Gear grinding wheel load estimation device

Abstract

To ensure proper dressing of the grinding wheel and grinding of the tooth surface, the present invention provides a device that can estimate the load applied to the grinding wheel during grinding as accurately as possible. [Solution] A gear grinding wheel load estimation device estimates the load acting on the grinding wheel when grinding the tooth surface by rotating a screw-shaped grinding wheel in contact with the tooth surface to cut the abrasive grains constituting the grinding wheel into the tooth surface. The device is configured to estimate the maximum load applied to the grinding wheel during tooth surface grinding based on a coefficient determined in advance for the grinding wheel, the diameter of the grinding wheel, grinding condition quantities including the feed amount of the grinding wheel to the tooth surface or the amount removed from the tooth surface by one abrasive grain, and the position of the tooth surface in the tooth height direction.

Description

Technical Field

[0001] The present invention relates to an apparatus for estimating the load acting on a grinding wheel for grinding or polishing (hereinafter collectively referred to as grinding) the tooth surface of a gear.

Background Art

[0002] When grinding the tooth surface of a gear, a method for correcting the machining accuracy of a grinding machine is described in Patent Document 1. The outline of the method is to calculate the theoretical tooth profile shape and formulate the dresser shape and the grinding wheel shape. On the other hand, the tooth profile shape is calculated as a three-dimensional approximate tooth profile shape, and the twist angle error is calculated as the difference between the calculated value and the theoretical value. The feed amount of the grinding wheel is set so that the twist angle error falls within the allowable range, and based on this, the dresser shape, the grinding wheel forming conditions, etc. are obtained, and the twist angle error is determined. Thus, correction is performed so that the twist angle error falls within the allowable range. Then, the feed angle between the dresser and the worm grinding wheel is changed so that the error between the calculated value and the theoretical value of the pressure angle decreases.

[0003] Also, it is described in Patent Document 2 that there is a bias in the normal machining resistance in the tooth flank direction position when polishing the tooth surface, and the cycloid locus during actual machining is corrected based on the bias.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The method described in Patent Document 1 is a method for obtaining the desired tooth profile shape by gradually changing the grinding conditions so that the error between the theoretical value and the calculated value is minimized. As a result, the desired tooth profile shape can be obtained by performing the desired grinding. However, the modification of the processing conditions by the method in Patent Document 1 is based on the grinding results, but not on the behavior of the grinding wheel or the gear workpiece during grinding. Therefore, it is not possible to respond to changes in shape due to wear of the grinding wheel during the process of repeatedly grinding the tooth surface after dressing the grinding wheel. For example, even if the worn areas of the grinding wheel are identified and dressing is performed to eliminate the wear, it is difficult to identify all worn areas, so the correction of worn areas may be insufficient. Also, while increasing the amount of material removed by dressing (dressing allowance) can correct worn areas completely, the dressing allowance in that case must be based on experience and may not necessarily be appropriate.

[0006] On the other hand, the bias in the tooth height direction of the normal machining resistance described in Patent Document 2 is thought to affect the wear of the grinding wheel. However, the invention in Patent Document 2 does not take into account the deformation of the grinding wheel caused by the bias in the tooth height direction of the normal machining resistance, or the resulting abnormalities on the tooth surface, and there is room for improvement in terms of rationally performing gear grinding, including grinding wheel dressing.

[0007] The present invention was made against the above-mentioned background, and aims to provide a device that can estimate the load applied to the grinding wheel during grinding as accurately as possible in order to properly dress the grinding wheel and grind the tooth surface. [Means for solving the problem]

[0008] To achieve the above objective, the present invention provides a gear grinding wheel load estimation device that estimates the load acting on a grinding wheel when grinding a tooth surface by rotating a screw-shaped grinding wheel in contact with the tooth surface and cutting the abrasive grains constituting the grinding wheel into the tooth surface, characterized in that it is configured to estimate the maximum load applied to the grinding wheel during grinding of the tooth surface based on a coefficient determined in advance for the grinding wheel, the diameter of the grinding wheel, a grinding condition amount including the feed amount of the grinding wheel to the tooth surface or the amount removed from the tooth surface by one of the abrasive grains, and the position of the tooth surface in the tooth height direction. [Effects of the Invention]

[0009] According to the present invention, when grinding tooth surfaces using the same grinding wheel under the same grinding conditions, it is estimated that the maximum load will vary depending on the position of the target tooth surface in the tooth height direction. More specifically, the load will be greater on the tooth tip side than on the tooth root side. Therefore, wear tends to progress more easily at the bottom of the groove into which the gear teeth are inserted in the grinding wheel. By utilizing this estimation, the dressing amount when dressing the grinding wheel can be determined based on the amount of wear on the groove side, thereby optimizing the dressing amount. Furthermore, it becomes possible to grind the tooth surface to the intended shape using the dressed grinding wheel. In addition, since wear tends to progress more easily at the bottom of the groove of the grinding wheel, it becomes possible to prevent the formation of protrusions on the tip side of the tooth surface by appropriately managing the number of grinding cycles with the same grinding wheel. In other words, tool management or grinding management to avoid the formation of protrusions on the tooth tip side becomes easier. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing the process of grinding gears using a screw-shaped grinding wheel. [Figure 2] This is a schematic diagram illustrating the meshing of the screw-shaped grinding wheel and the gear. [Figure 3] This is a schematic diagram illustrating the process of a single abrasive grain grinding a flat plate. [Figure 4] This is a schematic diagram to explain tangent length. [Figure 5] This is a block diagram illustrating an example of the functional configuration of the estimation device according to the present invention. [Figure 6] This is a schematic diagram illustrating the shape change due to wear of the grooves in a grinding wheel. [Figure 7] This diagram shows the measurement results of the height of the protrusions that form on the tooth tip side when grinding is repeated with the same grinding wheel. [Modes for carrying out the invention]

[0011] Next, embodiments of the present invention will be described with reference to the attached drawings. Note that the embodiments described below are merely examples of how the present invention can be implemented and do not limit the invention.

[0012] Figure 1 is a schematic diagram showing the state in which the tooth surface of a gear (hereinafter simply referred to as a gear) 2 is being ground or polished (hereinafter collectively referred to as grinding) by a screw-shaped grinding wheel (hereinafter simply referred to as a grinding wheel) 1, which is a gear grinding wheel. Figure 2 is a partial view of the state in which the grinding wheel 1 and gear 2 are meshed and grinding is being performed. The teeth 3 of gear 2 are engaged in grooves 4 of the grinding wheel 1, and by rotating the grinding wheel 1 and gear 2 synchronously according to the tooth ratio, the teeth 3 come into contact with the inner surface of grooves 4 and grinding proceeds. As is conventionally known, this grinding is performed by abrasive grains 5 protruding from the surface side of the grinding wheel 1 cutting into the workpiece W and grinding the workpiece W. This state is shown in Figure 3 as an example when grinding a flat plate.

[0013] The amount of work performed by a single abrasive grain 5, the load on the grinding wheel 1, or the maximum cutting depth increases with increasing spacing between abrasive grains 5, the feed rate of the workpiece (flat plate) W, and the thickness being cut, while decreasing with increasing rotational speed of the grinding wheel 1 and the diameter of the grinding wheel. The relationship between the load on the grinding wheel 1 and the grinding conditions or the size of the grinding wheel 1 is the most common, and it is thought that a similar situation occurs when grinding tooth surfaces. However, since the tooth surface of a gear is a curved surface represented by an involute curve, and the area where it is interrupted at the tooth tip is limited, the load situation when grinding tooth surfaces is significantly different from that when grinding a continuous flat plate.

[0014] When grinding a gear tooth surface with a grinding wheel 1, the amount of movement of the grinding wheel 1 in the direction of the rotational axis of the gear being ground is related to the depth of cut. Furthermore, the so-called grinding point (grinding region) where the grinding wheel 1 and the gear tooth surface come into contact changes along the line of action (common tangent), similar to the meshing point of gears, and on the tooth surface, it changes from the tooth root side to the tooth tip side. Therefore, it is thought that the change in the grinding point manifests as a change in the load on the grinding wheel 1.

[0015] Based on the inventors' experience, it has been observed that when tooth surface grinding is continued with the same grinding wheel, as the number of grinding cycles increases, insufficient grinding occurs on the tooth tip side, resulting in the formation of a protrusion. Since grinding of the tooth tip side is performed on the bottom side of the groove 4 on the grinding wheel 1, wear in this area is thought to progress more rapidly than wear in other areas. This is consistent with the inference that a change in the grinding point manifests as a change in the load on the grinding wheel 1, leading to the inference that the maximum depth of cut is maximized when grinding the tooth tip side, and the load on the grinding wheel 1 is maximized when grinding the tooth tip.

[0016] If we express the above considerations in terms of a relational expression for the maximum cutting depth gmax by a single abrasive grain 5, then gmax=F(K,D,f,t,L) Here, K is a coefficient for the grinding wheel 1, which is determined by experiments according to factors such as the spacing between the abrasive grains 5 and the bonding force of the abrasive grains 5 by the binder. D is the diameter of the grinding wheel 1. f is the feed amount of the grinding wheel 1 in the direction of the rotation center axis of the gear. t is the depth cut by one abrasive grain 5, which is the cutting amount of the grinding wheel 1 toward the center side in the radial direction of the gear 2. L is a parameter related to the position on the tooth surface at the grinding point. That is, it can be said that the maximum cutting depth gmax or the maximum load can be grasped by the grinding wheel characteristic factor represented by the coefficient K etc., the grinding wheel shape factor represented by the diameter D etc., the grinding condition amount or grinding condition factor represented by the feed amount f and the cutting amount t etc., and the tooth surface position factor represented by the parameter L etc. related to the position on the tooth surface at the grinding point.

[0017] Here, as an example of a specific mathematical model (or empirical formula) for the maximum cutting depth gmax or the maximum load, gmax = K·2a / π·1 / √D 3 ·f·√t·√L (1) where a is a value corresponding to the spacing between the abrasive grains 5, which is a value obtained in advance by experiments like the coefficient K. Also, L(LA, LC) = √(r(rA, rC) - rb) If this is shown in a figure, it is as shown in Figure 4. r(rA or rC) is the distance (radius) from the center of the gear 2 revolving between the acting line (common tangent) and the tooth surface at point A or point C in Figure 4, and rb is the base circle radius of the gear 2. Hereinafter, L or LA and LC may be referred to as the tangent length.

[0018] The estimation device according to the present invention is configured to determine the load on the grinding wheel 1 using the above-mentioned data or parameters. The estimation device is mainly composed of, for example, a computing element (CPU) and memory elements (RAM, ROM), and is configured to perform calculations using input data and pre-stored data, and to output the result of the calculation. Figure 5 is a block diagram showing the configuration of the estimation device 6 by functional means. The estimation device 6 is equipped with a storage unit 6a, which stores data for multiple grinding wheels that are expected to be used. This data includes pre-prepared data related to the coefficient K and the spacing a between abrasive grains mentioned above, as well as the diameter D of the grinding wheel. The estimation device 6 is also equipped with an input unit 6b for acquiring data from the outside. The data input from the outside is mainly data related to grinding conditions, including the feed amount f of the grinding wheel 1 in the direction of the rotational axis of the gear mentioned above, the depth removed by a single abrasive grain 5, or the cutting depth t of the grinding wheel directed towards the center in the radial direction of the gear 2. Furthermore, the estimation device 6 is equipped with a calculation unit 6c. The calculation unit 6c is a functional means that performs calculations according to a pre-prepared program, and one example of such calculation is the calculation shown in equation (1) above. An output unit 6d is provided in the estimation device 6 to output the result of this calculation. The output format may be as appropriate, such as characters, images, audio, graphs, or electrical signals.

[0019] Figure 6 schematically shows the change in shape due to wear on the side surface of the groove 4 based on the load of the grinding wheel 1 obtained from the above calculation. Figure 6(a) shows the shape of the groove 4 immediately after dressing. When the tooth surface is ground several times with this grinding wheel 1, wear on the side surface progresses so that the groove 4 widens, changing from the initial shape shown by the dashed line in Figure 6(b) to the shape shown by the solid line. Specifically, the wear on the bottom side of the groove 4 becomes greater than the wear on the opening end side (tip side) of the groove 4. Furthermore, if grinding is continued, as shown in Figure 6(c), the bottom side of the groove 4 wears down significantly, and the groove width widens at the bottom. With such a grinding wheel 1, the grinding of the gear tooth tip that contacts the bottom side of the groove 4 is not sufficiently performed.

[0020] Such a situation manifests as an abnormality in the shape of the tooth surface. Figure 7 shows the results of measuring the amount of protrusion (convexity) from the reference surface of a specific portion on the tooth tip side after performing tooth surface grinding multiple times with the same grinding wheel. The reference surface is a surface of the tooth surface with a shape determined by the design, or a surface created by grinding. In Figure 7, the horizontal axis represents the number of processes, and the vertical axis represents the amount of protrusion. As mentioned above, the side surface of groove 4 wears down each time it is ground, but the amount of wear is greater on the bottom side of groove 4, so grinding on the tooth tip side of the tooth surface gradually stops progressing. As a result, as shown in Figure 7, the amount of protrusion from the reference surface on the tooth tip side gradually increases. In other words, it was found that the estimation results by the estimation device 6 according to the present invention match the actual wear results corresponding to the grinding load.

[0021] As described above, according to the present invention, the wear condition of the grinding wheel that creates the tooth profile can be accurately grasped, so that the tooth profile obtained by grinding can be made into the shape intended in the design. In particular, since the cause of the protrusion that occurs on the tooth tip side can be elucidated, it is possible to obtain gears with no errors in the tooth profile, and consequently, gears with less damage, abnormal noise, or noise can be obtained. Furthermore, since the dressing amount of the grinding wheel can be optimized, the life of the grinding wheel can be improved and tool costs can be reduced. Moreover, in the present invention, the load on the grinding wheel can be grasped by the relationship formula of the tangent length L, so the grinding (polishing) error can be accurately grasped, for example, between small-diameter gears with a small pitch circle diameter and large-diameter gears with a large pitch circle diameter, and the tooth surface shape can be optimized regardless of the size of the pitch circle diameter.

[0022] The estimation device according to the present invention can be configured as an independent device, but it can also be incorporated into a tooth surface grinding machine or a device for dressing grinding wheels. Furthermore, in the present invention, a parameter that reflects the position of the grinding area in the tooth height direction may be used to estimate the load on the grinding wheel, and therefore, this parameter may be a parameter other than the square root of the tangent length L mentioned above. [Explanation of Symbols]

[0023] 1 whetstone 2 gears 3 teeth 4 grooves 5 abrasive grains 6 Estimation device 6a Storage section 6b Input section 6c Arithmetic section 6d output section

Claims

[Claim 1] A gear grinding wheel load estimation device that estimates the load acting on the grinding wheel when grinding the tooth surface by rotating a screw-shaped grinding wheel in contact with the tooth surface and cutting the abrasive grains constituting the grinding wheel into the tooth surface, The system is configured to estimate the maximum load applied to the grinding wheel during tooth grinding, based on a coefficient determined in advance for the grinding wheel, the diameter of the grinding wheel, grinding conditions including the feed rate of the grinding wheel to the tooth surface or the amount removed from the tooth surface by a single abrasive grain, and the position of the tooth surface in the tooth height direction. A gear grinding wheel load estimation device characterized by the following features.

Images