ratio, less torque is wasted accelerating the rotor, and more torque is available for accelerating the load. Many servo motors that have high torque for their size are afflicted with high detent torque (the unenergized servo motor wants to lock onto certain positions more than others).