Mr. Vex: Miss Ori, i got a request from product selection from our customer.The servo motor vibrates and alarm goes off.
Miss Ori:It is hunting.
Mr. Vex: What is hunting?
Miss Ori: Servo motors control method is called closed loop control and it monitors the difference of input pulse and pulses which the encoder at the back of a motor feedback. The difference is called a deflection, and a servo motor is controlled to maintain the deflection at zero all the time. Forward and reverse rotation are repeated to maintain the deflection at zero especially when the load inertia becomes large, and alarm may go off due to strong vibration.
Mr. Vex: If that is the case, what cam be done to reduce vibration?
Miss. Ori:Have you tried gain tuning?
Mr. Vex:What do you mean by gain tuning?
Miss. Ori: It is to adjust to optimize the closed loop control, depending on amount of load inertia. If this adjustment is not properly done, it will cause strong vibration when the motor is stopped and the motor in motion cannot operate smoothly. The adjustment varies depending on the rigidity of the mechanism such as belt pulley or screw mechanism.
Mr. Vex:Gain turning sounds somehow difficult. How about stepping motor unit, which is a closed loop stepping motor?
Miss. Ori: It has features of both easy use of stepping motor and reliability of servo motor. It can correspond to sudden load changes and sudden acceleration because it does not need gain tuning like servo motor and changing over from open loop to closed loop control is automatically done immediately when loss of synchronization is about to occur.
Mr. Vex:Sounds good for it's easy use. By the way, just now you said "gain tuning for servo motor depends on volume of load inertia". How much load inertia can a servo motor or stepping motor move?
Miss. Ori:Well, in terms of the ratio of load inertia to rotor inertia, it is said that this inertia ratio for stepping motor should not be more than 10. For servo motor and step inertia ratio should not be more than 30. But different sizes of motor have different allowable inertia ratio. Therefore, it is advisable to compare the actual inertia ratio values for the sizes of motor.
Mr. Vex:There are various differences depending on motors. There are so much to learn.
Miss. Ori: MMr.Vex, do learn about characteristics of motors one by one. You need to be able to recommend the most suitable motors by listening to what are your customer's applications. Moreover, it is necessary to do calculation correctly to choose an optimal motor. Therefore, do advise your customers about our "motor sizing service", where we are able to do the time consuming calculations for them.
Mr. Vex:Okay. I will do my best so that i can understand the calculation myself in order to explain to my customers. But there is so much to learn and my alarm may go off.