A photoelectric rotary encoder system and a rotation speed measurement method thereof

Abstract

The present invention relates to a photoelectric rotary encoder system and a rotational speed measurement method thereof, characterized by: a front-stage optical code disk fixed to an input shaft, a rear-stage optical code disk fixed to a differential shaft, a permanent magnet synchronous motor shaft coaxially fixed to a power shaft; one end of each of the three shafts is connected to the three shafts of a differential module; the differential shaft speed is equal to the sum of the power shaft speed and the input shaft speed; the other end of the input shaft is fixed to the measured shaft; a three-phase sinusoidal drive circuit is used to generate a three-phase sinusoidal voltage to drive the permanent magnet synchronous motor to rotate at a constant speed; the front-stage and rear-stage measurement circuits respectively convert the rotation of the front-stage and rear-stage optical code disks into pulse signals, which are respectively collected and resolved by a single-chip microcomputer; the front-stage measurement circuit signal is directly resolved using a time-recording method or a distance-recording method to obtain the measured shaft rotational speed; after the rear-stage measurement circuit signal is resolved, the single-chip microcomputer system subtracts the speed difference caused by the power shaft to obtain the measured shaft rotational speed. The present invention achieves both accurate and rapid rotational speed measurement.

Description

Technical Field

[0001] The invention belongs to the field of rotational speed measurement in measurement and control technology, and particularly relates to a photoelectric rotary encoder system and a rotational speed measurement method thereof. Background Art

[0002] The speed measurement technology based on photoelectric rotary encoder has a wide range of applications in industry. Through the photoelectric rotary encoder, the rotational angular velocity of the rotating shaft can be converted into a pulse electrical signal, which can be further collected and solved by the single-chip microcomputer to achieve the speed measurement.

[0003] There are generally two methods for digital measurement of the output signal of a photoelectric rotary encoder. One is the distance counting method (M method), which uses a single-chip microcomputer to count the encoder output pulses within a fixed time interval to calculate the rotational speed. The other is the time counting method (T method), which uses a single-chip microcomputer to measure the time interval between two adjacent encoder pulse outputs to calculate the rotational speed.

[0004] With traditional photoelectric encoders, when the shaft speed is low, the encoder output pulse signal frequency is low. The distance-measuring method results in a large relative error in speed measurement due to the small number of pulses per unit time. The time-measuring method results in a low speed measurement frequency due to the long interval between two adjacent pulses. Consequently, at low speeds, traditional solutions struggle to achieve both accurate and frequent measurements. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a photoelectric rotary encoder system and a rotation speed measurement method thereof.

[0006] One of the above-mentioned purposes of the present invention is achieved through the following technical solution:

[0007] A photoelectric rotary encoder system, characterized by comprising: a front-stage optical code disk, a front-stage measurement circuit, a rear-stage optical code disk, a rear-stage measurement circuit, a differential module, a permanent magnet synchronous motor, a three-phase sinusoidal drive circuit, an input shaft, a power shaft, and a differential shaft;

[0008] The front-stage optical code disk is coaxially fixed to the input shaft, the rear-stage optical code disk is coaxially fixed to the differential shaft, and the permanent magnet synchronous motor shaft is coaxial and fixed to the power shaft;

[0009] One end of the input shaft, power shaft, and differential shaft are connected to the three shafts of the differential module respectively; the speed of the differential shaft is equal to the sum of the speed of the power shaft and the speed of the input shaft;

[0010] The other end of the input shaft is fixedly connected to the external measured rotating shaft to measure the rotation speed of the measured rotating shaft;

[0011] The three-phase sinusoidal drive circuit is used to generate a three-phase sinusoidal voltage to drive the permanent magnet synchronous motor to rotate at a constant speed;

[0012] The front-stage measurement circuit and the rear-stage measurement circuit convert the rotation of the front-stage optical code disk and the rear-stage optical code disk into pulse signals respectively, which are collected and solved by the single-chip microcomputer respectively. The front-stage measurement circuit signal is directly solved by the time method or the distance method to obtain the measured shaft speed. After the rear-stage measurement circuit signal is solved, the single-chip microcomputer system subtracts the speed difference caused by the power shaft to obtain the measured shaft speed.

[0013] The second object of the present invention is achieved by the following technical solution:

[0014] A rotational speed measurement method based on the above-mentioned photoelectric rotary encoder system is characterized in that: when the encoder is working, the single-chip microcomputer collects data of the front-stage pulse signal according to the distance recording method and the time recording method respectively, and collects data of the rear-stage pulse signal according to the time recording method, and selects a solution method for the final output rotational speed value based on the collected data results. The judgment method for selecting the final output rotational speed value is:

[0015] When the speed value is high and the error of the distance method of the front-stage measurement circuit is lower than the error of the time method, the speed value calculated by the distance method of the front-stage measurement circuit is used as the output value; when the speed value is medium, the error of the time method of the front-stage measurement circuit is lower than the error of the distance method and the measurement frequency meets the requirements, the speed value calculated by the time method of the front-stage measurement circuit is used as the output value; when the speed value is low, the error of the time method of the front-stage measurement circuit is lower than the error of the distance method but the measurement frequency does not meet the requirements, the speed value calculated by the time method of the rear-stage measurement circuit minus the speed value of the power shaft is used as the output value.

[0016] Further: define the number of gratings on the two optical code disks (i.e. the number of pulses output by the measuring circuit when the optical code disk rotates one circle) as n e , the MCU timer clock frequency is f c (Unit: Hz), the system's minimum speed measurement frequency is f s (unit is Hz), and f c >4f s , the external measured speed, i.e. the input shaft speed, is sp1 (in revolutions per second), the permanent magnet synchronous motor speed, i.e. the power shaft speed, is sp m (Unit is revolutions per second); define the speed measurement frequency of the odometry method as f u1 =f s (Unit is Hz), the number of pulses in the measurement time interval when the front-stage signal is measured by distance measurement is n1, and the frequency of the time measurement is defined as f u2 (Unit is Hz), when measuring speed by time recording method of front-stage signal and back-stage signal, the count values ​​of single-chip timer between two adjacent pulse signals are n2 and n3 respectively; then:

[0017] The speed expression of the front-stage measurement circuit is:

[0018]

[0019] The relative error expression of speed measurement by the path-measuring method of the front-stage measurement circuit is:

[0020]

[0021] The time-recording method speed measurement expression of the front-stage measurement circuit is:

[0022]

[0023] The speed measurement error of the front-stage measurement circuit using the time-recording method is:

[0024]

[0025] The frequency expression of speed measurement by time-recording method of the front-stage measurement circuit is:

[0026]

[0027] The speed expression of the post-stage measurement circuit in time method is:

[0028]

[0029] When the error of the time method and the distance method of the front-stage measurement circuit are the same, the solution is

[0030]

[0031]

[0032] The time measurement frequency of the current level measurement circuit is equal to the minimum frequency f required by the system. s When

[0033]

[0034]

[0035]

[0036] The motor speed is set to sp m =f s / n e The method for selecting the final output speed value is:

[0037] When the system is running, when the speed is greater than That is, the microcontroller detects that the conditions are met or When the speed meets the requirement, the single chip microcomputer uses the front stage measurement circuit to record the speed expression of the distance method to output the speed; when the speed meets the requirement, the single chip microcomputer uses the front stage measurement circuit to record the speed expression ... That is, the microcontroller detects that the conditions are met or and n2≤f c / f s or n3≤f c / (f s +sp m *n e ), the single chip microcomputer uses the front stage measurement circuit to record the time method speed expression to output the speed; when the speed is less than f s / n e When the MCU detects that the condition n2>f is satisfied c / f s or n3>f c / (f s +sp m *n e ), the single chip computer uses the subsequent measurement circuit to record the speed expression using the time method to output the speed.

[0038] The present invention has the following advantages and positive effects:

[0039] The present invention ensures that at least one optical code disk maintains a relatively high rotation speed at extremely low rotation speeds by setting differential rotation of the two optical code disks. Different optical code disk output signals can be selected in different speed sections, and the final speed output value is obtained through different solution methods. This realizes the complementarity of the output signals of the front-end and rear-end optical code disks, thereby achieving a balance between the accuracy and speed of rotation speed measurement and improving the rotation speed measurement effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the structure of the photoelectric rotary encoder system of the present invention;

[0041] Figure 2 Schematic diagram of the differential module assembly of the photoelectric rotary encoder system of the present invention;

[0042] Figure 3 It is a schematic diagram of mode selection of the rotation speed measurement method based on the photoelectric rotary encoder system of the present invention. DETAILED DESCRIPTION

[0043] The structure of the present invention will be further described below with reference to the accompanying drawings and through examples. It should be noted that the present examples are descriptive rather than restrictive.

[0044] A photoelectric rotary encoder system, see Figure 1-2, including an input shaft 1, a differential shaft 2, a power shaft 3, a differential module 4, a front-stage optical code disk 5, a rear-stage optical code disk 6, a front-stage measurement circuit 7, a rear-stage measurement circuit 8, a permanent magnet synchronous motor 9, and a three-phase sinusoidal drive circuit 10, wherein the differential module includes a planetary bevel gear differential and a constant speed conversion gear.

[0045] One end of the input shaft, differential shaft, and power shaft are connected to the differential module respectively, such as Figure 2 The figure shows the component structure of the differential module, which includes a planetary bevel gear differential and a constant speed conversion gear. The planetary bevel gear differential is used to achieve speed conversion between the input shaft, power shaft, and differential shaft. The constant speed conversion gear does not change the speed and is only used to adjust the output direction of the shaft speed.

[0046] Define the speeds of the input shaft, differential shaft, and power shaft as sp1, sp2, and sp3, respectively, satisfying:

[0047] sp2=sp1+sp3 (1)

[0048] The front-stage optical encoder is fixed to the input shaft, the rear-stage optical encoder is fixed to the differential shaft, and the rotating shaft of the permanent magnet synchronous motor is coaxial with the power shaft and fixedly connected. The other end of the input shaft is fixedly connected to the external measured rotating shaft for measuring the speed of the measured rotating shaft;

[0049] The front-stage measurement circuit is used to convert the rotation of the front-stage optical code disk into a pulse signal output, and the rear-stage measurement circuit is used to convert the rotation of the rear-stage optical code disk into a pulse electrical signal output;

[0050] The three-phase sinusoidal drive circuit is used to generate a three-phase sinusoidal voltage to drive the permanent magnet synchronous motor to rotate at a constant speed. The number of pole pairs of the permanent magnet synchronous motor is defined as n, and the frequency of the sinusoidal signal generated by the three-phase sinusoidal drive circuit is f. m , the permanent magnet synchronous motor speed formula is:

[0051] sp3=f m / p (2)

[0052] The present invention provides a method for measuring the rotation speed of a photoelectric rotary encoder system. During operation, the rotation of an external measured shaft drives the input shaft to rotate at a certain speed, and a permanent magnet synchronous motor drives the power shaft to rotate at a constant speed. After differential processing by a differential module, the differential shaft always maintains a constant speed difference with the input shaft. As a result, the front-stage optical code disk rotates at the same speed as the external measured shaft, and the rear-stage optical code disk always maintains a constant speed difference with the front-stage optical code disk.

[0053] The front-stage measurement circuit and the back-stage measurement circuit output pulse signals, which are collected and solved by the single-chip microcomputer 11 respectively. The front-stage measurement signal is directly solved by the single-chip microcomputer through the distance method or the time method to obtain the measured shaft speed. After the back-stage measurement signal is solved by the single-chip microcomputer through the time method, the speed difference caused by the power shaft is subtracted to obtain the measured shaft speed.

[0054] Define the number of gratings on the two optical code disks (i.e. the number of pulses output by the measuring circuit when the optical code disk rotates one circle) as n e , the MCU timer clock frequency is f c (Unit: Hz), the system's minimum speed measurement frequency is f s (unit is Hz), and f c >4f s , the external measured speed, i.e. the input shaft speed, is sp1 (in revolutions per second), the permanent magnet synchronous motor speed, i.e. the power shaft speed, is sp m (Unit is revolutions per second); define the speed measurement frequency of the odometry method as f u1 =f s (Unit is Hz), the number of pulses in the measurement time interval when the front-stage signal is measured by distance measurement is n1, and the frequency of the time measurement is defined as f u2 (Unit is Hz), when measuring speed by time method of front-stage signal and back-stage signal, the count value of single chip timer between two adjacent pulse signals are n2 and n3 respectively;

[0055] The speed expression of the front-stage measurement circuit is:

[0056]

[0057] The relative error expression of speed measurement by the path-measuring method of the front-stage measurement circuit is:

[0058]

[0059] The time-recording method speed measurement expression of the front-stage measurement circuit is:

[0060]

[0061] The speed measurement error of the front-stage measurement circuit using the time-recording method is:

[0062]

[0063] The frequency expression of speed measurement by time-recording method of the front-stage measurement circuit is:

[0064]

[0065] The speed expression of the post-stage measurement circuit in time method is:

[0066]

[0067] Consider the existence of two critical states:

[0068] First, when the error of the time method and the distance method of the front-stage measurement circuit are the same, the solution is

[0069]

[0070]

[0071] Second, when the current level measurement circuit's time measurement frequency is equal to the system's minimum frequency f s When

[0072]

[0073]

[0074]

[0075] The motor speed is set to:

[0076]

[0077] Based on the above calculation, the speed switching scheme of the speed measurement method of the photoelectric rotary encoder system according to the embodiment of the present invention is as follows: Figure 3 As shown:

[0078] When the system is running, when the speed is greater than That is, the microcontroller detects that condition d is met: or When the speed meets the requirement, the single chip microcomputer uses the front stage measurement circuit to record the speed expression of the distance method to output the speed; when the speed meets the requirement, the single chip microcomputer uses the front stage measurement circuit to record the speed expression ... That is, the microcontroller detects that condition a is met: (or ) and satisfy the condition c:n2≤f c / f s (or n3≤f c / (f s +sp m *n e )), the single chip microcomputer uses the front stage measurement circuit to record the time method speed expression to output the speed; when the speed is less than f s / n e When the MCU detects that the condition b:n2>f is satisfied c / f s or n3>f c / (f s +sp m *n e), the single chip computer uses the subsequent measurement circuit to record the speed expression using the time method to output the speed.

[0079] This can satisfy the optimal selection output in each speed range.

[0080] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various replacements, changes and modifications are possible without departing from the spirit of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A method for measuring rotational speed based on a photoelectric rotary encoder system, characterized in that: The photoelectric rotary encoder system includes a front-stage optical code disk, a front-stage measurement circuit, a rear-stage optical code disk, a rear-stage measurement circuit, a differential module, a permanent magnet synchronous motor, a three-phase sinusoidal drive circuit, an input shaft, a power shaft, and a differential shaft; The front-stage optical code disk is coaxially fixed to the input shaft, the rear-stage optical code disk is coaxially fixed to the differential shaft, and the permanent magnet synchronous motor shaft is coaxial and fixed to the power shaft; One end of the input shaft, power shaft, and differential shaft are connected to the three shafts of the differential module respectively; the speed of the differential shaft is equal to the sum of the speed of the power shaft and the speed of the input shaft; The other end of the input shaft is fixedly connected to the external measured rotating shaft to measure the rotation speed of the measured rotating shaft; The three-phase sinusoidal drive circuit is used to generate a three-phase sinusoidal voltage to drive the permanent magnet synchronous motor to rotate at a constant speed; The front-stage measurement circuit and the rear-stage measurement circuit respectively convert the rotation of the front-stage optical code disk and the rear-stage optical code disk into pulse signals, which are respectively collected and resolved by the single-chip microcomputer. The front-stage measurement circuit signal is directly resolved by the time method or the distance method to obtain the measured shaft speed. After the rear-stage measurement circuit signal is resolved, the single-chip microcomputer system subtracts the speed difference caused by the power shaft to obtain the measured shaft speed. When the encoder is working, the single chip microcomputer collects data of the front-stage pulse signal according to the distance method and the time method respectively, and collects data of the rear-stage pulse signal according to the time method, and selects the solution method of the final output speed value according to the collected data results. The judgment method of selecting the final output speed value is: Define the number of gratings on the two optical code disks as n e , the MCU timer clock frequency is f c , the system's minimum speed measurement frequency is f s , and f c >4f s , the external measured speed, that is, the input shaft speed is sp1, the permanent magnet synchronous motor speed, that is, the power shaft speed is sp m ; Define the speed measurement frequency of the odometry method as f u1 =f s When the front-stage signal is measured by distance measurement, the number of pulses in the measurement time interval is n1, and the speed measurement frequency of the time measurement method is defined as f u2 , when measuring speed by the time method of the front-stage signal and the back-stage signal, the count values ​​of the single-chip timer between two adjacent pulse signals are n2 and n3 respectively; then: The speed expression of the front-stage measurement circuit is: The relative error expression of speed measurement by the path-measuring method of the front-stage measurement circuit is: The time-recording method speed measurement expression of the front-stage measurement circuit is: The speed measurement error of the front-stage measurement circuit using the time-recording method is: The frequency expression of speed measurement by time-recording method of the front-stage measurement circuit is: The speed expression of the post-stage measurement circuit in time method is: When the error of the time method and the distance method of the front-stage measurement circuit are the same, the solution is The time measurement frequency of the current level measurement circuit is equal to the minimum frequency f required by the system. s When The motor speed is set to sp m =f s / n e ; The method for selecting the final output speed value is: When the system is running, when the speed is greater than That is, the microcontroller detects that the conditions are met or When the speed meets the requirement, the single chip microcomputer uses the front stage measurement circuit to record the speed expression of the distance method to output the speed; when the speed meets the requirement, the single chip microcomputer uses the front stage measurement circuit to record the speed expression ... That is, the microcontroller detects that the conditions are met or and n2≤f c / f s or n3≤f c / (f s +sp m *n e ), the single chip microcomputer uses the front stage measurement circuit to record the time method speed expression to output the speed; when the speed is less than f s / n e When the MCU detects that the condition n2>f is satisfied c / f s or n3>f c / (f s +sp m *n e ), the single chip computer uses the subsequent measurement circuit to record the speed expression of the time method to output the speed.

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