JP5006270B2 - Absolute encoder device and its operation method - Google Patents

Description

The present invention relates to an absolute encoder device and an operation method thereof, and more particularly to a high-precision absolute encoder device that provides absolute position information in a power failure state and an operation method thereof.

Conventional AC servo motors generally include an optical encoder for detecting rotor angle information, and the stator drive current can be determined using this angle information. Therefore, the speed of the AC servo motor can be accurately controlled.

FIG. 1 shows a schematic diagram of a prior art AC servomotor. The rotor angular position of the motor 10 is detected by the optical encoder 12 and processed by the signal processor 20 to obtain angle information. The angle information is processed by the speed estimator 14 to obtain the estimated motor rotation speed. The speed control device 30 receives an estimated motor rotation speed and speed command for controlling the control module 32 and an IGBT module 34 for generating a motor speed control signal. Using the motor speed control signal, the rotational speed of the motor 10 can be precisely controlled.

Particularly in the servo motor, the position sensor attached to the motor shaft is the optical encoder 12. The position accuracy of the servo motor depends on the resolution of the optical encoder, and the optical encoder 12 can be classified into an incremental encoder and an absolute encoder.

The incremental encoder can provide information about the previous position, and the absolute position of the encoder wheel can be known after a power failure unless it is reset. Therefore, the incremental encoder cannot know the absolute position (that is, the absolute angle) of the encoder wheel immediately after the power supply is restored and then restored again. On the other hand, the absolute encoder can always know the absolute position of the output shaft without suffering from a power failure. After the recovery from the power failure, the reset operation is not necessary and the operation is simplified.

FIG. 2 shows a schematic diagram of an optical encoder. The light from the light source 260 reaches the optical sensor 240 after passing through the rotating wheel 200 and the fixed mask 220. The signal received by the optical sensor 240 varies depending on the position change of the rotating wheel 200. Therefore, the position change of the rotating wheel 200 can be known by detecting the signal intensity of the optical sensor 240.

FIG. 3 shows a schematic diagram of an absolute encoder wheel 300 of a 6-bit encoder wheel. The absolute encoder wheel 300 includes a circular wheel body 302 and a plurality of grids 304. The grid 304 is in the innermost orbit, the first grating 304A occupying 1/2 of the circumference, the second inner orbit, two second gratings 304B each occupying 1/4 of the circumference, the third The grid 304C, the fourth grid 304D, the fifth grid 304E, and 32 sixth grids 304F that are in the outermost orbit and each occupy 1/64 of the circumference are included. The intensity change signal can be obtained along the radial direction and a position resolution of 2 ⁶ = 64 can be achieved along the circumferential direction. However, in order to improve the 1-bit resolution with the absolute encoder wheel 300 shown in FIG. 3, it is necessary to start another bit. When more resolution is required, the absolute encoder wheel 300 occupies more space than in FIG.

FIG. 4A shows a schematic diagram of an encoder wheel 400 for an incremental optical encoder comprising a circular wheel body 402 and a plurality of gratings. The lattice includes a main lattice 404A, a first lower lattice 404B, and a second lower lattice 404C, and the first lower lattice 404B and the second lower lattice 404C are arranged at two opposing positions of the main lattice 404A. FIG. 4B shows a mask 420 associated with the encoder wheel 400 comprising four rows of grids 420A.

FIG. 4C shows an optical sensor device 440 associated with the encoder wheel 400 comprising main sensor devices 442A, 444A, 442B, 444B (labeled A + / B + / A− / B−) corresponding to the main grid 404A. Show. As the encoder wheel 400 rotates, the main sensor devices 442A, 444A, 442B, 444B (labeled A + / B + / A- / B-) generate four sinusoidal signals. Signals such as four sine waves have a phase of 0/90/180/270 degrees, respectively. The A + / A− signal having a phase difference of 180 degrees is subtracted to obtain a sine wave signal A without common mode noise. The B + / B− signals having a phase difference of 180 degrees are subtracted to obtain a cosine wave signal B without common mode noise. Using the sine wave signal A and the cosine wave signal B having a phase difference of 90 degrees, it is possible to determine forward rotation or reverse rotation.

The incremental optical encoder can obtain incremental position information based on the sine wave signal A and the cosine wave signal B. In order to obtain absolute position information, origin sensor devices 446A, 446B (Z + / Z−) are additionally provided. However, after power recovery from a power failure, the origin mark on the incremental encoder should be detected by the origin sensor device to obtain absolute position information. This process is time consuming and is not suitable for applications that do not require returning to the origin mark.

In order to solve the problem of the absolute position at the time of a power failure, two attempts have been proposed in the prior art.
1. Mechanical count:
A gear set comprising a plurality of interengaging gears is provided for counting the number of rotations. FIG. 5 shows an example of a mechanical encoder, in which the spindle is connected to the first gear and the first gear is connected to the second gear.

An absolute code is marked on each gear, and the gear is assumed to provide n absolute positions after one revolution. A separate laser diode and photodiode are used to detect the absolute code. In addition, the gear set can identify n × n × n rotations of the spindle.

2. In an absolute encoder power failure condition that counts the rotation with the battery, the battery supplies power to the dedicated chip. The dedicated chip triggers the laser diode at a predetermined time, and the photodiode can detect absolute position information and then counts the number of revolutions in the forward and backward directions.

After normal power is supplied to the encoder again, the dedicated chip knows the accumulated rotational speed and the current absolute position information. Absolute position information can be improved by interpolation. However, absolute position information has an error at the boundary. Furthermore, the powder on the encoder wheel causes measurement errors. Therefore, accurate absolute position information should be checked at a specific calibration point. In other words, accurate absolute position information cannot be obtained immediately after normal power is restored.

An object of the present invention is to provide a high-precision absolute encoder device that provides absolute position information in a power failure situation and an operation method thereof.

Therefore, the high-precision absolute type absolute encoder device of the present invention is electrically connected to the incremental type encoder, and is electrically connected to the incremental type encoder output, the control unit for generating the control signal to the incremental type encoder, and the first pulse signal A comparator for generating, a latch device electrically connected to the comparator output, and generating a second pulse signal by latching the generated first pulse signal is included. When a power failure occurs, the control device generates a control signal as a continuous pulse of a predetermined time in order to drive the latch device and the incremental encoder. Therefore, the control device knows the angle information of the incremental encoder by counting the second pulse signal. The absolute type information can be obtained by combining the power failure angle information and the initial position.

The features of the invention believed to be novel are illustrated by the specificity of the appended claims. However, the invention itself is best understood by reference to the following detailed description of the invention, which, along with the accompanying drawings, describes exemplary embodiments of the invention.

In this invention, the resolution of the absolute position information is improved by generating A and B pulses similar to those of the incremental encoder instead of counting the number of rotations. Therefore, the absolute position information is obtained by counting the A and B pulses in both the power supply failure period and the normal power supply period in order to improve the resolution.

FIG. 6 shows a schematic diagram of a high-precision, absolute encoder device 60 of the present invention. The encoder device 60 includes a control device 100, a power switch 120, an incremental encoder 140, a comparator 160, a latch device 180, and a battery (not shown, providing Vcc), where the battery is shown in FIG. Power can be provided to other components. Incremental encoder 140 is a conventional incremental encoder such as that shown in FIG. 2 and includes a laser diode LD, a photodiode PD, and an encoder wheel (not labeled). The control device 100 is electrically connected to the power switch 120 and provides a control signal SW to the power switch 120 so that the laser diode LD is lit continuously (as described in detail later, normal mode or pseudo). Mode) or pulse system (battery mode), and selectively controlled to light continuously. Further, the control device 100 is electrically connected to the comparator 160 and the latch device 180. The photodiode PD generates a 0/180 phase signal (A +, A−) and a 90/270 phase signal (B +, B−); and the comparator 160 generates a first pulse signal A1 and B1, The signal output from the diode PD is processed. The first pulse signals A1 and B1 are processed by the latch device 180 to generate the second pulse signals A2 and B2. The second pulses A2 and B2 are processed by the counter 102 of the control device 100 to obtain incremental position information. Therefore, the control device 100 knows the absolute position information of the encoder wheel with reference to the incremental position information after the power failure and the initial position information immediately before the power failure.

FIG. 7 shows waveforms associated with the encoder device 60 of FIG. The control device 100 has a firmware design or a logic design for generating the control signal SW shown in FIG. When the state of the control signal SW is “high”, the laser diode LD is turned on. The photodiode PD generates a pulse signal according to the light passing through the encoder wheel and the mask of the encoder device 60. The pulse signal (A + / B + / A− / B−) of the photodiode PD is differentially processed by the comparator 160 to obtain the first pulse signals A1 and B1. The latch device 180 processes the first pulse signals A1 and B1 under the control of the control signal SW in order to generate the second pulse signals A2 and B2. The second pulse signals A2 and B2 are equivalent to the first pulse signals A1 and B2 during continuous lighting of the laser diode LD. The second pulse signals A2 and B2 have a shorter width when the encoder wheel has a faster rotational speed, which will be described later.

The control signal SW is used to generate the first pulse signals A1 and B1, so that the control signal SW has a shorter width than that of the absolute encoder that counts the rotation with the battery. For example, if the rotation of the encoder wheel is 512 ppr and the rotation speed is 60 rpm, the widths of the first pulse signals A1 and B1 are 60 sec / 60/512 = (1/512) sec = 2 msec. The width of the control signal SW is 2/5 msec = 0.4 msec or less in order to accurately count the first pulse signals A1 and B1. The on-time (logical “high”) of the control signal SW depends on the response characteristics of the laser diode LD and the photodiode PD. When normal power is supplied, the control signal SW is continuously on to obtain position information (normal mode). When the power supply fails, the control device 100 switches to the battery mode as long as the rotation speed is sufficiently low, for example, 30 rpm or less. In the battery mode, the control device 100 continuously supplies pulses of 0.4 msec width and triggers the control signal SW so as to be intermittently turned on, so that power is supplied from the battery. The control device 100 uses the counter 102 to calculate the rotation speed. If the rotation speed of the encoder wheel is higher than 30 rpm in a power failure state, the control device 100 triggers the control signal SW so as to be continuously turned on, so that power is supplied from the battery. Therefore, the position information can be known precisely. When the rotation speed of the encoder wheel becomes lower than 30 rpm again due to a power failure, the control device 100 continuously turns on the control signal SW again in order to turn on and off continuously in a pulse shape with a width of 0.4 msec. Trigger. As shown in FIG. 7, the rotation speed of the encoder wheel is generally not high in a power failure state, and the control signal SW that is subsequently turned on in a pulse shape of 0.4 msec width is a count result of 88, 87, 86, 85 Is sufficient to generate Therefore, the control device 100 can know the absolute position by referring to the incremental position information after the power failure and the first position information before the power failure.

FIG. 8 is a flowchart for explaining the operation of the high-precision absolute encoder device according to the present invention. The power state is checked in step S100, and the control device 100 drives the control signal SW in the continuous on state when the power state is normal (S102). When the power supply fails (for example, the three-phase power supplied to the motor is abnormal), the rotation speed of the encoder wheel is not high, and the control device 100 switches the operation to the battery mode (S104). Drives the control signal SW in the form of continuous pulses. Thereafter, the control device 100 detects whether the rotation speed of the encoder wheel is greater than 30 rpm (S110). If the rotation speed of the encoder wheel is higher than 30 rpm, the control device 100 switches the operation to the pseudo-normal mode (S112). Here, the control device 100 drives the control signal SW in the continuous on state, so that power is supplied from the battery. Is done. Therefore, the position information of the encoder wheel can be known precisely. If the rotation speed of the encoder wheel is lower than 30 rpm, the control device 100 keeps the operation in the battery mode (S104).

In summary, the high-precision absolute encoder device according to the present invention has the following features:
1. The laser diode is driven in pulses under power failure conditions, and the rotation of the encoder wheel is not calculated with reference to absolute position. Therefore, the absolute encoder apparatus according to the present invention calculates the position information and can maintain the rotation speed by the pulse signals A and B generated similarly to the normal power supply state.
2. The pulse signals A and B generated by the pulse control signal are latched so as to imitate the pulse signal generated by the continuous on control signal. Therefore, the counter operates normally in a power failure state.
3. The width of the control signal can be changed to count pulses generated at different rotational speeds.

1 shows a schematic diagram of a prior art AC servomotor. A schematic diagram of an optical encoder is shown. A schematic view of an absolute encoder wheel is shown. 1 shows a schematic diagram of an encoder wheel for an incremental optical encoder. 4B shows a mask associated with the encoder wheel of FIG. 4A. 4B shows an optical sensor device associated with the encoder wheel of FIG. 4A. An example of a mechanical encoder is shown. The schematic of the high precision absolute encoder device 60 of this invention is shown. 6 shows a waveform associated with the encoder device 60 of FIG. 3 shows a flowchart for explaining the operation of the high-precision absolute encoder device according to the present invention.

Explanation of symbols

60: Encoder device
140: Incremental encoder
200: Rotating wheel
220: Fixed mask
240: Light sensor
260: Light source
300: Absolute encoder wheel
302, 402: Circular wheel body
304A-F, 420A: Lattice
400: Encoder wheel
404A: Main lattice
404B-C: Lower lattice
420: Mask
440: Optical sensor device
442A-B, 444A-B: Main sensor device
446A-B: Origin sensor device

Claims (8)

An absolute encoder device that obtains absolute position information in a power failure state by using a laser diode, an incremental encoder including an encoder wheel and a photodiode, and a battery,
A controller electrically connected to the incremental encoder and supplying a control signal to the incremental encoder;
A comparator electrically connected to the incremental encoder and processing an output of the incremental encoder to generate a first pulse signal;
A latch device electrically connected to the controller and to the comparator and controlled by the control signal to process the first pulse signal to generate a second pulse signal;
The control device is configured to determine angle information with reference to the first pulse signal when power is normally supplied to the absolute encoder device, and in a power failure state, the control device In order to know the absolute position information in the power failure state by calculating the second pulse signal and the angle information before the occurrence of the power failure, the control signal of the continuous pulse is transmitted and the second pulse signal is calculated. The first pulse signal in the normal power supply state and the second pulse signal in the power supply failure state have the same waveform, whereby the control device counts in the normal power supply state and the power supply failure state. An absolute encoder device having an operation principle . 2. The absolute encoder device according to claim 1, wherein the latch device latches the first pulse signal when the control signal is “high” in a power failure state. 3. 2. The absolute encoder device according to claim 1, wherein the control device transmits a control signal in a continuous “ON” state when the rotation speed of the encoder wheel is greater than 30 rpm. The absolute encoder apparatus according to claim 1, wherein the encoder wheel has a resolution of 512ppr, and the control signal of the continuous pulse has a width of 0.4msec. A method for obtaining absolute position information in a power failure condition using an incremental encoder and battery comprising a laser diode, an encoder wheel and a photodiode, comprising:
In normal power condition, to obtain the first pulse signal, compare the incremental encoder output,
When the rotational speed of the incremental encoder is lower than a predetermined threshold in a power failure state, the incremental encoder is driven by a continuous pulse control signal, and the incremental encoder is driven by the control signal to cause a power failure state. to generate a first pulse signal in;
Latching the first pulse signal in a power failure state under the control of the control signal to generate a second pulse signal;
Positional information of the incremental type encoder calculated based on the second pulse signal and the power failure before the angle information,
The first pulse signal in the normal power supply state and the second pulse signal in the power supply failure state have the same waveform, so that the control signal has the same counting operation principle in the normal power supply state and the power supply failure state. A method characterized by. 6. The method of claim 5, further comprising transmitting the control signal as a continuous “on” signal when the rotational speed of the incremental encoder is above a predetermined threshold in a power failure condition. The method of claim 5, wherein the predetermined threshold is 30 RPM. 6. The method of claim 5, wherein the encoder wheel has a resolution of 512 ppr and the continuous pulse control signal has a width of 0.4 msec.

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