Method for monitoring maintenance and lubricating of toggle bearing of injection molding machine
Patent Information
- Authority / Receiving Office
- TW · TW
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2020-10-07
- Publication Date
- 2022-04-16
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a lubrication status monitoring system and method for a crank bearing of a toggle mechanism in a plastic injection molding machine. [Previous Technology]
[0002] Plastics are one of the most widely used materials in the world. Today, the use of plastic parts dominates in end-user industries such as automotive, packaging, home appliances, and medical. A large portion of these plastic parts are produced using plastic injection molding technology. The popularity of plastic injection molding stems from its ability to produce large quantities of plastic parts with varying geometric complexities in a short time, typically without requiring secondary processing. Plastic injection molding is defined as the process of injecting molten plastic material into a mold, followed by cooling and solidification. By the end of 2025, the global plastic injection molding market is estimated to exceed US$470 billion.
[0003] An injection molding machine consists of three main parts: an injection unit, a mold assembly unit, and a clamping unit. In the plastic injection molding industry, two types of clamping units are commonly used: plunger type and toggle type. The plunger type is used for producing precision parts, while the toggle type is used for high-speed plastic injection molding. The toggle type is generally more energy-efficient than the plunger type. The plastic injection molding process begins when the mold is closed via the toggle clamping unit. After the mold is closed, molten plastic material is injected and fills the mold cavity. The plastic material then undergoes a cooling process, resulting in the formation of a solid part. In the final step, the toggle clamping unit opens the mold, making the finished product easy to eject. Considering the nature of the injection molding process, it is unavoidable that the toggle clamping unit will undergo multiple repeated opening and closing cycles during production. The lubrication condition of the bearings (commonly known as crank bearings) of the toggle clamping unit deteriorates with the increase in the number of cycles, and the repeated mold opening and closing process gradually degrades the lubricating oil, leading to poor lubrication and increased wear. To date, numerous studies have focused on improving the oils used in injection molding machines and attempting to improve the lubrication system of the toggle clamping unit. However, there are almost no systems or methods for real-time monitoring of the lubrication status of the crankshaft bearing in the toggle clamping unit. Therefore, to avoid lubrication failure in the toggle clamping unit, the current practice is for machine operators to rely on their own operating experience or simple empirical formulas to estimate the lubrication cycle for re-lubricating the crankshaft bearing. This method lacks objective scientific basis and often wastes lubricant due to premature lubrication.
[0004] Although there is a patent application No. I644782, "Method for Lubrication Detection and Application of Machine Linkage Mechanism," published on December 21, 2018 (Republic of China Year 107), it mainly discloses that: the machine includes a mold and a mold locking device; the mold locking device includes a linkage mechanism and a mold locking motor, the linkage mechanism is displaced by the mold locking motor to drive the mold to move between an open position and a closed position. First, a preset torque value is set, and the output torque value when the mold locking motor is actuated is detected; then, it is determined whether the measured output torque value is greater than the preset torque value. When the output torque value is greater than the preset torque value, a warning message is generated, and lubrication is applied to the linkage mechanism. In this way, lubrication is provided in a timely manner according to the torque change of the mold locking motor, so as to improve the machine's operating efficiency and reduce lubrication costs.
[0005] The aforementioned patent case mainly monitors the torque value before lubricating the linkage mechanism. However, it does not lubricate the crank bearing of the toggle locking unit, and therefore is completely different from the technical features and effects achieved by the present invention.
[0006] There is also a utility model patent application No. M592816, "Predictive Maintenance System for Moving Slide Plate of Injection Molding Machine", which was announced on April 1, 2020. The main disclosure is that it includes an injection molding machine and a warning unit. The injection molding machine has a base and a movable mold wall. At least one slide plate is fixed at the bottom of the movable mold wall. The movable mold wall sits on the base with the slide plate. The warning unit is located in the injection molding machine. The warning unit is used to obtain a distance measurement value. The distance measurement value will change with the wear of the slide plate. Therefore, when the wear of the slide plate reaches the allowable amount, the distance measurement value will also reach a predetermined value. Then the warning unit will issue a warning to remind the technician to maintain the slide plate.
[0007] The previous patent application was also not for lubricating the crank bearing of the toggle locking unit, and therefore it is completely different from the technical features and effects achieved by the present invention. [Summary of the Invention]
[0008] Therefore, in view of the aforementioned disadvantages of the conventional hand bearings in injection molding machines in terms of maintenance and lubrication, the present invention provides a system for monitoring the maintenance and lubrication of hand bearings in injection molding machines, comprising: at least one vibration sensor, installed on a hand bearing of an injection molding machine to detect vibration changes of the hand bearing, the vibration sensor outputting a vibration signal based on the detected vibration changes; a smart box connected to the vibration sensor to receive the vibration signal, convert the vibration signal into a digital vibration signal, and then output the digital vibration signal; a control unit connected to the smart box to receive the digital vibration signal, establish a lubrication failure index based on it, and output a lubrication command when the lubrication failure index changes too much; and an oiling unit connected to the control unit to receive the lubrication command and perform an oiling action on the hand bearing.
[0009] The above-mentioned vibration sensor is an accelerometer.
[0010] An external display device is further provided to display the lubrication failure indicator.
[0011] The present invention is also a method for monitoring the maintenance and lubrication of a crankshaft bearing in an injection molding machine, comprising the following steps: a vibration sensor detects the vibration change of a crankshaft bearing in an injection molding machine and continuously outputs a vibration signal; a smart box receives the vibration signal and converts it into a digital vibration signal output; a control unit receives the digital vibration signal and establishes a lubrication failure index based on the vibration change, and outputs a lubrication command when the change of the lubrication failure index is too large; an oiling unit receives the lubrication command and applies an oiling action to the crankshaft bearing.
[0012] The vibration sensor is installed at the location of the aforementioned crank bearing, and the vibration sensor is used to detect the vibration changes of the crank bearing at any time.
[0013] After storing the vibration signal, the above-mentioned smart set-top box uses various time-frequency analysis methods to process the vibration signal, performs filtering, contour data extraction, and simple data analysis of Fourier transform, and outputs the vibration signal after converting it into a digital vibration signal.
[0014] After receiving the digital vibration signal, the control unit uses shock response spectrum analysis to analyze the difference between the vibration signals captured in each mold switching cycle, finds the signal difference of the shock response spectrum after the previous oiling, and analyzes the signal regularity of the shock response spectrum before and after oiling. This is used to establish the lubrication failure index that requires re-oiling. When the change of the lubrication failure index is too large, the control unit will output the lubrication command to apply the oiling action to the crank bearing, and then perform the acquisition of the vibration signal for the next mold switching cycle. When the change of the lubrication failure index is not too large, the acquisition of the vibration signal for the next mold switching cycle will proceed directly.
[0015] The changes in the above-mentioned lubrication failure indicators are displayed by an external display device to facilitate direct visual judgment and serve as the basis for manual lubrication.
[0016] The determination of whether the above-mentioned lubrication failure index changes too much includes the following steps: a. Extracting the shock response spectrum index of the vibration signal during the switching process; b. Starting from the Nth switching cycle after the start, estimating the instantaneous rate of change at the Nth point by the shock response spectrum values of the previous N-1 switching cycles, where N is a positive integer; c. Repeating step b for all subsequent switching cycles; d. Starting from the Mth switching cycle, using the Grubbs test to perform outlier testing to determine whether the z-value of the instantaneous rate of change exceeds the 95% confidence interval of the distribution. If the z-value is greater than the 95% confidence interval, it is determined that the change of the lubrication failure index is too much and lubrication is required; if it is less than the 95% confidence interval, it is determined that the change of the lubrication failure index is not too much and lubrication is not required.
[0017] The above N=8, M=71.
[0018] The above-mentioned technical features have the following advantages:
[0019] 1. During the opening and closing movement of the toggle clamping unit of the injection molding machine, the vibration signal generated by the crank bearing is captured to establish a lubrication failure index, thereby setting the optimal time point for maintenance and lubrication. The monitoring system and method can be implemented on any type of injection molding machine with a toggle clamping unit.
[0020] 2. The vibration signal captured by the crank bearing of the toggle clamping unit is analyzed. Various time-frequency analysis methods are used to process the vibration signal. Then, the impact response spectrum method is used to find the lubrication failure index in the captured vibration signal that can determine the optimal time for lubrication of the crank bearing.
[0021] 3. The lubrication cycle is based on theory and does not need to rely on the operator's not necessarily correct operating experience to determine the lubrication cycle, thus it has excellent accuracy.
[0022] 4. The lubrication failure index of each injection molding machine will change with each mold opening and closing, machine depreciation, and the different sizes, weights, and volumes of the injection mold. Existing conventional technology cannot fully reflect and match this. The present invention can adjust the appropriate lubrication cycle according to the changes in the lubrication failure index to achieve the optimal lubrication prediction and maintenance function.
Implementation Method
[0033] Please refer to Figures 1 and 2. The first embodiment of the present invention is a system for monitoring the maintenance and lubrication of the crank bearing of an injection molding machine, comprising: a vibration sensor 1, a smart machine housing 2, a control unit 3, and an oiling unit 4, wherein:
[0034] At least one vibration sensor 1 is available for mounting on a toggle clamping unit G1 of an injection molding machine G, preferably mounted on a crank bearing C2 of the toggle clamping unit G1. By detecting vibration changes in the toggle clamping unit G1 caused by wear of the crank bearing G2, the vibration sensor 1 outputs a vibration signal based on the detected vibration changes. The vibration sensor 1 is an accelerometer.
[0035] The Smart Machine Box 2 is connected to the vibration sensor 1 to receive the vibration signal transmitted from the vibration sensor 1, convert the vibration signal into a digital vibration signal, perform data acquisition and simple data analysis, and then output the digital vibration signal.
[0036] The control unit 3 is connected to the smart box 2 to receive the digital vibration signal and establish a lubrication failure index based on the vibration change using the Shock Response Spectrum (SRS). When the lubrication failure index changes too much, a lubrication command is output.
[0037] The lubrication unit 4 is connected to the control unit 3 by signal to receive the lubrication command and to perform a lubrication action on the crank bearing G2.
[0038] The second embodiment of the present invention is a method for monitoring the maintenance and lubrication of the crankshaft bearing of an injection molding machine, as shown in Figures 3 and 4. It is implemented in conjunction with the aforementioned system for monitoring the maintenance and lubrication of the crankshaft bearing of an injection molding machine (as shown in Figure 1). It includes the following steps:
[0039] A. A vibration sensor detects the vibration changes of a crankshaft bearing in an injection molding machine and continuously outputs a vibration signal. The vibration sensor 1 can be installed at each position of the crankshaft bearing G2 on the toggle clamping unit G1. During the movement of the toggle clamping unit G1 in closing and opening, the vibration sensor 1 continuously detects the vibration frequency of the crankshaft bearing G2, thereby converting the mechanical motion or energy emitted by the vibration into an electrical signal, and continuously outputting the vibration signal.
[0040] B. A smart set-top box receives the vibration signal and converts it into a digital vibration signal output. The vibration sensor 1 transmits the detected vibration signal containing the vibration frequency to the smart set-top box 2 via wired or wireless means. The smart set-top box 2 stores the vibration signal, processes it using various time-frequency analysis methods, performs filtering, contour data extraction, and simple Fourier transform data analysis, and converts the vibration signal into a digital vibration signal, which is then output. The digital vibration signal contains the vibration frequency.
[0041] C. A control unit receives the digital vibration signal and establishes a lubrication failure index based on the vibration change. When the change in the lubrication failure index is too large, a lubrication command is output. After receiving the digital vibration signal, the control unit 3 uses Shock Response Spectrum (SRS) to analyze the difference between the vibration signals captured in each mold opening and closing cycle, finds the signal difference of the shock response spectrum after the previous lubrication, and analyzes the signal regularity of the shock response spectrum before and after lubrication to establish the lubrication failure index that requires re-lubrication. When the change in the lubrication failure index is too large, re-lubrication is required, and the control unit 3 will output the lubrication command. If the change in the lubrication failure index is not excessive, it means that there is no need to lubricate again, and the vibration signal is directly captured for the next mold opening and closing cycle. By repeatedly detecting and outputting the vibration signal, the lubrication cycle can be automatically adjusted according to the change in the lubrication failure index. Furthermore, the changes in the lubrication failure index can be displayed using an external display device 5, which facilitates direct visual judgment by the operator and serves as a basis for manual lubrication.
[0042] D. An oil injection unit receives the lubrication command and applies an oil injection action to the crank bearing. After receiving the lubrication command, the oil injection unit 4 will automatically lubricate the crank bearing and then continue to capture the vibration signal for the next mold opening and closing cycle.
[0043] This invention involves two experimental tests. Accelerometers are installed on the crankshaft bearing of the same injection molding machine, and cyclic tests of mold opening and closing are performed on the actual machine. Vibration signals are captured during continuous mold opening and closing, and online lubrication cycle analysis is conducted to identify the time points requiring lubrication. This lubrication failure index is established, and lubrication is automatically performed accordingly. After lubrication, real-time analysis of the vibration signals is continuously performed, and changes in lubrication conditions are observed. Lubrication is continuously performed when the signal is abnormal to confirm the effectiveness of the analysis method of this invention. The experimental test requires installing strain gauges on the tie bar of the injection molding machine and installing accelerometers at four positions on the crankshaft bearing. The test confirms that the accelerometer signal from the fixed-end shaft pin is most suitable for analysis. Vibration and strain signal data at the moment of mold opening and closing are extracted, and the vibration signals are analyzed. Real-time analysis is performed for each mold cycle. The time points requiring lubrication are identified, lubrication is performed, and signal changes are observed. Real-time analysis of signal changes between lubrication and the next required lubrication time confirms the effectiveness and repeatability of the method. A lubrication failure index is defined as a parameter for assessing lubrication status when applied to actual machines.
[0044] The results of the second experimental test are shown in Figures 5 and 6. In both real-time tests, new lubricating grease was injected into the crankshaft bearing at the very beginning. During the test, the lubrication failure index was calculated in real-time, and its changes with the number of mold opening and closing cycles and whether or not lubrication was injected were observed. When the test began with the injection of new grease, the health index of the lubrication failure index was low, indicating better lubrication. As the number of mold opening and closing cycles gradually increased, the health index of the lubrication failure index significantly increased and fluctuated. When new grease was injected at the 150th lubrication cycle (as shown in Figure 5), the health index of the lubrication failure index quickly decreased, returning to the same level as at the beginning. However, as the number of mold opening and closing cycles increased, the lubrication failure index rose again. When new grease was injected again at the 330th, 530th, 710th, and 880th cycles (as shown in Figure 5), the lubrication failure index decreased again. The second test occurred at cycles 120, 270, 410, and 540 (as shown in Figure 6). After injecting new grease, the lubrication failure index decreased again.
[0045] The above-mentioned experimental tests show that the shock response spectrum (SRS) method has a significant effect on accurately evaluating the lubrication status of crankshaft bearings.
[0046] As shown in Figure 7, the results obtained when monitoring the lubrication status of the toggle clamping system using the Surge Response Spectrum (SRS) index are segmented and classified. Figure 7 shows that the data distribution typically follows a bathtub curve. After adding lubricating oil to the system, the SRS index decreases rapidly. After decreasing, the SRS index stabilizes for a period known as normal operating life. In the final stage of normal operating life, the wear rate (or failure rate) increases rapidly, causing the SRS index value to rise. This results in excessive fluctuations in the lubrication failure index, at which point the lubrication status changes from "low failure rate" to "gradually increasing failure rate." The lubrication status monitoring system then triggers an alarm, reminding the operator to add oil.
[0047] The detailed explanation of the real-time condition monitoring algorithm of the present invention for determining whether the change of the lubrication failure index is too large is as follows:
[0048] a. Extract the shock response spectrum (SRS) index of the vibration signal of the injection molding machine crankshaft during the mold opening and closing process.
[0049] b. Starting from the 8th switching cycle after the start, the instantaneous rate of change at the 8th point is estimated by the impact response spectrum (SRS) values of the previous 7 switching cycles, that is, the rate of change of the values at this point compared with the previous 7 points.
[0050] c. Repeat step b above for all subsequent injection machine operation cycles.
[0051] d. Starting from the switching cycle at point 71, use the Grubbs test to test for outliers to determine whether the z-value of the instantaneous rate of change exceeds the 95% confidence interval of the distribution. If the z-value is greater than the 95% confidence interval, lubrication is required. If it is less than the 95% confidence interval, lubrication is not required.
[0052] The results obtained by applying the above-described real-time condition monitoring algorithm to segment 1 of Figure 7, as shown in Figures 8 to 10, indicate that the proposed real-time condition monitoring algorithm shows that the z-value at point 71 of the mold-opening cycle is greater than the critical curve value of the Grubbs test, indicating that relubrication is required after point 71 of the mold-opening cycle. The value of the relubrication cycle estimated by this method coincides with the point where the distribution of the impact response spectrum (SRS) index in Figure 7 begins to increase. Therefore, the above-described real-time condition monitoring algorithm is suitable for real-time condition monitoring of the lubrication status of the injection molding machine crankshaft clamping system.
[0053] Based on the above description of the embodiments, the operation, use and effects of the present invention can be fully understood. However, the above embodiments are only preferred embodiments of the present invention and should not be used to limit the scope of the present invention. Simple equivalent changes and modifications made in accordance with the scope of the patent application and the description of the invention are all within the scope of the present invention. [Simplified Explanation of the Diagram]
[0023] [Figure 1] is a schematic diagram of the use of the first embodiment of the present invention.
[0024] [Second Figure] is a block diagram of the configuration of the first embodiment of the present invention.
[0025] [Figure 3] is a flowchart of the method of the second embodiment of the present invention.
[0026] [Figure 4] is an operation flowchart of the second embodiment of the present invention.
[0027] [Figure 5] is a graph showing the relationship between lubrication failure index and lubrication cycle in the first experimental test of this invention.
[0028] [Figure 6] is a graph showing the relationship between lubrication failure index and lubrication cycle in the second experimental test of this invention.
[0029] [Figure 7] is a graph showing the relationship between the impact response spectrum (SRS) index and the number of switching cycles in the experimental test of this invention.
[0030] [Figure 8] is a graph showing the relationship between the impact response spectrum (SRS) index and the number of switching cycles in the experimental test of this invention.
[0031] [Figure 9] is a graph showing the relationship between the instantaneous rate of change at point 8 of the switching mode cycle tested in the present invention.
[0032] [Figure 10] is a graph showing the relationship between the switching mode cycle and the instantaneous rate of change Z value in the experimental test of this invention.
Claims
1. A system for monitoring the maintenance and lubrication of a crankshaft bearing in an injection molding machine, comprising: at least one vibration sensor installed on a crankshaft bearing of an injection molding machine to detect vibration changes in the crankshaft bearing, the vibration sensor outputting a vibration signal based on the detected vibration changes; a smart box connected to the vibration sensor to receive the vibration signal, convert the vibration signal into a digital vibration signal, and then output the digital vibration signal; a control unit connected to the smart box to receive the digital vibration signal, establish a lubrication failure index based on it, and output a lubrication command when the lubrication failure index changes excessively; and an oiling unit connected to the control unit to receive the lubrication command and perform an oiling action on the crankshaft bearing.
2. As in request item 1, a system for monitoring the maintenance and lubrication of the crankshaft bearing of an injection molding machine, wherein, The vibration sensor is an accelerometer.
3. The system for monitoring the maintenance and lubrication of the crankshaft bearing of the injection molding machine as described in Request 1 is further provided with an external display device to display the lubrication failure indicator.
4. A method for monitoring the maintenance and lubrication of a crankshaft bearing in an injection molding machine, comprising the following steps: a vibration sensor detects vibration changes in a crankshaft bearing of an injection molding machine and continuously outputs a vibration signal; a smart box receives the vibration signal and converts it into a digital vibration signal output; a control unit receives the digital vibration signal, establishes a lubrication failure index based on the vibration changes, and outputs a lubrication command when the change in the lubrication failure index exceeds a large value; an oiling unit receives the lubrication command and performs an oiling action on the crankshaft bearing.
5. As in request item 4, the method for monitoring the maintenance and lubrication of the crankshaft bearing of the injection molding machine, wherein, The vibration sensor is installed at the location of the crank bearing, and the vibration sensor is used to detect the vibration changes of the crank bearing at any time.
6. As in request item 4, the method for monitoring the maintenance and lubrication of the crankshaft bearing of the injection molding machine, wherein, After storing the vibration signal, the smart set-top box processes the vibration signal using various time-frequency analysis methods, including filtering, contour data extraction, and simple data analysis using Fourier transform, and then outputs the vibration signal as a digital vibration signal.
7. As in request item 4, the method for monitoring the maintenance and lubrication of the crankshaft bearing of the injection molding machine, wherein, The changes in the lubrication failure index are displayed by an external display device to facilitate direct visual judgment and serve as a basis for manual lubrication.
8. As in request item 4, the method for monitoring the maintenance and lubrication of the crankshaft bearing of the injection molding machine, wherein, After receiving the digital vibration signal, the control unit uses impact response spectrum analysis to analyze the differences between the vibration signals captured in each mold opening and closing cycle. It identifies the signal differences in the impact response spectrum after the previous lubrication and analyzes the signal regularity of the impact response spectrum before and after lubrication. This analysis is used to establish lubrication failure indicators that require re-lubrication. When the change in the lubrication failure indicator is too large, the control unit outputs a lubrication command to apply the lubrication action to the crankshaft bearing, and then performs the vibration signal capture for the next mold opening and closing cycle. If the change in the lubrication failure indicator is not too large, the control unit directly performs the vibration signal capture for the next mold opening and closing cycle.
9. As requested in item 8, the method for monitoring the maintenance and lubrication of the crankshaft bearing of the injection molding machine, wherein... The determination of whether the variation of the lubrication failure index is excessive involves the following steps: a. Extracting the shock response spectrum of the vibration signal during the switching process; b. Starting from the Nth switching cycle after the start, estimating the instantaneous rate of change at the Nth point using the shock response spectrum values of the previous N-1 switching cycles, where N is a positive integer; c. Repeating step b for all subsequent switching cycles; d. Starting from the Mth switching cycle, using the Grubbs test to perform outlier testing to determine whether the z-value of the instantaneous rate of change exceeds the 95% confidence interval of the distribution. If the z-value is greater than the 95% confidence interval, the variation of the lubrication failure index is considered excessive, requiring lubrication; if it is less than the 95% confidence interval, the variation of the lubrication failure index is considered within the acceptable range, and lubrication is not required.
10. As in request item 9, the method for monitoring the maintenance and lubrication of the crankshaft bearing of the injection molding machine, wherein, N=8, M=71.