1. The measurement object of the encoder
The way in which the encoder measures the linear displacement
(1) The encoder is installed at the end of the lead screw
By measuring the angular displacement q of the ball screw, the linear displacement x of the worktable is indirectly obtained, and a semi-closed-loop servo system is formed.
(2) Lead screw pitch
Let the pitch t=4mm, the lead screw rotates 10 times in 4s, find out: the average speed of the lead screw n(r/min) and how many mm does the nut move?
(3) The encoder and servo motor are coaxially mounted
(4) The encoder and servo motor are coaxially mounted
(5) The encoder and servo motor are coaxial mounted
(6) Comparison of the two installation methods of the encoder
What is the difference between the position control accuracy of the encoder mounted at the end of the lead screw and the front end (coaxial with the servo motor)?
2. Absolute Measurement (ABS)
(1) Signal nature
Outputs n-bit binary codecs, each corresponding to a unique angle.
(2) Contact absolute disc
(3) Absolute photoelectric code disc
3. Incremental Measurement (INC)
(1) Signal nature
(2) The structure of the incremental optical encoder
(3) Orientation
The signals A and B generated by the photosensitive element are 90° phase different from each other and are used for direction discrimination. When the disc rotates, signal A is ahead of signal B by 0°, and when the disc is reversed, signal B is 90° ahead of signal A.
(4) Direction signal
(5) Frequency doubling (subdivision)
Under the condition of existing encoders, the resolution of the encoder can be improved by subdividing technology. Before subdivision, the resolution of the encoder is only the size of the resolution angle. After adopting the 4-segmentation technology, the frequency of the counting pulse is increased by 4 times, which is equivalent to a 3-fold increase in the resolution of the original encoder, and the measurement resolution angle is 1/4 of the original, improving the measurement accuracy.
(6) Zero mark (one turn pulse)
In the disc circle, there is also a slit C, which generates a pulse per revolution, which is also called a "one-turn signal" or zero flag pulse, which serves as the starting reference for the measurement.
(7) The role of the zero flag in the return reference point
(8) Return to the reference point deceleration switch
(9) Back to the reference point schematic diagram
Fourth, the application of encoder in digital speed measurement
(1) Comparison of analog speed measurement and digital speed measurement
(2) M method speed measurement (suitable for high speed occasions)
There is an incremental optical encoder with a parameter of 1024p/r, and 65536 pulses are measured in 5 seconds, then the rotational speed (r/min) is: n = 60 × 65536 / (1024 × 5) = 768 r/min
The encoder generates N pulses per revolution, and if there are m1 pulses in the T time period, the rotational speed (r/min) is: n = 60m1/(NT)
(3) T method speed measurement (suitable for low speed occasions)
There is an incremental optical encoder with a parameter of 1024p/r, the number of pulses between two adjacent pulses is measured to be 3000, and the clock frequency fc is 1MHz, then the rotational speed (r/min) is:
n = 60fc /（Nm2 ）=60×106/（1024×3000）=19.53 r/min
The encoder generates N pulses per revolution, with a known frequency fc as the clock, and the number of pulses between the two adjacent pulses that fill into the encoder output is m2, then the rotational speed (r/min) is: n = 60fc / (Nm2)
5. The application of encoder in spindle control
(1) Spindle encoder
(2) The spindle encoder is used for C-axis control
(3) The spindle encoder is used for thread turning
When turning threads, in order to ensure that the starting point of each cut remains unchanged and prevent "messy teeth", the spindle encoder achieves the purpose of turning threads by counting the pulses between the starting point and the retracting point.
brief summary
(1) The encoder is used to measure the angular displacement. In the linear feed motion control of CNC machine tools, the linear displacement is indirectly measured by measuring the angular displacement.
(2) The absolute encoder outputs binary encoding, and the incremental encoder outputs pulses.
(3) The output signal of the incremental encoder should be processed with direction recognition, zero flag and frequency doubling.
(4) The encoder is used for digital speed measurement, including M method and T method, and is used for C-axis control and thread cutting in CNC lathes.