A spindle speed monitoring system

Abstract

Provided is an electric spindle speed monitoring system, belonging to the field of mechanical processing. The electric spindle speed monitoring system comprises: an electric spindle, a spindle supporting numerical control system, a signal preprocessing circuit board, an acquisition module and a host computer; the electric spindle, the spindle supporting numerical control system and the signal preprocessing circuit board are communicatively connected, the signal preprocessing circuit board is electrically connected to the acquisition module, and the acquisition module is communicatively connected to the host computer. The present invention adopts an encoder three-way line and a high-resolution acquisition system to lead the signal of the electric spindle encoder all the way to the acquisition system of the encoder signal preprocessing module for acquisition, and performs signal processing by the host computer to realize online real-time monitoring of the speed of the spindle cutting state at a smaller time scale, and finds a stable speed for processing through real-time speed monitoring, thereby improving the machining accuracy of the machine tool and the consistency of batch workpieces.

Description

Technical Field

[0001] The invention relates to the field of mechanical processing, and in particular to an electric spindle speed monitoring system. Background Art

[0002] During the actual machining operation of the electric spindle, the fluctuation of the speed will have a great impact on the quality and machining efficiency of the workpiece. During the high-precision machining process, the fluctuation or deviation of the electric spindle speed will cause the surface of the part to be uneven or the circular surface to be asymmetric or the size of the hole to deviate from the design parameters. In the current situation, there are some deviations or errors in the speed measurement. The measurement deviation or error of the speed also causes errors in the control strategy of the machine tool or CNC, which further affects the machining accuracy. Therefore, there is a need to accurately measure and control the electric spindle speed. Summary of the invention

[0003] The purpose of the present invention is to provide an electric spindle speed monitoring system to solve the problem of improving the speed monitoring and control of the electric spindle on a smaller time scale.

[0004] An electric spindle speed monitoring system, characterized in that it comprises: an electric spindle, a spindle matching numerical control system, an encoder three-way cable, a signal preprocessing circuit board, an acquisition module and a host computer;

[0005] The electric spindle, the spindle supporting numerical control system and the signal preprocessing circuit board are communicatively connected, the signal preprocessing circuit board is electrically connected to the acquisition module, and the acquisition module is communicatively connected to the host computer.

[0006] Optionally, the electric spindle is controlled to rotate at a preset speed through a CNC machining parameter panel of a CNC system supporting the spindle.

[0007] Optionally, the electric spindle, the spindle-matching numerical control system and the signal preprocessing circuit board are communicatively connected via an encoder three-way cable. The encoder three-way cable feeds back the encoder signal of the electric spindle to the spindle-matching numerical control system and transmits the speed signal to the signal preprocessing circuit board at the same time.

[0008] Optionally, the spindle-matching numerical control system controls and adjusts the rotation speed of the electric spindle according to the feedback signal of the encoder.

[0009] Optionally, the encoder of the electric spindle outputs sine and cosine signals when rotating, and the sine and cosine signals are sequentially input into the filter protection circuit, differential amplifier and zero-crossing comparator of the signal preprocessing circuit board through the encoder three-way cable to generate a 0-5V square wave signal.

[0010] Optionally, the square wave signal is connected to an acquisition module to sample the converted square wave signal, and the sampled signal data is connected to a host computer.

[0011] Optionally, the sampling rate of the acquisition module is greater than or equal to (N*n) / 20-(N*n) / 12, the maximum measured speed is nr / min, and the number of teeth of the electric spindle encoder is N.

[0012] Optionally, the sampling number of the acquisition module is k points per second, N1 and N2 are the sampling point count values ​​of the rising edges of two adjacent square waves, N1 is the sampling point count value corresponding to the previous square wave, and N2 is the sampling point count value corresponding to the next square wave; the rotation speed accurately measured and calculated at a small time scale of the rising edges of two adjacent square waves is: k*60 / ((N2-N1)*N).

[0013] Optionally, the rotation speed accurately measured and calculated by the host computer on a small time scale is fed back to the spindle's supporting CNC system to form a closed-loop feedback control of the electric spindle.

[0014] Optionally, the electric spindle is a servo motor.

[0015] Beneficial technical effects:

[0016] It can realize the speed monitoring of the electric spindle on a smaller time scale and the design of the external speed monitoring system of the electric spindle. By analyzing the relationship between the speed characteristics of the electric spindle and the machining accuracy and the analysis of the abnormal situation of the electric spindle, it can timely discover and locate the fault and improve the machining accuracy and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0018] Figure 1 The principle block diagram of measuring rotation speed by the period measurement method is shown.

[0019] Figure 2 A schematic diagram of error generation in the frequency measurement method and the period measurement method is shown.

[0020] Figure 3 Structural diagram of the electric spindle speed monitoring system according to an embodiment of the present invention.

[0021] Figure 4 Schematic diagram of the electric spindle speed monitoring system according to an embodiment of the present invention.

[0022] Figure 5 Flowchart of data processing according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0024] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0025] Embodiment 1

[0026] like Figure 1 The frequency measurement method and the period measurement method are often used to measure the rotational speed. The frequency measurement method uses the pulse to be measured to fill the standard time, and the counter accumulates the number of pulses to be measured within the same period of a standard clock pulse signal, thereby obtaining the rotational speed to be measured; the period measurement method uses the standard clock pulse to fill the pulse to be measured, and the counter accumulates the number of standard clock pulses Na within a period Ta of the pulse signal to be measured, thereby obtaining the rotational speed to be measured n1. The principle of measuring the rotational speed by the cycle measurement method is as follows: the crystal oscillator pulse signal after amplification and shaping is transmitted to the input end of the main gate, so that the pulse signal to be measured output from the speed sensor enters the control gate. When the first pulse signal to be measured enters the control gate, the bistable trigger in the gate is flipped, thereby opening the main gate and allowing the crystal oscillator pulse to pass through. When the second pulse to be measured enters the control gate, the bistable trigger in the gate is flipped again, closing the main gate and not allowing the crystal oscillator pulse to pass through. The interval between the two pulse signals to be measured is the pulse signal period Ta to be measured. The counter accumulates the number of crystal oscillator pulses Na within Ta. The speed n1 to be measured is n1=60 / (n2*Ta), and n2 is the number of pulses generated when the measured shaft rotates one circle.

[0027] like Figure 2The error of measuring the rotation speed by the frequency measurement method and the period measurement method is composed of three parts, namely the error of the rotation speed sensor, the frequency stability error of the crystal oscillator and the sampling error caused by the phase of the measured pulse signal being out of sync with the starting time of the control gate output signal. The error of the rotation speed sensor under normal working conditions is very small and can be ignored. If it is caused by power supply fluctuations, aging of photosensitive elements, insufficient light source, improper gap or too low measurement speed, it is not regarded as a normal measurement error, and the error caused by the unstable crystal oscillation frequency is very small in magnitude and can be ignored. Therefore, the main reason for the measurement error is the randomness of the phase when the starting time t0 of the time base signal t1 output by the control gate falls on the measured pulse wave, such as Figure 2 Similarly, during the t1 time, the number of pulses entering may be one more or one less, so this error is called ±1 digital error.

[0028] The error of the frequency measurement method is expressed as:

[0029]

[0030] The error of the circumference measurement method is expressed as:

[0031]

[0032] Tz represents the gate time, Tx represents the measured period, fx represents the measured frequency, f represents the clock frequency, Δf x represents the absolute error of fx, ΔT x Indicates the Tx absolute error.

[0033] Where Nx is the number of pulses entering the counter within time t1.

[0034] The frequency error caused by ±1 pulse is Δf x =1 / t1;

[0035] The relative error is δ = Δf x / f x =1 / (f x t1),

[0036] because n1 is the rotation speed, and Z1 is the number of gratings or teeth on the rotating disk.

[0037] The relative error is

[0038] (1) shows that the relative error of speed measurement is affected by the combined influence of n1, Z1 and t1, and is given by Figure 2As shown in the figure, due to the randomness of the phase when the starting time t0 of the time base signal t1 output by the control gate falls on the measured pulse wave, the number of incoming pulses may be one more or one less. This ±1 digital error causes deviation in the measurement of the rotational speed during part finishing, thereby affecting the control accuracy. In addition, since traditional measurements measure the number of pulses within the time base signal t1, it lacks the ability to track and monitor the fluctuations of high rotational speed on a smaller time scale and cannot truly reflect the fluctuations of high rotational speed.

[0039] See also Figure 3-5 , electric spindle 1, spindle supporting CNC system 2, encoder three-way cable 3, signal preprocessing circuit board 4, high-resolution acquisition module 5, host computer 6.

[0040] The encoder of the electric spindle can output sine and cosine signals.

[0041] The signal preprocessing circuit board 4 has a filtering protection circuit, a differential amplifier and a zero-crossing comparator.

[0042] The high-resolution acquisition module 5 is required to be able to collect 0-10V voltage signals. The maximum measurement speed is nr / min, the number of teeth of the electric spindle encoder is N, and the sampling rate of the acquisition module is greater than or equal to 3*(N*n) / 60-5*(N*n) / 60 to meet high-precision data acquisition. 3*(N*n) / 60-5*(N*n) / 60 is the range of (N*n) / 20-(N*n) / 12.

[0043] The electric spindle 1, the spindle supporting numerical control system 2 and the signal preprocessing circuit board 4 are connected through the encoder three-way cable 3, and the electric spindle 1 is controlled to rotate at a certain speed through the numerical control processing parameter panel of the spindle supporting numerical control system 2. On the one hand, the encoder three-way cable 3 can feed back the encoder signal of the electric spindle 1 to the spindle supporting numerical control system 2, so that the spindle supporting numerical control system 2 can control and adjust the speed of the electric spindle according to the feedback signal of the encoder; on the other hand, the encoder three-way cable 3 outputs the speed information signal in parallel and transmits it to the signal preprocessing circuit board 4. The encoder of the electric spindle 1 outputs sine and cosine signals when rotating. The sine and cosine signals are input into the filtering protection circuit of the signal preprocessing circuit board 4 through the encoder three-way cable 3. In order to prevent the subsequent amplification circuit and the like from affecting the signal transmitted from the electric spindle 1 to the spindle supporting numerical control system 2, after passing through the filtering protection circuit of the signal preprocessing circuit board 4, the differential amplifier of the signal preprocessing circuit board 4 is output to amplify the sine and cosine signals, and then the zero-crossing comparator of the signal preprocessing circuit board 4 is output to generate a 0-5V square wave signal, and one cycle of the square wave signal is one cycle of the sine signal; then the square wave signal is connected to the high-resolution acquisition module 5 to sample the converted square wave signal, and the sampled signal data is connected to the host computer 6, and the sampled square wave signal is software filtered and The speed calculation can realize the accurate monitoring of the speed of the electric spindle 1 during the rotation process. When the electric spindle 1 rotates, the sine wave signal fed back by the encoder signal is transmitted to the signal preprocessing circuit board 4, the high-resolution acquisition module 5 and the host computer 6 to be converted into a square wave signal. The time interval between the adjacent rising edges of the square wave signal is small. This time interval is related to the number of teeth and the speed of the encoder and can be used to calculate the speed, thereby realizing the accurate monitoring of the speed of the electric spindle 1 at a smaller scale. The number of teeth of the encoder is N, and the speed monitoring system realizes the calculation of the speed once. The time is 1 / N of the time of one rotation of the electric spindle. The speed is calculated according to the time interval between the adjacent rising edges of the square wave signal. The time interval between the adjacent rising edges of the square wave signal is ts. The sampling number of the acquisition module is k points (k points are sampled per second), then the speed is 60 / (t*N)r / min, where t can be calculated as (N2-N1) / ks according to the sampling number, N1 and N2 are the sampling point count values ​​of the two adjacent square wave rising edges, N1 is the sampling point count value corresponding to the previous square wave, and N2 is the sampling point count value corresponding to the next square wave;

[0044] Therefore, the rotation speed calculated by accurate measurement on a small time scale is:

[0045] k*60 / ((N2-N1)*N)r / min, (2)

[0046] The above formula (2) calculates the rotational speed by using the sampling point count values ​​N1 and N2 of the rising edges of two adjacent square waves. On the one hand, it eliminates the influence of the ±1 pulse digital error; on the other hand, it eliminates the influence of the time base signal t1, because the rotational speed is not affected by the length or change of the time base signal t1 at this time; on the third hand, the error is not affected by the rotational speed, because the calculation of the rotational speed is independent of the rotational speed of the electric spindle 1 at this time; on the fourth hand, the rotational speed measurement is more accurate by using the sampling point count values ​​N1 and N2 of the rising edges of two adjacent square waves. The time interval between the two adjacent square wave rising edges minimizes the rotational speed measurement, so that the rotational speed and rotational speed change can be measured accurately on the minimum time scale.

[0047] The rotation speed calculated in the above formula (2) is displayed in real time on the host computer 6.

[0048] The electric spindle 1, the spindle-matching numerical control system 2 and the signal preprocessing circuit board 4 are communicatively connected via the encoder three-way cable 3. The encoder three-way cable 3 enables the speed signal of the electric spindle 1 to be synchronously transmitted to the spindle-matching numerical control system 2 and the signal preprocessing circuit board 4, thereby reducing the asynchrony of the speed signal transmission, so that the spindle-matching numerical control system 2 and the signal preprocessing circuit board 4 can process, control and respond to the speed signal without delay; the encoder three-way cable 3 reduces the use of cables and saves cable costs.

[0049] Embodiment 2

[0050] In addition to the speed monitoring of the electric spindle on a smaller scale, the electric spindle can also be replaced with a servo motor, and the servo motor speed can be measured based on the sine and cosine waves output by the servo motor encoder. The electric spindle can also be replaced with an asynchronous motor or a synchronous motor.

[0051] Embodiment 3

[0052] The rotation speed accurately measured and calculated by the host computer 6 on a small time scale is fed back to the spindle supporting numerical control system 2 to form a closed-loop feedback control of the electric spindle 1.

[0053] Embodiment 4

[0054] The upper computer 6 performs signal processing to realize online real-time monitoring of the spindle speed in a smaller time scale of the cutting state. When the speed does not change for 2m+1 times in a row, m is a positive integer, and the upper computer transmits the speed unchanged signal to the spindle supporting CNC system 2. The spindle supporting CNC system 2 processes at a stable speed, thereby improving the machining accuracy of the machine tool and the consistency of batch workpieces.

[0055] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in terms of function in the above description. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0056] It should be noted that the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0057] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An electric spindle speed monitoring system, characterized in that: include: An electric spindle (1), a spindle-matching numerical control system (2), a signal preprocessing circuit board (4), an acquisition module (5), and a host computer (6); The electric spindle (1), the spindle supporting numerical control system (2) and the signal preprocessing circuit board (4) are communicatively connected, the signal preprocessing circuit board (4) is electrically connected to the acquisition module (5), and the acquisition module (5) is communicatively connected to the host computer (6); The encoder of the electric spindle (1) outputs sine and cosine signals when rotating, and the sine and cosine signals are sequentially input into the filter protection circuit, the differential amplifier and the zero-crossing comparator of the signal preprocessing circuit board (4) through the encoder three-way cable (3); The square wave signal is connected to the acquisition module (5) to sample the converted square wave signal, and the sampled signal data is connected to the host computer (6); The sampling rate of the acquisition module is greater than or equal to (N*n) / 20-(N*n) / 12, the maximum speed to be measured is nr / min, and the number of teeth of the electric spindle encoder is N; The sampling number of the acquisition module is k points per second. N1 and N2 are the sampling point count values ​​of the rising edges of two adjacent square waves. N1 is the sampling point count value corresponding to the previous square wave, and N2 is the sampling point count value corresponding to the next square wave. The rotation speed accurately measured and calculated at a small time scale of the rising edges of two adjacent square waves is: k*60 / ((N2-N1)*N).

2. The electric spindle speed monitoring system according to claim 1, characterized in that: The electric spindle (1) is controlled to rotate at a preset speed through a CNC machining parameter panel of a CNC system (2) supporting the spindle.

3. The electric spindle speed monitoring system according to claim 1, characterized in that: The electric spindle (1), the spindle-matching numerical control system (2), and the signal preprocessing circuit board (4) are communicatively connected via an encoder three-way cable (3); the encoder three-way cable (3) feeds back the encoder signal of the electric spindle (1) to the spindle-matching numerical control system (2) and transmits the speed signal to the signal preprocessing circuit board (4).

4. The electric spindle speed monitoring system according to claim 1, characterized in that: The spindle-matching numerical control system (2) controls and adjusts the rotation speed of the electric spindle (1) according to the feedback signal of the encoder.

5. The electric spindle speed monitoring system according to claim 1, characterized in that: The sine and cosine signals are sequentially input into the filter protection circuit, the differential amplifier and the zero-crossing comparator of the signal preprocessing circuit board (4) through the encoder three-way cable (3) to generate a 0-5V square wave signal.

6. The electric spindle speed monitoring system according to claim 1, characterized in that: The rotation speed accurately measured and calculated by the host computer (6) at a small time scale is fed back to the spindle supporting numerical control system (2), thereby forming a closed-loop feedback control of the electric spindle (1).

7. The electric spindle speed monitoring system according to claim 1, characterized in that: The electric spindle (1) is a servo motor.

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