Commonly used servo motor speed sensors are divided into numbers and analog types. The digital has a photoelectric encoder, a magnetic encoder; the analog has a speed measuring motor; and the other is a rotary transformer, which is essentially an analog type, but usually processes its signal into a digital type, so it is also It comes down to a digital speed sensor. The speed measurement methods mentioned in this paper are all specific methods for obtaining speed information by processing digital pulse signals.

There are three general speed measurement methods: M method, T method, and M/T method.

  1. Introduction to the M method:

(1) M method: Open a time window, the number of encoder pulses in this time window, the faster the speed, of course, the more the number of pulses for the time window.

(2) Angular velocity calculation: Angular velocity refers to the average angular velocity within the time window.

Angular velocity = K× number of pulses K is a constant coefficient

(3) Accuracy: If the number of pulses in the time window is N, the maximum absolute error is 1 pulse, then the theoretical relative error is 1/N. There is a small trick to reduce this error, that is, if the number of pulses is N, then change it to N+0.5. The maximum error at this time = 1/2N.

(4) Features:

a. The larger the time window, the higher the accuracy, but the greater the pure delay caused by the measurement

b. In the case where the time window is unchanged, the slower the rotation speed, the larger the error.

  1. Introduction to the T method:

(1) T method: The encoder pulse is used as the time window. In this time window, the number of pulses of the timer clock source is also known as the capture mode. The faster the speed, the shorter the time window of the encoder and the fewer the number of pulses.

(2) Angular velocity: An angular velocity is the average angular velocity within a time window.

Angular velocity = K/N, where K is the constant coefficient

(3) Accuracy: The maximum error is also a pulse. Relative error = 1 / (N + 1)

(4) Features: The lower the speed, the higher the accuracy, but the greater the pure delay caused by the measurement

  1. Introduction to M/T method:

(1) M/T method: This method is similar to the T method. The difference is that the T method uses one encoder pulse as the time window, and the M/T method uses m encoder pulses as the time window, and the number of timer clock sources. The number of pulses.

(2) Angular velocity: An angular velocity is the average angular velocity within a time window.

Angular velocity=Km/N, where K is a constant coefficient, m is the number of encoder pulses that make up the time window, and N is the number of timer clock source pulses to which the time window counts.

(3) Features: Compared with the T method, the M/T method can improve the measurement accuracy at high speed, but correspondingly increases the pure delay.

Leave a Reply

Your email address will not be published. Required fields are marked *