Mr. Vex: Dear Miss Ori, i know this is very fundamental but i need to ask you about the overrun of motors.
Miss Ori: what is it, vex?
Mr. Vex:Well, "over-run" refers to number of excess to rotations that motors makes from the instant the power is cut off to that time that is actually stops.It is normally indicated either by an angle or by revolutions, am i correct?
Miss. Ori:That's right. The larger the load inertia moment, the larger the overrun.
Mr. Vex: Oh? the load moment of inertia is related?
Miss. Ori: Yes, for instance, when two lorries are running at the same speed and were to stop suddenly, the loaded lorry will need longer distance to come to a complete stop in comparison to the other lorry without any load. For the same theory, over run of the motor with larger load inertia movement becomes larger.
Mr. Vex:I see, so generally, what is the motor over run?.
Miss. Ori: It differs from by motor type too. The overrun of the induction motor without load moment of inertia will be about 30~40 revolutions.
Mr. Vex:Overrun varies by the motor type?
Miss. Ori:Yes, reversible motor has approximately 5-6 revolutions for the over run.
Mr. Vex:Why does the reversible motor has smaller overrun than the induction motors.
Miss. Ori: Because the reversible motor has a built-in simple brake system, which enhances instant switching of rotating direction. That's is why it has smaller over turn compared to the induction motor.
Mr. Vex:Ok, by the way , what kind of brake is the simple brake system?
Miss. Ori: It has brake shoe that will pressed onto a brake plate, which is fixed on the motor.
Mr. Vex:Hmm, so the overrun is reduce to the simple brake system!. Then what happen to overrun when gear head is used?
Miss. Ori:That's is a good question! The actual over run is reflected by the number of motor shaft rotations.Therefore, the over run of output shaft when gear head is used is "1/ratio of gear head".
Mr. Vex:So, if the gear head with reduction ratio 1:3 is used in induction motor, it's gear head is output shaft overrun will be 10~13 revolutions.
Miss. Ori:Exactly. The larger gearhead reduction ratio, the smaller the over run. But since it's solution speed would be reduced to 1/ratio of gearhead, operation speed would be slower too. In other words, production volume will be reduced. This is the important fact, which customer needs to be consider very carefully. If the speed is preferred to be the same and to achieve smaller overrun, the electromagnetic brake motor or brake pack should be used.
Mr. Vex:Oh yes! You have taught me that before! The electromagnetic brake motor that can achieve holding torque or brake-pack to instantly stop the rotation by inducing braking current.
Miss. Ori:That is it. Overrun of the motor with electromagnetic brake is about 2~3 revolutions, the brake pack is 1~1.5 revolutions.
Mr. Vex:Yes, now i remembered. I do not know overrun varies so much by motor type.
Miss. Ori:That is why motor should have chosen considering usage purpose. Remember it is very important to find out the usage conditions to recommend suitable motors for our customers.Mr. Vex: Definitely. Thanks Miss Ori.