CN100335818C - Arc surface calibratkon cam mechanism and its processing method - Google Patents

Abstract

The invention relates to an arc surface indexing cam mechanism and its processing technology. The cam profile of the cam mechanism includes a positioning section, a transition section and an indexing section, and is characterized in that the transition section and the indexing section of the cam profile are concave surfaces, and the matching rollers engaged with it have a radius of curvature smaller than that of the convex surface. Drum type rollers with a concave radius of curvature on the profiled surface. The processing method includes a linkage control method between the cam rotation axis z ₁ and the tool rotation axis z ₂ , and is characterized in that the processing method is a single-side four-coordinate linkage processing tool position control method; that is, the cam rotation axis z ₁ and the tool While the rotation axis z ₂ works in conjunction, the tool also moves in a straight line along the y ₂ and z ₂ coordinates.

Description

A curved surface indexing cam mechanism and its processing method

technical field

The invention relates to a mechanical cam mechanism, specifically an arc-surface indexing cam mechanism and a processing method thereof, and the international patent classification number is proposed to be Int.Cl ⁷ .F16H 37/00.

Background technique

The arc indexing cam mechanism is an ideal indexing mechanism suitable for high-speed and high-precision work occasions. The arc surface indexing cam mechanism currently produced and used is basically a cylindrical roller follower. Through the analysis of its mechanical structure and meshing characteristics, it can be seen that even in the theoretical meshing state, the contact between the cylindrical roller and the cam surface cannot achieve pure rolling. The reason is that when the cam rotates at a constant angular velocity, the farther it is from the cam axis, the greater its movement speed, so the two sides at a certain point on the contact line between the meshing roller and the cam will slip in opposite directions, making the contact Surface, that is, the positioning section of the cam profile, the transition section and the indexing section produce uneven wear or tearing, among which the wearing or tearing of the indexing section is the most serious, so that the vibration and vibration of the cam mechanism during movement The noise is increased, and the transmission accuracy and service life of the mechanism are also reduced. The main reasons are:

1. There is a serious sliding or slipping phenomenon between the cylindrical roller follower and the cam profile surface during the movement, which causes the cam surface to wear;

2. The line contact between the cylindrical roller follower and the cam profile surface is very sensitive to machining errors. After actual machining, the contact state is difficult to reach the ideal contact state in theoretical design;

3. The cylindrical roller follower is in contact with both sides of the cam profile at the same time, which intensifies the wear of the roller and the cam surface. In addition, from the processing point of view, the processing of the traditional cam profile surface cannot be ground, resulting in a large cam profile surface roughness, which is easy to cause wear, vibration and noise; after a period of use, the meshing gap increases, which intensifies wear and vibration and noise.

At present, the key factor that restricts the arc indexing cam mechanism and makes it difficult to popularize is the accuracy guarantee of the arc indexing cam mechanism. Domestically produced cams are only suitable for medium and low speed motions, and have a short lifespan. The reason for this is that, on the one hand, there is a design problem of the arcuate indexing cam mechanism, and on the other hand, the processing method of the arcuate indexing cam is also an important issue.

In the past, the machining of the curved surface indexing cam surface was carried out by profiling, indexing and marking milling, etc. These methods can only roughly process the convex surface, and the product is difficult to apply to high-speed and high-precision workplaces. The profile of the arc-shaped indexing cam belongs to the helical surface that cannot be developed in space, and it is difficult to process. Theoretically speaking, the following methods can be adopted for the processing of the arc surface indexing cam profile:

(1) Treat the cam profile as a free-form surface, and use a face milling cutter or a ball nose cutter for point-to-point processing, which can realize non-equal-diameter machining on one side of the profile (as shown in Figure 4). The disadvantage of this method is that the original envelope relationship between the cam and the roller has been lost between the cam and the cutter, the control process is complicated, the milling cutter and the cam surface are in point contact, the processing efficiency is low, the surface quality is poor, and the amount of data processing Large, which inevitably results in large processing errors;

(2) The profile surface is processed according to the envelope principle on a general-purpose machine tool such as a five-coordinate linkage CNC machining center. The disadvantage of this method is that the adjustment of the machine tool is more complicated and the cost is higher, and it is suitable for single-piece, small-batch processing or repairing;

(3) Use a hobbing machine or a special machine tool modified by other machine tools to process the arc indexing cam. The disadvantage of this method is that affected by the precision of the original machine tool, the precision of the processed arc indexing cam is low, which cannot meet the requirements of high-speed movement, and the processing capacity is also limited;

(4) Special CNC machine tool processing (principle shown in Figure 5). It is an effective way to improve machining accuracy and efficiency by using special CNC machine tool to process arc indexing cam, and it will become the main processing form of arc indexing cam in the future.

At present, the arc indexing cam processed by special-purpose and general-purpose machine tools or modified machine tools in China is only suitable for medium and low-speed motion occasions. The general process is: in the rough machining stage, a milling cutter with a diameter smaller than the roller is used, and in order to improve the cutting efficiency, a large feed rate is used for milling; in the final finishing milling process, a milling cutter with the same diameter as the roller is used, Program with follower roller center movement path. With such a processing technology, there is no theoretical error on the cam profile, and no tool compensation is performed during processing. The main reason is that the contact line of the space cam is a space curve (see Figure 6). When the size of the tool is not equal to the size of the roller, the actual contact line L _t between the tool and the cam and the theoretical contact line L _k between the roller and the cam are spatial curves located on different cylindrical surfaces, rather than straight lines, so it cannot be adopted The method of tool radius compensation makes it completely coincident. Except for the special segment, the convex contour surface is not a normal straight contour, and it is a non-developable spatial surface. When machining the profile of the space cam, only the tool with the same geometric parameters as the follower roller can theoretically process the cam profile without error.

According to this processing principle, the accuracy of the groove width of the cam body depends entirely on the sharpening accuracy of the tool. The tool needs to be specially made, and the following factors will inevitably bring many difficulties to the processing, and some factors are difficult to overcome:

(1) Tool wear: The cam mechanism is a high pair and wears quickly. In order to improve its service life, the cam is generally made of alloy steel, which not only has high hardness but also has high toughness, and the tool wears faster during processing;

(2) Limitation of the number of tools in the tool magazine: the size of the follower roller is generally the standard size or the size determined according to the specific structure during design, so it is difficult to find the corresponding tools completely, and it is undoubtedly increased to order standard tools manufacturing cost;

(3) The factor of the width of the cam groove: If the size of the cam groove is large according to the specific needs, it is unrealistic to manufacture a large tool. Even if such a large tool can be manufactured, it is also limited by the power and structure of the machine tool during processing;

(4) Influence of milling method: Both sides of the tool participate in milling at the same time, one side is down milling, and the other side must be up milling, which makes the quality of the processed profile uneven or uneven. The surface roughness and machining accuracy of the general milling method are relatively high during down milling, and can prevent machining chatter;

(5) Factors of cutting speed: The machining process of two-coordinate linkage makes the cutting speed of the tool not constant on different curve segments of the cam and different gyration radii, so it will seriously affect the surface quality of the cam and the service life of the tool;

(6) The machining allowance is difficult to control: the determination of the general machining allowance is based on relevant parameters, such as workpiece material and tool conditions, and can only be finally determined after trial cutting. Constant speed cutting, while smaller depth of cut and feed rate can obtain higher machining accuracy; high speed cutting and smaller depth of cut and feed rate can obtain smaller surface roughness. The machining allowance determined according to this requirement requires more special tools in rough machining, semi-finishing and finishing machining, otherwise it will have a great impact on the processing quality of the profile surface and the service life of the tool;

(7) Difficult to achieve grinding: It is difficult to achieve grinding of the profile surface according to the aforementioned equal-diameter processing method. The reason is that the service life of the emery wheel is very short due to factors such as wear and trimming after using for a period of time, which must increase the manufacturing cost of the cam. What's more, according to the principle of equal-diameter processing, the grinding wheel grinds the two sides of the cam at the same time, and the radial force is very large, so the grinding wheel is easily crushed; the uneven margin on both sides of the profile surface also easily causes the grinding head to shift. Affect the grinding accuracy; Insufficient cooling can easily burn the surface of the cam, etc.

As mentioned above, grinding is the main finishing form of the space cam, and it is difficult to process the inner groove surface of the space cam according to the principle of equal diameter machining.

A relatively advanced solution at home and abroad is to use a planetary grinding head. For example, the two-coordinate linkage CNC grinding machine produced by the German SCHIESS.KOPP company is equipped with this mechanism. Its working principle is shown in Figure ₇ : the grinding wheel rotates around o While the profile is grinding, planetary motion is performed around o ₁ , and r _w +o ₁ o ₂ = r, r _w and r are the radii of the grinding wheel and the roller respectively. Since the processing of this mechanism is discontinuous, there are ripples on the convex contour surface after processing, and the lower the revolution speed, the greater the waviness, so the revolution speed is required to be high; and the eccentric mechanism at high speed is prone to vibration, making The adjustable amount o ₁ o ₂ is very small; at the same time, the structure of the planetary grinding head is very complicated and the price is very expensive, the processing cost of the product must be high, and the application and promotion are difficult.

With the development of automatic production lines and automatic machinery, the application of high-speed and high-precision space cams is gradually increasing. Based on the above reasons, the research design is ingenious, the structure is reasonable, and the arc-shaped indexing cam mechanism suitable for high-speed motion is easy to process and high precision. A low-cost processing method is a very necessary and urgent task.

Contents of the invention

Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to design a new type of arc surface indexing cam mechanism, which has many advantages such as simple structure, convenient processing, small wear, low noise, long life, etc., especially for The processing error tolerance is strong, which is beneficial to ensure the indexing and positioning accuracy of the cam mechanism, and improves the motion and dynamic performance of the cam mechanism.

Another technical problem to be solved by the present invention is to design a processing method for the arc-shaped indexing cam mechanism, which has the advantages of easy processing, high precision, convenient adjustment, good economy, and the use of conventional equipment.

The technical solution of the present invention to solve the technical problem of the arcuate indexing cam mechanism is to design an arcuate indexing cam mechanism, which includes a cam and matching rollers engaged with it, and the cam profile includes a positioning section, a transition section and a pointing section. The transition section and the indexing section of the convex profile are concave, and the matching rollers engaged with it are drum-shaped rollers whose curvature radius is smaller than the curvature radius of the concave surface of the convex profile, and the feature is that the convex profile In the surface transition section and indexing section, the mn section, c'e section and fg section shown in Figure 10 are thinned by 0.02-0.04mm along their normal direction; or in the convex profile surface transition section and indexing section As shown in Figure 10, the mn segment and eh segment are thinned by 0.02-0.04 mm along their normal direction.

The design feature of the arc surface indexing cam mechanism of the present invention is that the transition section and the indexing section of the cam profile are designed as concave surfaces, and at the same time, the driven cylindrical rollers meshing with it are correspondingly changed to have a radius of curvature smaller than that of the cam profile. Drum rollers with a concave radius of curvature. This design can upgrade the linear meshing movement of the conventional cylindrical roller follower and the cam profile to the point meshing movement of the present invention, so that the cam mechanism has a point meshing pure rolling pair transmission with strong error tolerance It is beneficial to ensure the accuracy of indexing and positioning of the cam mechanism, improve its motion and dynamic performance, and also increase the service life of the cam mechanism. Obviously, this design also has the advantages of simple structure, convenient processing, less wear, and low noise. At the same time, the matching design of the concave surface of the convex profile surface and the convex surface of the drum-shaped roller is helpful for improving the lubrication between the conjugate surfaces. It has a good effect on both the stress state and the arc surface indexing cam mechanism, which can further reduce the wear of the arcuate indexing cam mechanism, reduce the noise, and prolong the service life.

Another technical problem to be solved by the present invention is to simultaneously design the processing method of the arcuate indexing cam mechanism. The processing method is a processing tool position control method, including a control method for the linkage between the cam rotation axis z ₁ and the tool rotation axis z ₂ , and is characterized in that the processing method adopts a single-sided four-coordinate linkage processing tool position control method; that is, in the When the above-mentioned cam rotation axis z ₁ and tool rotation axis z ₂ are linked and rotated, the tool also moves linearly along the y ₂ and z ₂ coordinates; the equation of the linear movement is:

y ₂ ＝-y ₁ ＝ΔR·cos β ₀

z ₂ =-z ₁ =ΔR·sin β ₀ , where:

ΔR is the upper edge of the tool 7 at the center of the roller 2 ${\mathrm{\β}}_0=\mathrm{\β}\left(\frac{h}{2}\right)$ The difference between the direction moving tool and the radius of the roller;

H is the width of roller 2;

h₀为设计常数。β ₀ is the contact angle at which the center of the tool 7 is placed on half the width of the roller 2, and its value is specifically

_h0 is a design constant.

Compared with the traditional processing method, the processing method of the arc-shaped indexing cam mechanism of the present invention adopts a single-sided four-coordinate linkage processing tool position control method; that is, the traditional cam rotation axis z ₁ and tool rotation axis z ₂ are rotated in conjunction At the same time as the work, a four-coordinate linkage machining tool position control method is designed in which the tool also moves along the y ₂ and z ₂ coordinates in a straight line. Due to the use of small tools, this design method can realize the required single-side machining, reduce the damage of the workpiece to the tool, prolong the life of the tool, expand the range of tool use, and improve the machining accuracy and work efficiency.

Description of drawings

Fig. 1 is a kind of embodiment schematic diagram of the cooperating structure of the concave curved surface of the convex profile surface and the convex curved surface of the drum type roller of the arcuate indexing cam mechanism of the present invention;

Fig. 2 is a schematic cross-sectional view of an embodiment of the cooperating structure between the concave curved surface of the convex profile surface and the convex curved surface of the drum-shaped roller of the arcuate indexing cam mechanism of the present invention;

Fig. 3 is a schematic diagram of the meshing state of the cam 1 and the roller 2 of the arcuate indexing cam mechanism;

Fig. 4 is a schematic diagram of a point-to-point machining principle for machining a tool and a cam profile;

Fig. 5 is a schematic diagram of a machining tool position control method for traditional two-coordinate linkage work;

Fig. 6 is the mutual position schematic diagram of theoretical contact curve and actual contact curve;

Fig. 7 is a schematic diagram of the processing principle of the planetary grinding mechanism;

Fig. 8 is a schematic diagram of the principle of single-side machining tool position control in the machining method of the present invention;

Fig. 9 is a schematic diagram of the control principle of the single-side machining tool position of the machining method of the present invention;

Fig. 10 is a schematic diagram of the modified positions of the cam profile 4 by the arcuate indexing cam mechanism of the present invention.

Detailed ways

Further describe the present invention below in conjunction with embodiment and accompanying drawing thereof:

A kind of arc surface indexing cam mechanism designed by the present invention comprises a cam and a roller (i.e. follower) 2 engaged with it, and the cam profile 4 includes a positioning section, a transition section and an indexing section, and the cam profile The transition section and indexing section of the surface 4 are concave surfaces, and the matching roller 2 engaged with it is a drum-shaped roller 3 whose curvature radius is smaller than the curvature radius of the concave surface of the convex profile surface 4 (see Figures 1, 2, 3 and 4) .

This design of the present invention is based on the result of in-depth research on the theoretical engagement contact line of traditional or conventional arcuate indexing cam mechanisms: the cam 1 and roller 2 theoretical engagement contact lines of traditional or conventional arcuate indexing cam mechanisms are a space Curve (see Figure 3, 5, 6). The stress distribution in the contact area is relatively uniform, but this ideal state is not easy to achieve in practice. The reasons are: 1. The meshing of this mechanism is a line contact, which is very sensitive to errors; 2. During the processing and assembly process, the cam body and the driven plate may cause linear or angular errors due to various or certain reasons. The result will have a serious impact on the actual contact state between the cam and the roller, so that the original ideal line contact becomes the point contact or line contact on the edge of the actual roller 2 at the same time or alternately, and the motion state is unstable. However, when the roller 2 is in contact with the edge of the cam, the roller 2 will cause a large contact stress, which will deteriorate the lubrication state between the two components. In fact, the roller 2 does not roll at this time, but passively "swipes" on the cam profile 4 in a "shuffle" or "stagnation". This "scratching" is very easy to scratch the cam profile 4 . This poor contact state will greatly shorten the service life of both the cam and the roller, and also make the dynamic performance of the cam mechanism worse.

The research also shows that, no matter from the theoretical analysis or in the actual movement, the conventional curved surface indexing cam mechanism reflects the characteristics that both sides of the cam groove are in contact with the rollers, that is, during the meshing process, the roller 2 must be in contact with the rollers. The inner and outer contours of the cam with _r1 and _r2 as the radius are in contact at the same time, that is to say, the roller 2 slides periodically in the two sides of the cam groove. This contact state is bad. Such sliding will wear both cam 1 and roller 2 very quickly. Through the analysis of the meshing working characteristics of the arcuate indexing cam mechanism, it can be known that the roller 2 and the cam profile 4 actually only need to contact on one side or one side to ensure the transmission and positioning accuracy. Therefore, the cam profile 4 can be The non-contact area is modified and thinned; moreover, due to the existence of various errors during processing and assembly, the cam profile 4 must be repaired before assembly. Therefore, the realization of the single-side machining of the arcuate indexing cam profile 4 is the key to solving the problem.

Accordingly, the main feature of the arcuate indexing cam mechanism of the present invention is that the mn section, the c'e section and the fg section in the 4 transition sections of the cam profile and the indexing section are thinned by 0.02- 0.04mm (see Figure 10). This means that the ab section and the c'd section in the transition section of the cam profile 4 and the index section are not modified; or the mn section and the eh section in the transition section of the cam profile 4 and the index section are along The normal side is thinned by 0.02-0.04mm, and the remaining segments ab, ef and dg are not modified. The former is suitable for low-speed cam mechanism design, and the latter is suitable for high-speed cam mechanism design. But whether it is a low-speed cam mechanism or a high-speed cam mechanism, its machining accuracy and transition section smoothness must be guaranteed.

The principle of this design is: in the case of low-speed movement, the inertial force of the driven plate is smaller than the frictional resistance, and it is only necessary to accurately ensure the accuracy of the ab and cd sections, and the remaining sections are thinned and modified to reduce the thickness. The amount is 0.02-0.04mm. However, in order to ensure a certain degree of coincidence between the roller 2 and the cam surface 4, the c point can be extended to the c' point, that is, the c'e section is thinned and modified, and the c'd section is not thinned and modified. shape processing. The distance from the c point to the c' point or the length of the cc' segment is 1/4-1/5 of the length of the ce segment. In the case of high-speed movement, the inertia force of the driven plate is greater than the working resistance. In order to maintain a good dynamic performance of the mechanism and prevent the occurrence of traverse impact, the roller 2 should try not to contact the cam surface 4 when it is in the middle groove. Under the premise of ensuring a certain coincidence degree, the accuracy of ab, ef and dg sections must be guaranteed, and the other sections are modified and thinned. The thinning amount is also 0.02-0.04mm. It should be noted that no matter what the working conditions are, the accuracy of the positioning section must be accurately guaranteed, and the transition section should be smooth.

The curved surface indexing cam mechanism is a space surface transmission of line meshing. During the movement, the theoretical contact line between the cam and the roller is a space curve. Because the relative speed of each point on the contact line is not equal, it causes uneven wear of the cam and roller; at the same time, because the linear contact transmission mechanism is sensitive to errors, Make the theoretical line contact alternately or simultaneously between line contact, point contact and edge contact in the actual transmission process, the movement is unstable, and the wear, vibration and noise are aggravated, resulting in a service life much lower than its design life, positioning and The indexing accuracy is reduced, and the excellent performance of theory cannot be fully exerted in practical application.

The present invention proposes the design idea of a new arc-shaped indexing mechanism for point meshing pure rolling pair transmission, that is, on the basis of single-side processing technology for arc-shaped indexing cam, it can absorb the transmission error of the drum-shaped roller follower The advantages of strong inclusiveness, combined with the precise modification technology of the convex contour surface,

According to the principle of single-side machining, at any position, the actual contact line between the tool and the cam and the theoretical contact line between the roller and the cam are tangent at half the width of the roller. At this point, the normal error Δn=0, and the error at both ends of the tool is the largest. . The error distribution of the profile surface after machining has certain rules, that is to say, at other positions except the positioning section, the convex profile surface is concave.

According to the form of the processed profile, if the drum-shaped roller is used to replace the designed cylindrical roller during assembly, the convex surface of the drum-shaped roller and the concave surface of the convex profile are meshed and driven, and the convex profile adopts the above-mentioned The advanced profile modification technology forms a pure rolling transmission form of one-sided point contact, which greatly improves the tolerance of the mechanism to errors. At the same time, the contact form of the convex and concave curved surfaces is conducive to the formation of a dynamic lubricating oil film, and it also has an obvious effect on improving the lubrication state between the two meshing curved surfaces.

This theoretical point contact, under the action of external load and pre-tightening force, will become a small elliptical area contact, which reduces the contact stress. According to the curvature of the cam surface after processing, the curvature of the roller can be selected accordingly to achieve the best meshing state. But the maximum radius of drum roller 3 should be equal to the radius of designed roller 2. The principle of single-side processing makes the error of the positioning section zero, which is conducive to ensuring the positioning accuracy of the mechanism. Combined with the profile modification technology, the sliding pair of the original mechanism line contact becomes the rolling pair of point contact. Experiments show that the transmission efficiency and service life of the cam mechanism of the present invention can be improved to varying degrees, and the movement noise is reduced.

The processing method of the present invention is a processing tool position control method, including a cam rotation axis z ₁ and a tool rotation axis z ₂ linkage rotation control method, and is characterized in that the processing method adopts a single-side four-coordinate linkage processing tool position control method ( Referring to Fig. 8, 9); That is to say, while the cam rotation axis _z1 and the tool rotation axis _z2 are jointly rotated, the tool also moves linearly along the _y2 and _z2 coordinates; the equation of the linear movement is :

y ₂ ＝-y ₁ ＝ΔR·cos β ₀

z ₂ =-z ₁ =ΔR·sin β ₀ , where:

ΔR is the upper edge of the tool 7 at the center of the roller 2 ${\mathrm{\β}}_0=\mathrm{\β}\left(\frac{h}{2}\right)$ The difference between the direction moving tool and the radius of the roller;

H is the width of roller 2;

h₀为设计常数。β ₀ is the contact angle at which the center of the tool 7 is placed on half the width of the roller 2, and its value is specifically

_h0 is a design constant.

This tool position control method makes the tool control direction fixed and the error distribution regular, the control process is simple, and it is also conducive to the improvement of the mechanism structure.

接触线为直线，凸轮廓面4为法向直廓，按单侧面加工刀位控制原理，定位段的法向误差Δn＝0。in the positioning segment

The contact line is a straight line, and the convex profile surface 4 is a normal straight profile. According to the single-side machining tool position control principle, the normal error Δn of the positioning section is 0.

Experiments show that the processing method of the present invention has strong adaptability to cutting tools, little damage, long service life, good processing technology, and can improve processing accuracy and efficiency at the same time.

Claims (2)

1. An arc indexing cam mechanism, comprising a cam (1) and a matching roller (2) engaged with it, the cam profile (4) comprising a positioning section, a transition section and an indexing section, and the cam profile The transition section and indexing section of (4) are concave, and the roller (2) is a drum-shaped roller (3) whose curvature radius is smaller than that of the concave surface of the convex profile (4), and is characterized in that the convex In the transition section and indexing section of the profile surface (4), the mn section, c'e section and fg section shown in Figure 10 are thinned by 0.02-0.04mm along their normal direction; or the convex profile surface (4) In the transition section and indexing section, the mn section and eh section shown in Figure 10 are thinned by 0.02-0.04mm along their normal direction. 2. A processing method of an arcuate indexing cam mechanism according to claim 1, the processing method is a processing tool position control method, comprising a cam rotation axis z ₁ and a tool rotation axis z ₂ linkage work control method, characterized in that This processing method adopts a single-sided four-coordinates linkage processing tool position control method; that is, while the cam rotation axis _z1 and the tool rotation axis _z2 are working in conjunction with each other, the tool also moves linearly along the _y2 and _z2 coordinates work; the equation of the linear movement is: y ₂ =-y ₁ =ΔR·cosβ ₀ z ₂ =-z ₁ =ΔR·sinβ ₀ , where: ΔR is the upper edge of the tool 7 at the center of the roller 2 ${\mathrm{\β}}_0=\mathrm{\β}\left(\frac{h}{2}\right)$ The difference between the direction moving tool and the radius of the roller; H is the width of roller 2; β ₀ is the contact angle at which the center of the tool 7 is placed on half the width of the roller 2, and its value is specifically

_h0 is a design constant.

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