A machine tool spindle impact protection system

Abstract

This invention discloses a machine tool spindle impact protection system, including a vibration sensor, a low-pass filter, a self-learning data judgment module, and an industrial controller. The vibration sensor is installed near the spindle and connected to the low-pass filter, which in turn is connected to the self-learning data judgment module. The industrial controller is also connected to the self-learning data judgment module. This invention belongs to the technical field of manufacturing and CNC machining systems. Specifically, it provides a system that uses a vibration sensor with a differentiator and comparator. By learning vibration data during normal operation, it obtains a DAC output level, which is compared with the output of the differentiator and the signal is transmitted to a PLC or contactor for power-off. The differentiator can predict signal abrupt changes in advance, thereby achieving spindle impact protection within microseconds, further reducing spindle damage and facilitating cost-effective machine tool spindle impact protection.

Description

Technical Field

[0001] This invention belongs to the technical field of manufacturing and CNC machining systems, specifically referring to a machine tool spindle impact protection system. Background Technology

[0002] The spindle is the most crucial component of a machine tool. Wear or impact from cutting tools will severely affect machining accuracy, especially for electric spindles, where accuracy can drop by more than tenfold. Therefore, knowing how to safely cut off the power supply within a safe timeframe when a spindle is impacted will minimize damage to the spindle and ensure machining accuracy.

[0003] Existing technology involves the main controller acquiring data from a three-axis accelerometer mounted on the spindle to obtain the spectrum during normal spindle operation, calculating and saving the peak value. An upper limit is set at 10 times the peak value during operation. When the acquired and processed data exceeds this upper limit, the main controller sends an I / O signal to the machine tool PLC, which then cuts off the main power supply.

[0004] In the aforementioned techniques, the signal needs to be low-pass filtered first, and then the acquired data is processed, such as by Fast Fourier Transform or Wavelet Transform. Typically, the cutoff frequency of the low-pass filter is chosen to match the spindle's operating frequency. Due to the amplitude-frequency characteristics of the low-pass filter, the signal amplitude will attenuate by -3dB after passing through it, and a significant delay will occur at the cutoff frequency. The selection of the low-pass filter cutoff frequency affects the signal rise time, creating a trade-off: it's impossible to obtain both a clean signal and a fast response time simultaneously. Furthermore, data processing also takes time. If the processor performance is low, it will take a long time, resulting in the inability to send a power-off protection signal in time, thus failing to protect the spindle. If the processor performance is high, the processor's price will increase the overall cost, and high-sensitivity triaxial accelerometers are expensive and not conducive to mass production. Summary of the Invention

[0005] To address the above issues and overcome the shortcomings of existing technologies, this invention provides a protection system that uses a common mechanical vibration sensor with a differentiator and comparator. By learning vibration data during normal operation, a DAC output level is obtained and compared with the output of the differentiator. If the level exceeds the DAC output, the signal is directly transmitted to the PLC or contactor to cut off power. The differentiator can predict signal abrupt changes in advance, thereby achieving spindle impact protection within microseconds, further reducing spindle damage and providing a cost-effective machine tool spindle impact protection system.

[0006] The technical solution adopted by the present invention is as follows: The present invention provides a machine tool spindle impact protection system, including a vibration sensor, a low-pass filter, a self-learning data judgment module, and an industrial controller. The vibration sensor is installed near the spindle, the output end of the vibration sensor is connected to the input end of the low-pass filter, the output end of the low-pass filter is connected to the input end of the self-learning data judgment module, and the industrial controller is connected to the output end of the self-learning data judgment module.

[0007] As a further explanation, the self-learning data judgment module includes an AD acquisition unit, a main controller, a DA converter, a differentiator, and a comparator. The output shaft of the vibration sensor is connected to the AD acquisition unit via the low-pass filter. The output of the AD acquisition unit is connected to the input of the main controller. The output of the main controller is connected to the input of the DA converter. The output of the low-pass filter is connected to the input of the differentiator. The outputs of the differentiator and the DA converter are both connected to the comparator. The industrial controller is connected to the output of the comparator.

[0008] Preferably, the output signal of the differentiator is divided into two paths, one of which enters the positive input terminal of the comparator, and the other of which enters the AD acquisition unit.

[0009] Furthermore, the main controller is equipped with a storage unit. The main controller reads data from the AD acquisition unit to learn relevant data during normal spindle operation and saves the relevant data to the storage unit.

[0010] In a preferred embodiment, the main controller outputs the minimum upper limit level to the negative input of the comparator via a DA converter.

[0011] In a preferred embodiment, the industrial controller is a PLC or a contactor.

[0012] As a further explanation, the output of the comparator is connected to a trigger, and the input signal of the trigger can directly drive the contactor to disconnect the power supply or be input to the PLC controller to perform a power-off operation.

[0013] Furthermore, the vibration sensor output signal is an analog signal. The analog signal is filtered by a low-pass filter to remove other high-frequency components and retain the required frequency components. The cutoff frequency of the low-pass filter is set to be more than 30 times the frequency of the main shaft vibration.

[0014] The beneficial effects of this invention using the above structure are as follows: This solution provides a machine tool spindle impact protection system, solving the problems of slow response speed and high cost of existing products, and improving the real-time performance and speed of spindle protection. By using a common mechanical vibration sensor, the protection system incorporates a differentiator and comparator. It learns vibration data during normal operation to obtain a DAC output level, which is compared with the output of the differentiator. If the level exceeds the DAC output, the signal is directly transmitted to the PLC or contactor to cut off power. The differentiator can predict signal abrupt changes in advance, thus achieving spindle impact protection within microseconds. Using a common piezoelectric vibration sensor and a low-speed main control chip eliminates the need for high-speed data processing, significantly reducing costs. It can detect impacts in advance, further reducing spindle damage and protecting original accuracy. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall principle of the machine tool spindle impact protection system provided in this solution;

[0016] Figure 2 This is a schematic diagram of the differentiator in this scheme;

[0017] Figure 3 This is a schematic diagram showing the composition of the comparator and flip-flops in this scheme;

[0018] Figure 4 A schematic diagram illustrating how a trigger input signal drives the power-off operation of an industrial controller.

[0019] Figure 5 The response waveform diagram provided for this solution.

[0020] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] like Figure 1-5As shown, the present invention discloses a machine tool spindle impact protection system, comprising a vibration sensor, a low-pass filter, a self-learning data judgment module, and an industrial controller. The vibration sensor is installed near the spindle, and the output end of the vibration sensor is connected to the input end of the low-pass filter. The output end of the low-pass filter is connected to the input end of the self-learning data judgment module, and the industrial controller is connected to the output end of the self-learning data judgment module.

[0023] As a further explanation, the self-learning data judgment module includes an AD acquisition unit, a main controller, a DA converter, a differentiator, and a comparator. The output shaft of the vibration sensor is connected to the AD acquisition unit via a low-pass filter. The output of the AD acquisition unit is connected to the input of the main controller. The output of the main controller is connected to the input of the DA converter. The output of the low-pass filter is connected to the input of the differentiator. The outputs of the differentiator and the DA converter are both connected to the comparator. The industrial controller is connected to the output of the comparator. The industrial controller is either a PLC or a contactor.

[0024] The principle behind this solution is as follows:

[0025] In this solution, after the spindle starts normally and stabilizes, it will generate a fixed frequency. The vibration sensor collects the vibration signal of the spindle. Unlike the digital signal output of the triaxial accelerometer, the vibration sensor output signal provided in this solution is an analog signal. The analog signal is filtered by a low-pass filter to remove other high-frequency components and retain the required frequency components. The cutoff frequency of the low-pass filter is set to be more than 30 times the vibration frequency of the spindle. According to the amplitude-frequency characteristics, the output signal amplitude at the spindle's operating frequency is almost unaffected, and the delay will be much lower than the delay at the cutoff frequency.

[0026] like Figure 2 As shown, Figure 2 The provided differentiator consists of operational amplifier A1, capacitor C1, resistors R1 and R2, and the output signal of the low-pass filter is the input signal V1 of the differentiator.

[0027] In this calculation, the resistance value of R2 is chosen to be a standard large resistor (such as 1MΩ), so that the value of capacitor C1 will be controlled within a reasonable range. The value of C1 is obtained by the formula C1=3.5 / (2×π×R2×f), where f is the main shaft vibration frequency. The value of R1 is obtained by the formula R1=1 / (3.5×2×π×C1×f).

[0028] The output signal V2 of the differentiator is split into two paths. One path enters the positive input of the comparator, and the other path enters the AD acquisition unit. The main controller reads the data from the AD acquisition unit to learn relevant data during normal spindle operation, saves the relevant data to the storage unit, and determines the minimum upper limit value when the spindle experiences an impact through experiments. The main controller outputs the minimum upper limit value level V3 to the negative input of the comparator through the DA converter.

[0029] like Figure 3 As shown, the output of the comparator is connected to a flip-flop. The output V4 of comparator A2 is the input of the flip-flop, and the output of the flip-flop is V5. The function of the flip-flop is to output a high level signal V5 and maintain a high level when the rising edge of the input signal V4 arrives.

[0030] During normal operation, the negative input V2 of the comparator is much lower than the positive input V3, and the comparator output V4 is low. The flip-flop remains low. When the spindle is struck, the positive input V2 will exceed the negative input V3, and the comparator output signal V4 will be high. At this time, due to the rising edge of V4, the flip-flop output V5 becomes high and remains high.

[0031] like Figure 4 As shown, the input signal of the trigger can directly drive the contactor to disconnect the power supply or be input to the PLC controller so that the PLC can perform the power-off operation.

[0032] like Figure 5 As shown, this solution uses a differentiator to detect impacts in advance. During normal operation, the spindle's vibration period is T. When an impact occurs at time t2, the vibration signal at point P2 exceeds the upper limit. Existing technology requires at least one cycle T of data acquisition before processing and determining whether power should be cut off. However, with this solution, since the differentiator's output is the slope of a curve, when the slope exceeds the upper limit at point P1, the comparator outputs a high level, triggering a high-level output to disconnect the power. The time at point P1 is t1, which is much shorter than T, and the comparator's response time is only a few microseconds, negligible. Therefore, this solution significantly shortens the detection time, protects the spindle promptly, minimizes damage, and ensures that the machine tool's accuracy does not decrease significantly after an impact.

[0033] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0034] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0035] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A machine tool spindle impact protection system, characterized in that: The system includes a vibration sensor, a low-pass filter, a self-learning data judgment module, and an industrial controller. The vibration sensor is installed near the spindle, and its output is connected to the input of the low-pass filter. The output of the low-pass filter is connected to the input of the self-learning data judgment module, and the industrial controller is connected to the output of the self-learning data judgment module. The self-learning data judgment module includes an AD acquisition unit, a main controller, a DA converter, a differentiator, and a comparator. The output shaft of the vibration sensor is connected to the AD acquisition unit via the low-pass filter. The output of the AD acquisition unit is connected to the input of the main controller. The output of the main controller is connected to the input of the DA converter. The output of the low-pass filter is connected to the input of the differentiator. The outputs of the differentiator and the DA converter are both connected to the comparator. The industrial controller is connected to the output of the comparator. The output signal of the differentiator is divided into two paths. One output signal enters the positive input terminal of the comparator, and the other output signal enters the AD acquisition unit.

2. The machine tool spindle impact protection system according to claim 1, characterized in that: The main controller has an internal storage unit. The main controller reads data from the AD acquisition unit to learn relevant data during normal spindle operation and saves the relevant data to the storage unit.

3. The machine tool spindle impact protection system according to claim 2, characterized in that: The main controller outputs the minimum upper limit level to the negative input of the comparator via a DA converter.

4. The machine tool spindle impact protection system according to claim 1, characterized in that: The industrial controller is a PLC or a contactor.

5. The machine tool spindle impact protection system according to claim 1, characterized in that: The output of the comparator is connected to a trigger. The input signal of the trigger can directly drive the contactor to disconnect the power supply or be input to the PLC controller to perform a power-off operation.

6. The machine tool spindle impact protection system according to claim 1, characterized in that: The vibration sensor outputs an analog signal, which is filtered by a low-pass filter to remove other high-frequency components and retain the desired frequency components.

7. The machine tool spindle impact protection system according to claim 1, characterized in that: The cutoff frequency of the low-pass filter is set to be at least 30 times the frequency of the spindle vibration.

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