A method for judging tool capability based on feed axis motor phase current

Abstract

The present invention relates to a method for judging the capability of a tool based on the phase current of a feed shaft motor, which solves the problem that there is a lack of direct judgment criteria in the application process of current tools. The present invention comprises the following steps: Step 1, collecting the current i of the first phase of the feed shaft motor a , the current of the second phase i b And the third phase current i c ; Step 2, through i a 、i b with i c , calculate the motor rotor current I r ; Step 3, according to the rotor current I r Calculate the mean value μ of the rotor current in the rough rolling stage cc , the mean value of the rotor current μ in the fine rubbing stage jc And the mean value μ of the rotor phase current during the exit phase tc ; Step 4, through μ cc , μ jc and μ tc Calculate the variance s of the rotor current in the rough rolling stage respectively cc , the variance of the rotor current in the fine rubbing stage s jc and the rotor current s in the exit phase tc ; Step 5, through the mean value μ of the rotor current in the rough rubbing stage cc , the mean value of the rotor current μ in the fine rubbing stage jc The mean value μ of the rotor current during the exit phase tc The relationship between them can be used to determine whether the tool meets the requirements.

Description

Technical Field

[0001] The invention relates to a method for judging whether a tooth rubbing force is qualified, and in particular to a method for judging the capability of a tool based on the phase current of a feed shaft motor. Background Art

[0002] Gear rolling is a precision plastic forming method that evolved from the principle of meshing between involute gears and racks and is widely used in the processing of spline parts. Figure 1 and Figure 2 As shown, during the gear rolling process, the workpiece 2 is clamped by the front center 1 and the rear center 3, so that the workpiece 2 is located between the upper plate 51 and the lower plate 52 of the gear rolling cutter 5. The upper plate 51 and the lower plate 52 are both mounted on their respective corresponding workbenches 6, and the workbench 6 is mounted on the ball screw feed system 7. The ball screw feed system 7 is provided with a motor 4. The upper plate 51 and the lower plate 52 rotate in opposite directions to finally complete the processing of the workpiece 2. The upper plate 51 and the lower plate 52 of the gear rolling cutter 5 are divided into three parts: rough rolling, fine rolling and exit, so as to ensure that the gear rolling cutter 5 can complete the whole process of rough and fine processing of the spline with one movement.

[0003] It can be known from the principle of gear rolling processing that the parameters such as tooth height, tooth thickness and pressure angle of the three parts of rough rolling, fine rolling and withdrawal are determined by the parameters such as the number of teeth, module and span of the spline. Therefore, it is necessary to redesign different gear rolling cutters 5 to process splines with different parameters. In addition, the newly designed gear rolling cutter 5 needs to be tested for many times to verify its influence on the processing accuracy, quality and tool life. In particular, the different design parameters of the gear rolling cutter 5 result in different forces on the upper plate 51 and the lower plate 52 at different stages. The different forces at different stages will affect the service life of the tool. However, life tests are very time-consuming. In the case of heavy tasks in developing new products and different material selection, manufacturers rarely conduct life tests, which seriously affects the production cost and processing efficiency of users.

[0004] In summary, due to the lack of effective calculation models and measurement methods for directly observing the gear rolling cutter force, it is impossible to directly determine whether the force generated by each section of the gear rolling cutter is reasonable. If the force generated by each section of the gear rolling cutter is unreasonable, the workpiece will be prone to broken teeth, which will seriously affect the service life of the tool and increase the processing cost of the tool.

[0005] A Chinese invention with publication number CN114004042A discloses an efficient cutting parameter optimization method for rough machining of difficult-to-machine materials that integrates tool wear monitoring. This method has complicated steps and many variables to consider, and is not suitable for simple judgment environments. Summary of the invention

[0006] The present invention provides a method for judging the tool capacity based on the phase current of a feed shaft motor, which is used to solve the problem of lack of a method for measuring the force on a gear rolling tool and a judgment standard.

[0007] In this invention, the failure phenomenon and law of gear rolling tools are first analyzed in the gear rolling process. Secondly, the relationship between the motor phase current of the feed system and the gear rolling force is established through a three-phase AC motor model, and the change law of the gear rolling force in the gear rolling process is studied. Finally, statistical analysis indicators are proposed based on the obtained laws. ， The forces generated by the gear rolling tool during the rough rolling, fine rolling and withdrawal stages are analyzed to determine whether the tool design is reasonable, thereby indirectly improving the tool life.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for judging tool capability based on feed axis motor phase current, which is special in that it includes the following steps:

[0010] Step 1: collect the current i of the n first phases of the feed axis motor in the rough rubbing stage, the fine rubbing stage and the exit stage respectively. a , the current i of n second phases b and the current i of the n third phases c ;

[0011] Step 2: The current i of the n first phases collected during the rough rubbing stage, the fine rubbing stage, and the exit stage a , the current i of n second phases b and the current i of the n third phases c , calculate the motor rotor current I collected in the n rough rubbing stages, fine rubbing stages and exit stages r ;

[0012] Step 3: Based on the n rotor currents I collected during the rough rubbing stage, the fine rubbing stage, and the exit stage r Calculate the mean value μ of the rotor current in the rough rolling stage cc , the mean value of the rotor current μ in the fine rubbing stage jc And the mean value μ of the rotor phase current during the exit phase tc ;

[0013] Step 4: The mean value μ of the rotor current during the rough rolling phase cc , the mean value of the rotor current μ in the fine rubbing stage jc And the mean value μ of the rotor current during the exit phase tc Calculate the variance s of the rotor current in the rough rolling stage respectively cc , the variance of the rotor current in the fine rubbing stage s jc and the rotor current s in the exit phase tc ;

[0014] Step 5, if: μ cc ≥max(μ jc ,μ tc ),s jc ≤min(s cc ,s tc ) and K≥ξ meet the requirements, then the tool capability is judged to meet the requirements;

[0015] Where K is the tool threshold selection index, ξ is the tool threshold.

[0016] Furthermore, in step 3, the mean value μ of the rotor current in the rough rubbing stage is calculated by the following formula: cc , the mean value of the rotor current μ in the fine rubbing stage jc And the mean value μ of the rotor current during the exit phase tc ;

[0017]

[0018]

[0019]

[0020] Among them, I r,i,cc is the current of the motor rotor at any time during the rough rubbing stage, I r,i,jc is the current of the motor rotor at any time during the fine rubbing stage, I r,i,tc is the motor rotor current at any time during the exit phase, n is I r,i,cc ,I r,i,jc and I r,i,tc The quantity value of .

[0021] Furthermore, in step 4, the variance s of the rotor current in the rough rolling stage is calculated by the following formula: cc , the variance of the rotor current in the fine rubbing stage s jc and the variance s of the rotor current during the exit phase tc ;

[0022]

[0023]

[0024]

[0025] in, is the average value of the motor rotor current in the rough rubbing stage, is the average value of the motor rotor current during the fine rubbing stage, is the average value of the motor rotor current during the exit phase.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention can evaluate the tooth rolling force through the rotor current of the feed shaft motor in the test cutting process, quickly and accurately select the tool with the optimal design parameters, and reduce the production cost. In addition, the present invention does not require a dedicated test bench or a dedicated sensor for measurement and analysis, which reduces the number of test tools and increases the number of places where it can be directly used. It also fills the gap in the analysis of the changing law of tooth rolling force during the processing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the gear rolling process;

[0029] Figure 2 It is a schematic diagram of the structure of the workpiece being clamped during the gear rolling process;

[0030] Figure 3 Schematic diagram of a simplified model of a stator and a rotor in an embodiment of the present invention;

[0031] Figure 4 is a diagram showing the magnetic potential relationship between the stator and the rotor in an embodiment of the present invention;

[0032] Figure 5 Schematic diagram of a three-phase stator winding in a dq coordinate system under a stator reference system in an embodiment of the present invention;

[0033] Figure 6 It is a schematic diagram of changes in the mean index and variance index of the phase current corresponding to the first gear rolling tool in an embodiment of the present invention;

[0034] Figure 7 Schematic diagram of changes in the mean index and variance index of the phase current corresponding to the second gear rolling tool in an embodiment of the present invention.

[0035] The reference numerals are as follows:

[0036] 1. Front center, 2. Workpiece, 3. Rear center, 4. Motor, 5. Gear rolling cutter, 51. Upper plate, 52. Lower plate, 6. Workbench, 7. Ball screw feed system. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods.

[0038] A method for judging tool capability based on feed axis motor phase current, the specific steps are as follows:

[0039] Step 1: Analysis of gear rolling tool failure phenomenon.

[0040] During the gear rolling process, Figure 1 and Figure 2As shown, the upper plate 51 and the lower plate 52 of the gear rolling cutter 5 will generate cutting force and cutting heat when they are in extrusion contact with the workpiece 2, causing the teeth on the upper plate 51 and the lower plate 52 to wear under the action of thermal-mechanical coupling. After the teeth are worn, the cutting force will increase, which will in turn cause the impact and vibration to intensify during the processing, and eventually lead to the failure of the teeth. When the gear rolling cutter 5 is not designed properly, it will lead to an imbalance in the forces of the rough rolling, fine rolling and exiting parts. The pressure and frictional heat generated during the extrusion process can easily cause the teeth to break, reducing the service life of the tool. In extreme cases, the teeth in the fine rolling stage broke under normal wear.

[0041] Step 2: Analyze the changing pattern of tooth rubbing force.

[0042] Through the analysis of the failure phenomenon of the gear rolling cutter 5, it can be seen that the unreasonable design of the parameters such as the tooth height, tooth thickness and pressure angle of the three parts of the rough rolling, fine rolling and withdrawal in the upper plate 51 and the lower plate 52 caused the cutter teeth to be subjected to excessive impact force, and the cutter teeth broke, which eventually led to the failure of the gear rolling cutter 5. Due to the structural characteristics of the gear rolling cutter 5, it is impossible to place a force sensor to directly measure the magnitude of the three parts of the rough rolling, fine rolling and withdrawal, so the feed shaft motor phase current is used to indirectly reflect the change law of the three parts of the gear rolling cutter force.

[0043] Step 3, calculate and show the relationship between the motor rotor current and the output torque.

[0044] According to the principle of electromagnetic induction, when a three-phase symmetrical current is passed through the stator winding, the three-phase symmetrical current means that the amplitude of the three-phase current is equal and the phase lags behind by 120°. A rotating magnetic field will be generated inside the motor. The magnetic potential of the magnetic field can be expressed as F s The magnetic potential of the motor rotor is expressed as F r Therefore, when the motor is working, the excitation magnetic potential F m It can be expressed by formula (1):

[0045] F m =F s -F r (1)

[0046] When the motor is running under load, the rotor current increases. In order to offset the magnetic potential generated by the rotor current, the stator current must also increase accordingly, ultimately ensuring the excitation magnetic potential F m According to the above analysis, the motor is simplified, assuming that the air gap of the motor is uniform, and the radial gap between the stator and the rotor is g, such as Figure 3 and Figure 4 As shown, the combined air gap magnetic potential F generated by the stator winding and the rotor winding is sr It can be expressed by formula (2):

[0047] F sr =g·H(2)

[0048] Where: H is the magnetic field strength.

[0049] Considering that the average value of the square of a sine wave is half its amplitude, the total magnetic energy density W fld The average magnetic energy density The product of and the air gap volume V is shown in the following formula (3):

[0050]

[0051] Where: μ0 is the magnetic permeability; B is the magnetic induction intensity.

[0052] Depend on Figure 4 From the magnetic potential vector diagram, we can see that the composite air gap magnetic potential Therefore, the total magnetic energy density can be expressed by formula (4):

[0053]

[0054] Where: sr is the electrical angle difference between the stator and the rotor.

[0055] From the magnetic potential balance of the asynchronous motor, it can be seen that keeping the magnetic potential constant is equivalent to keeping the current constant. In addition, the air gap flux generated by the rotor current rotates synchronously with the air gap flux generated by the stator current, that is, they are relatively stationary. The air gap flux generates a stable torque to maintain the rotor rotation, and the electromagnetic torque can be used as the output torque of the motor rotor. Therefore, formula (4) is converted into the total magnetic energy density W fld The angle δ between the axis of the synthetic magnetic potential and the axis of the rotor magnetic potential r By finding the partial derivative, the electromagnetic torque T can be expressed by formula (5):

[0056]

[0057] Considering the synthetic air gap magnetic potential F sr The magnetic flux generated Φ sr =(2V / π)B sr , and the magnetic induction intensity B sr =μ0F sr / g, synthetic magnetic potential F sr It can be expressed as:

[0058]

[0059] Substituting formula (6) into formula (5), the electromagnetic torque T is expressed as follows:

[0060]

[0061] The magnetic potential of the motor rotor Where m r ,Nr ,k wr , p is a constant, F r and rotor current I r In addition, the rotor magnetic potential lags the synthetic air gap flux by approximately 90° electrical angle, sinδ r ≈-1, magnetic flux Φ sr Therefore, the motor output torque T m It can be expressed by formula (8):

[0062] T m =K t I r (8)

[0063] Where: I r is the rotor current; K t is the torque coefficient / Nm·A -1 .

[0064] Step 4, calculate the relationship between the motor phase current and the rotor current.

[0065] The relationship between the motor rotor current and the motor output torque is obtained by formula (8), but in fact the motor rotor current cannot be obtained and can only be calculated by the phase current. According to the characteristics of three-phase alternating current, it can be expressed by formula (9):

[0066]

[0067] I is the total current of the feed axis motor, θ r is the electrical angle, i a is the current of the first phase of the three-phase current of the feed axis motor, i b is the current of the second phase of the three-phase current of the feed axis motor, i c It is the current of the third phase among the three-phase current of the feed axis motor.

[0068] In addition, the three-phase stator current, three-phase rotor current and their corresponding magnetic potential can be converted into a single stator current vector, rotor current vector and corresponding magnetic potential vector, so that these phasors are considered to be generated by a stator winding and rotor winding. The current and magnetic potential on the three-phase winding can be decomposed into two mutually perpendicular virtual coordinate axes, such as Figure 5 The quadrature axis q and the direct axis d of the three-phase winding are shown in Figure 1. Therefore, the AC motor can be equivalent to a separately excited DC motor. Figure 5 As shown in the figure, the two-phase system and the three-phase system generate equal magnetic potential and current amplitude as the equivalent criterion (equal power), and the current decomposed into the dq axis is a current vector with a constant amplitude and rotating at a synchronous angular velocity. Since the d-axis current amplitude approaches 0, the q-axis current is expressed as the rotor current, that is, the three-phase current is decomposed along the d-axis and q-axis directions of the rotor to obtain the d-axis current Id ≈0 and the q-axis current I q =I r , which can be expressed by formula (10).

[0069]

[0070] Substituting formula (9) into formula (10), the q-axis current I of the rotor is q =I r The relationship between and the stator three-phase current can be expressed by formula (11):

[0071]

[0072] Substituting formula (11) into formula (8), the relationship between the motor output torque and the stator rotor current can be expressed by formula (12).

[0073]

[0074] Step 5: Calculate the relationship between the motor output torque and the gear rolling force

[0075] For the feed system, the motor output torque not only needs to overcome the force generated during the gear rolling process, but also needs to overcome the friction between the ball screw and the guide rail slider pair and the inertia force of the feed system. Therefore, the magnitude of the feed system motor output torque can be expressed by formula (13).

[0076] T m =T a +T f +T c (13)

[0077] Where: T a is the moment of inertia (0 at uniform speed); T f is the friction torque; T c is the gear rubbing torque.

[0078] When the feed speed remains unchanged, T a is 0, T f is a constant value, the motor output torque T m The change is caused by the gear rolling torque T c Therefore, by monitoring the phase current of the feed axis motor, the change of the torque generated during the gear rolling process can be obtained.

[0079] Step 6: Extraction of motor phase current statistical analysis indicators

[0080] According to the above analysis, the phase current of the feed axis motor can reflect the change of the gear rolling force during the gear rolling process, and the change of the gear rolling force can be fed back to the feed axis motor. Therefore, for the collected three-phase current of the feed axis motor, the mean value μ(I r ) and the variance of the rotor current s(I r ). For the convenience of comparison, two gear rolling tools with different geometric parameters are used to process the same part with the same processing parameters. The mean and variance change trends of each stage are shown in Figure 6 and Figure 7 The processing parameters and conditions are shown in Table 1.

[0081] Table 1 Processing parameters

[0082]

[0083] from Figure 6 and Figure 7 The results obtained in the figure show that the changing trends of indicators of different gear rolling tools in the rough rolling, fine rolling and exit parts are different. In order to select the optimal gear rolling tool, a more in-depth comparative analysis of the mean and variance of the rotor current is required.

[0084] Step 7: Analysis of motor phase current statistical analysis indicators

[0085] According to the physical meaning of the mean value of the rotor current and combined with the actual processing situation, the mean value of the rough rolling part should be greater than that of the fine rolling and exiting parts. In the exiting part, due to the instability of the tooth rolling process, its mean value will be slightly larger than that of the fine rolling part, which can be expressed by formula (14). For the variance index, it represents the magnitude of the fluctuation amount in each stage, and the magnitude of the phase current fluctuation amount means the impact degree of the workpiece on each stage. The smaller the variance, the smaller the impact of the cutter teeth, which is very helpful to extend the tool life. The analysis condition can be expressed by formula (15).

[0086]

[0087] Among them: max is the maximum operation function; μ cc is the mean value of the rotor current in the rough rubbing stage; μ jc is the mean value of the rotor current in the fine rubbing stage; μ tc is the mean value of the rotor current in the exit phase; I r,i,cc is the current of the motor rotor at any time during the rough rubbing stage; I r,i,jc I is the current of the motor rotor at any time during the fine rubbing stage; r,i,tc is the motor rotor current at any time during the exit phase; n is I r,i,cc ,I r,i,jc and I r,i,tc The quantity value of .

[0088]

[0089] Among them: min is the minimum operation function; s cc is the variance of the rotor current in the rough rolling stage; s jc is the variance of the rotor current in the fine rubbing stage; s tc is the variance of the rotor current in the exit phase; is the average value of the motor rotor current in the rough rubbing stage; is the average value of the motor rotor current during the fine rubbing stage; is the average value of the motor rotor current during the exit phase.

[0090] A selection index K is also provided, which can be expressed by formula (16).

[0091]

[0092] Where: K is the selection index; ξ is the threshold corresponding to the selection index during tool design.

[0093] If the mean, variance and selection index of each stage in the gear rolling process meet the requirements, the tool can be used; if any one of them does not meet the judgment conditions, the tool parameters need to be redesigned.

Claims

1. A method for judging tool capability based on feed axis motor phase current, characterized in that: The steps include: Step 1: collect the current i of the n first phases of the feed axis motor in the rough rubbing stage, the fine rubbing stage and the exit stage respectively. a , the current of the second phase i b And the third phase current i c ; Step 2: The current i of the n first phases collected during the rough rubbing stage, the fine rubbing stage, and the exit stage a , the current i of n second phases b and the current i of the n third phases c , calculate the motor rotor current I collected in the n rough rubbing stages, fine rubbing stages and exit stages r ; Step 3: Based on the n rotor currents I collected during the rough rubbing stage, the fine rubbing stage, and the exit stage r Calculate the mean value μ of the rotor current in the rough rolling stage cc , the mean value of the rotor current μ in the fine rubbing stage jc And the mean value μ of the rotor phase current during the exit phase tc ; Step 4: The mean value μ of the rotor current during the rough rolling phase cc , the mean value of the rotor current μ in the fine rubbing stage jc And the mean value μ of the rotor current during the exit phase tc Calculate the variance s of the rotor current in the rough rolling stage respectively cc , the variance of the rotor current in the fine rubbing stage s jc and the rotor current s in the exit phase tc ; Step 5, if: μ cc ≥max(μ jc ,μ tc ),s jc ≤min(s cc ,s tc ) and K≥ξ meet the requirements, then the tool capability is judged to meet the requirements; Where K is the tool threshold selection index, ξ is the tool threshold.

2. The method for judging tool capability based on feed shaft motor phase current according to claim 1, characterized in that: In step 3, the mean value μ of the rotor current in the rough rolling stage is calculated by the following formula: cc , the mean value of the rotor current μ in the fine rubbing stage jc And the mean value μ of the rotor current during the exit phase tc ; Among them, I r,i,cc is the current of the motor rotor at any time during the rough rubbing stage, I r,i,jc is the current of the motor rotor at any time during the fine rubbing stage, I r,i,tc is the motor rotor current at any time during the exit phase, n is I r,i,cc ,I r,i,jc and I r,i,tc The quantity value of .

3. The method for judging tool capability based on feed shaft motor phase current according to claim 1, characterized in that: In step 4, the variance s of the rotor current in the rough rolling stage is calculated by the following formula: cc , the variance of the rotor current in the fine rubbing stage s jc and the variance s of the rotor current during the exit phase tc ; in, is the average value of the motor rotor current in the rough rubbing stage, is the average value of the motor rotor current during the fine rubbing stage, is the average value of the motor rotor current during the exit phase.

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