NO141336B - GRINDING MACHINE. - Google Patents

Abstract

Grinding machine.

Description

When manufacturing construction elements, such as e.g. metal machine parts, it is often necessary for the elements to have a machined surface in a special design and shape. Thus, e.g. machine elements that must interact with each other, sliding elements, gears, and e.g. chambers, have mating surfaces that have a precise shape. In those cases where these surfaces are straight, circular or have another regular shape, the machining of the surface does not present particular difficulties. When, on the other hand, the desired surface follows a complicated curve, e.g. that the degree of curvature constantly changes, machining becomes both difficult and expensive.

If the surface is an outer surface, it can be used

a lathe or similar machine. If you do not work

If you have critical tolerances, you can use a milling cutter. A milling cutter is advantageous because it can be used to process both the external and internal surfaces of a workpiece.

When working with critical tolerances, a grinding machine is usually used. Grinding machines can produce very precise surfaces. If the surfaces are complicated in shape, the expenses in connection with the acquisition of the grinding machine will often be so great that such a method prohibits itself. For example, it may be necessary to have several separate grindings in order to be able to produce a particularly complex surface, and each grinding operation requires the workpiece to be fed through a separate grinding machine. With today's available grinding machines, it is difficult to control the feeding of the workpiece relative to the grinding wheel,

both with regard to direction of movement and speed past the grinding wheel. Grinding wheels of different sizes also require that the workpiece must be fed through different paths in order to

could produce the same surface. The grinding wheels are also worn during grinding, and therefore an adjustment or readjustment must be made to obtain the desired surface. This applies in particular when it comes to the production of curved surfaces. In addition to the problems encountered when working with different sized grinding wheels, one also has the problem that any change in the feed rate of the workpiece relative to the grinding wheel will have a . impact both on the efficiency of the grinding and on the quality of the finished surface. Different grinding speeds will produce different surface qualities. This therefore requires further processing of the workpiece, so that you can get exactly the same conditions over the entire surface.

According to the invention, the aim is to provide a grinding machine which can be used for grinding very precise dimensions both when it comes to external and internal surfaces. The new grinding machine should thus be particularly well suited for grinding internal surfaces, such as, for example, the internal walls of the stator part of a Wankel engine.

The curved walls in the housing of the Wankel engine are mostly elliptical, but since they are not the same ellipses, one encounters very great difficulties when it turns. about getting an economic production in a production line. Several times of grinding and polishing are required to obtain an acceptable result. Without precise grinding and polishing, wear will quickly occur due to the interaction with the rotor. The motor will also be affected in a negative direction as such when the rotor has a poor match with the stator.

These disadvantages, which become noticeable during manufacture and when it comes to maintenance of the engine, have been a hindering factor when it comes to the introduction of this type of engine in mass-produced cars. However, the Wankel engine has great potential advantages. It is simple, compact and equally powerful. When the wall of the stator is precisely machined, the motor will have a great working efficiency. It is also of significant importance that Wankel engines are believed to offer great opportunities when it comes to reducing the amount of harmful exhaust gases. However, in order to achieve the advantages that the Wankel engine potentially has, it is absolutely necessary that the wall surface in the stator is machined very precisely, and for economic reasons it is also a requirement that it must be able to be produced in a mass production line in an economical way.

The new grinding machine includes a ring-shaped cam element where one surface is identical to the surface of the workpiece to be ground. Is e.g. workpiece the stator in a Wankel engine, the inner surface of the cam element is polished to a contour identical to the inner wall of the stator. The workpiece is clamped relative to the cam element for movement in a path that conforms to the contour surface of the cam element. A grinding wheel acts on the surface of the workpiece while the workpiece is fed along the desired path. In order to move the workpiece through the desired path, a drive cam follower is arranged which rests against the contour surface of the cam element and causes a movement of the cam element when the drive cam follower is rotated.

The axis of rotation of the drive cam follower is held

in a plane that runs perpendicular to the surface of the comb element. The grinding wheel is also mounted with the axis of rotation arranged in it

this plane and is pressed in this plane against the surface of the workpiece to be ground. With a rotation of the drive wheel at a constant speed, the cam surface will be fed at a constant speed past the point of attack of the drive cam follower. Thereby, the surface of the workpiece to be ground is moved past the grinding wheel at a constant speed, and material is thus removed at a constant speed during grinding. As a result of the grinding wheel being mounted so that its axis of rotation lies in a plane perpendicular to the surface to be ground, wear and tear of the grinding surface with an accompanying reduction in the diameter of the grinding wheel will not affect the grinding. You can even use grinding discs with different diameters without this affecting the grinding and without thereby deviating from the assumed contour.

From US patent no. 3 435 563 a grinding machine is known, for example for grinding triangular ventilation windows. In this known construction, a cam-cam follower system is used which aims to maintain the angle of attack of the grinding disc against the glass. You will not be able to continuously maintain a specific relationship between the cam surface and the cam follower and the grinding wheel and the workpiece. In particular, it applies that at every place where the surface of the guide rail has an edge in the radius of curvature, the cam follower star will not be able to hold the cam and the follower at right angles to each other.

As a result of the fact that the steering wheel and the subject revolve around a fixed

axis, the speed of movement past the cam follower and the grinding wheel will not be constant either.

It is known from US patent 2,421,548

a grinding machine, where precision grinding of the workpiece cannot be achieved. The feeding of a cam around a ring-like follower will, as a result of the used drive roller having contact with the outer surface, tend to cause a rolling of the follower about the used conical head. You will not be able to grind a surface that exactly corresponds to the cam surface.

From US patent no. 2 836 936, a grinding machine is also known where two cam surfaces are used which interact with respective elements. The contact position between the elements and the combs can change during grinding, and there is therefore no guarantee that this contact interaction will always be maintained in a specific plane normal to the surface at the contact point. As a result, different parts of the cam rafts will move past the interacting elements at different speeds during the rotation. This again means that the workpiece will move past the grinding wheel at varying speeds, and the result is uneven grinding.

From the Austrian patent document no. 169 839 it is known to use two separate control curves which cooperate with transmission links so that one can thereby control the movement of a grinding wheel so that one obtains the desired perpendicular relationship. However, it is a condition that you have synchronous operation between the workpiece and the cam discs.

The aim of the present invention is to provide a grinding machine which provides uniform grinding at any point on the surface of the workpiece. This is achieved by using a new cam-cam follower system in combination with a grinding device. In the cam-cam follower system, there is a cam whose radius of curvature changes. A cam follower rests against the cam surface in a specific plane normal to the cam surface. This normal or vertical position is continuously maintained as the cam surface moves through the contact point. In this way, all parts of the cam surface will be moved through the point while maintaining the right-angled relationship.

A grinding wheel has its center of rotation fixed in the same plane above the cam follower. The workpiece is fixed in relation to the cam. In this way, a movement of the cam in relation to the cam follower will result in an identical movement of the workpiece in relation to the grinding wheel. By maintaining the aforementioned right-angled relationship in the determined plane and by moving the cam at a constant speed, all parts of the cam surface will be moved relative to the cam follower at a constant speed in a place that does not move during grinding. Due to the fixed relationship between the grinding wheel and cam follower and the workpiece and comb, the grinding wheel will affect the workpiece at a point directly above the point where the cam follower interacts with the cam. The point will not move during grinding. Thus, when the cam surface is moved at a constant speed in relation to the cam follower, the surface of the workpiece will move at a constant speed in relation to the grinding wheel. If the grinding wheel rotates at a constant speed, all parts of the work piece will be ground at a constant speed, as both the surface of the work piece and the grinding wheel move at constant speeds through the contact point. You thus achieve uniform grinding at every place on the work piece.

According to the invention, there is thus provided a grinding machine including a comb with a changeable radius of curvature, a comb follower for cooperation with the comb surface, a holder for holding the comb surface against the comb follower, a retainer for holding the workpiece in relation to the comb, a grinding device for grinding the workpiece and a carrier for storing the grinding device for movement towards and from the workpiece, and what characterizes the grinding machine according to the invention is that the cam follower is a drive cam follower that drives the cam,

that the holder is arranged to keep the drive cam follower's attack plane at right angles to the cam surface at all times, and that the grinding device is stored for movement towards and from the workpiece in a plane perpendicular to the workpiece's surface, which plane is fixed in relation to the drive cam follower's attack plane.

Additional features of the grinding machine according to the invention will be apparent from the subclaims. In a subsequent description of some exemplary embodiments, the advantages of the invention will be explained in more detail.

The invention will now be described in more detail with reference to the drawings where

fig. 1 shows a schematic section through a grinding machine according to the invention,

fig. 2 shows a schematic view of the cam and drive cam follower,

fig. 3 shows a section through the grinding machine along the line 3 - 3 in fig. 2,

fig. 4 shows a section through the grinding machine along the line 4 - 4 in fig. 2,

fig. 5 shows a section along the line 5 - 5 in fig. 4,

fig. 6 shows a schematic view of the cam and the drive cam follower in an alternative embodiment,

fig. 7 shows a section through an alternative embodiment of the grinding machine along line 7 - 7 in fig. 6,

fig. 8 shows a section through an alternative embodiment of the grinding machine along the line 8 - 8 in fig. 6.

As shown in fig. 1, the grinding machine includes an annular cam element 1. A drive cam follower 2 abuts against the inner surface 3 of the cam element, and a guide roller device 4 abuts against the outer surface of the cam and presses the cam into contact with the drive cam follower 2. The cam element is mounted at one end on a support device 6 which at the other end is designed for holding the work piece 7. A grinding wheel 8 rests against the inner surface 9 of the work piece. In order for the comb to be able to move in a path corresponding to a surface 3, the support device 6 is mounted in a bearing 10. A movement of the comb element results in a similar movement of the workpiece past the grinding wheel.

In the particular design example shown here, the cam element 1 is made with an internal surface 3 that corresponds to the curved wall surface that is desired in the stator of a Wankel engine. This form is shown in fig. 2. The drive cam follower 2 rests against the inner surface of the cam element at point 11. At this point, the drive cam follower and the inner surface of the cam are tangentially arranged relative to each other. The tangent is drawn with the line T. A plane P-l extends at right angles to the tangent and through point 11. This plane also extends at right angles to surface 3 at point 11.

The drive cam follower 2 is mounted so that its axis of rotation 12 lies in the plane P-1. The guide roller device 4 includes two follower rollers 13 and 14. These rollers have rotation axes arranged in a plane P-2 which runs perpendicular to the plane P-1. The follower roller device is pressed against the cam and provides a resultant force which lies in the plane P-1 and passes through the point 11.

The outer surface of the comb element includes

upper and lower cam sections 15 and 16 which cooperate with the follower roller 13 and 14 respectively. The follower rollers are mounted in a slider 17. The slider is stored in a housing 18 which is attached to the machine foundation 19. The slider 17 is spring-loaded by means of a spring 20 which pushes the slider towards point 11 in the plane P-l. Thereby the follower rollers 13 and 14 are pressed against the respective cam sections 15 and 16 and thereby hold the cam element against the drive cam follower 2.

As can be seen from Fig. 2, the two cam sections or cam grooves on the cam element are made with different contours. The exact contour of each comb groove is determined by the surface 3. Along the sides it is seen that the comb grooves undercut each other beyond the parts of the inner surface 3 which have a convex shape. The difference in contour is due to the fact that a pair of guide rollers are used instead of a single guide roller. When using a pair of follower rollers, they will come into contact with various peripheral points on the cam grooves during the movement of the cam element.

When it comes to grinding the stator wall in a Wankel engine, the wall or surface to be ground will have a constantly changing radius of curvature. Because the follower rollers are offset from one another, the cam grooves will have different shapes over the entire periphery. However, the difference is small and is therefore, with the exception of the clearly underlined sections, not shown in fig. 2.

The support device, which carries the comb element, includes a spindle 21. On the lower end of the spindle is attached a carrier -22 to which the comb element is bolted. On the upper spindle end is another carrier 23 to which the workpiece 7 is attached. The spindle can rotate about its longitudinal axis and can also move laterally during this rotational movement, in a path determined by the internal surface 3 of the cam element. To enable this, the spindle is provided around the middle with a circular bearing plate 24 whose peripheral part is arranged inside a housing 25. The housing is made with several upper and lower pockets 26 and 27 which are open to the sides of the bearing plate.

The pockets are supplied with compressed air which acts against the bearing plate in the housing 25. The pockets can be dimensioned and/or the air pressure can be regulated to achieve a compensation of the spindle weight and associated parts, so that a floating storage is achieved. Alternatively, a hydraulic pressure can also be used. You can also proceed in such a way that air pressure is supplied to the underside of the bearing plate while oil is supplied to the upper side of the bearing plate, so that bearing lubrication is enabled here. In all cases, a bearing effect is achieved which enables rotation of the spindle and a lateral movement of the spindle in a plane perpendicular to the axis of rotation. This lateral and rotational movement is made possible with minimal friction.

When the workpiece is to be moved past the grinding wheel to enable grinding of the workpiece, the cam element is inserted between the drive cam follower and the follower rollers, so that the inner surface 3 of the cam element can be made to move through point 11. To enable this, the drive cam follower is stored on the end of a shaft 28 which is stored in a housing 29. The other end of the shaft is provided with a disc 30

for a drive belt 31. The drive belt is placed around a disc 32 on the shaft 33 of a drive motor 34. A constant speed motor is used, so that a constant rotational speed is obtained for the drive cam follower.

When the drive cam follower rotates, it will affect the inner surface of the cam element, and the cam element will therefore move. The guide rollers rest on the outside of the cam element and hold the cam element relative to the drive cam follower, so that point 11 remains fixed. The inner surface of the cam element will always lie along the tangent T at point 11 and thus be perpendicular to the plane P-1. With a constant rotational speed of the drive cam follower 8, the surface 3 will be fed through the point 11 at a constant speed.

The use of a pair of guide rollers arranged on either side of the plane P-1 effectively overcomes inertial forces which attempt to cause the cam element to rotate around the drive cam follower and thus displace the point 11 out of the plane P-1. You can use a single guide roller whose axis of rotation then lies in the plane P-l. This design will be described in more detail below. However, a single follower roller will require significantly greater force to overcome the cam member's tendency to rotate around the cam follower.

The grinding wheel 8 is mounted with the axis of rotation in the plane P-1. While the drive cam follower's axis of rotation is fixed in the plane P-1, the grinding wheel can move freely in this plane towards and from the surface 9 of the workpiece.

The grinding wheel is together with the drive motor 35 mounted on a carriage 36. A guide screw 37 runs parallel to the plane P-1 and passes through a nut 38 which is attached to the carriage. A stepper motor 39 is arranged for turning the guide screw. A turn of the guide screw will cause a movement of the slide and thereby also a movement of the grinding wheel in the plane P-1.

When the grinding wheel's rotation axis is fixed for movement in the plane P-1, a change in the size of the grinding wheel or a wear of the grinding surface will not affect the grinding. This is most clearly shown in Fig. 2, where grinding wheels with different diameters are indicated by dashed lines. Their point of attack on the workpiece will always correspond to point 11 where the drive cam follower rests against the inner surface of the cam element. As can be seen from fig. 2, the size of the grinding wheel will not change the shape of the surface being ground. This is because the surface will always lie perpendicular to the plane P-l at point 11.

Because the workpiece is fixed relative to the cam element, a movement of the cam surface 3 through the point 11 at a constant speed will result in the workpiece passing the grinding wheel at a constant speed. This ensures that the surface of the workpiece will always have an even surface finish. The constant feed rate also provides a more efficient grinding

and less wear on the grinding wheel.

During the grinding of the inner surface of the workpiece, the grinding disc is advantageously moved up and down. For this purpose, a vertically movable carriage 40 is arranged which connects the grinding wheel to the carriage 36. The carriage 40 can move vertically along the carriage 36 under the influence of a cam follower mechanism which is shown in fig. 3. The sled 40 is provided with a follower roller 41 which rests against a cam 42. The cam 42 is attached to the end of the shaft of a motor 43. When this shaft rotates, the cam 42 will rotate. The cam surface is given such a shape, e.g. elliptical shape, that the slide 40 gets the desired upward and downward movement.

Mounting the grinding wheel on a vertical slide is also advantageous because it enables the grinding wheel to be lifted so that it is easier to mount and dismount the workpiece on the carrier 23. For lifting the slide upwards, a hydraulic working cylinder 44 is arranged.

When the grinding machine is to be used, the desired cam element is attached to the carrier 22. With the grinding disc in the raised position, the workpiece is then attached to the carrier 23. The grinding disc is then lowered into the workpiece. A pivoting movement or rotation of the drive cam follower causes a movement of the cam member in a path corresponding to its contour surface. A similar movement of the workpiece is provided, and the stepping motor 39 is used to feed the grinding wheel into the workpiece. The surface of the workpiece is sanded, with the stepper motor being used to regulate the amount of sanding for each pass of the workpiece, until the finished surface corresponds to the cam surface of the cam element.

As can be seen from fig. 6-8, a single guide roller can be used in the sanding machine which rests against the outer surface of the cam element. The construction shown in fig. 7 and 8 largely correspond to the construction in fig. 3 and 4, with the exception of the cam follower arrangement. The same reference number as in fig. is therefore used for corresponding parts. 3 and 4, with the addition of the sign '.

When only a single guide roller 45 is used, the outer surface of the cam 1 has a single cam groove or cam section 46. The surface in the cam groove will always run parallel to the inner surface 3 of the cam. Otherwise, there is the same relationship between the drive cam follower, the cam and the guide roller as in fig. 2. That is, the drive cam follower 2 has its axis of rotation in the plane P-l which is perpendicular to the tangent through the point 11 where the drive cam follower interacts with the inner surface of the cam 1. The rotation axis of the roller 45 also lies

in the plane P-1, and the roller is pressed against the cam and produces a resultant force which lies in this plane and passes through point 11. The mechanism which presses the roller 45 against the cam is shown in fig. 8, and it can be seen that it is the same mechanism used in the embodiment in fig. 4.

The invention has been described above in connection with the grinding of internal surfaces, but the invention can naturally just as well be used for grinding external surfaces. In this case, the cam element is provided with an external surface that corresponds to the desired surface to be ground on the workpiece. The drive cam follower then rests against the outer surface of the cam element, while the guide roller or rollers move along the inner surface.

Claims (13)

1. Grinding machine including a cam (3) with variable radius of curvature, a cam follower (2) for cooperation with the cam surface, a holder (4) for holding the cam surface (3) against the cam follower (2), a retainer (6) for holding of the workpiece (7) in relation to the cam (3), a grinding device (8) for grinding the workpiece (7) and a carrier (36) for storing the grinding device (8) for movement towards and from the workpiece (7), characterized by that the cam follower (2) is a drive cam follower that drives the cam (3), that the holder (4) is designed to keep the drive cam follower (2)'s plane of attack (P-l) at right angles to the cam surface (3), and at that the grinding device is stored for movement towards and from the workpiece in a plane perpendicular to the surface of the workpiece, which plane is fixed in relation to the attack plane (P-l) of the drive cam follower (2). 2. Grinding machine according to claim 1, character- in particular in that the grinding device (8) includes a grinding disc which is mounted for rotation about an axis which lies in the aforementioned specific plane. 3. Grinding machine according to claim 1, characterized in that the cam (3) is an annular body with an inner and outer cam surface, the cam follower (2) rests against one surface, and the holder (4) rests against the other surface. 4. Grinding machine according to claim 2, characterized in that the inner surface of the cam (3) is shape-matched to the surface to be ground on the workpiece. 5. Grinding machine according to claim 3 or 4, characterized in that the holder (4) includes rollers (13, 14) and that the cam follower (2) includes a wheel that rests against the cam (3) in a single, fixed place, with its axis of rotation located in a specific plane that runs perpendicular to the cam surface at the mentioned location, and that the second surface of the cam (3) includes two separate track sections which each interact with a roller (13, 14) in the holder (4). 6. Grinding machine according to claim 5, characterized in that the said rollers (13, 14) are rotatably mounted with the axes of rotation arranged in a common plane (P-2) which runs perpendicular to the said specific plane (P-1). 7. Grinding machine according to claim 6, characterized in that the rotation axes of the rollers (13, 14) are arranged symmetrically in relation to the aforementioned specific plane (P-1). 8. Grinding machine according to claim 2, characterized in that the said surface of the cam (3) includes a single track section, and that the holder (4) includes a single follower wheel which cooperates with the track section. 9. Grinding machine according to claim 8, characterized in that said guide wheel is rotatably mounted with its axis of rotation located in said specific plane (P-1). 10. Grinding machine according to claim 9, characterized in that the groove section runs parallel to the inner surface of the comb. 11. Grinding machine according to one of the preceding claims, characterized in that the retainer (6) for holding the workpiece (7) in relation to the cam (3) includes a spindle whose axis of rotation lies parallel to the aforementioned specific plane (P-1), which spindle has a first support device (22) at one end for supporting the cam (3), and a second support device (23) at its other end for supporting the workpiece (7), in which the spindle is supported for rotation about its axis and for movement in a direction perpendicular to the axis. 12. Grinding machine according to claim 11, characterized in that the storage includes a bearing plate (24) which is attached to the spindle and extends perpendicular to it, a bearing housing (25) which occupies and carries a peripheral part of the bearing plate (24), as well as fluid devices for storage of the plate in the housing for rotational movement and lateral movement, the plate being held against axial movement. 13. Grinding machine according to claim 12, characterized in that the housing (25) faces the two end sides of the plate (24), and that the fluid arrangement includes a pneumatic device which acts against one side of the plate and presses the plate in an axial direction of the spindle , while a liquid lubricant supports the other side of the plate against the adjacent housing surface.