GB2116465A

GB2116465A - Device for grinding flat or spherical surfaces

Info

Publication number: GB2116465A
Application number: GB08307404A
Authority: GB
Inventors: Karl Wieck
Original assignee: GRIESHABER MASCH
Current assignee: GRIESHABER MASCH
Priority date: 1982-03-18
Filing date: 1983-03-17
Publication date: 1983-09-28
Also published as: DE3209982C2; IT1161914B; FR2523496A1; GB8307404D0; IT8320067A0; GB2116465B; DE3209982A1; FR2523496B1

Abstract

A device for grinding flat or spherical surfaces comprising a grinding head (24) and a grinding head holder (12) displaceable relative to each other and mounted on common guideway (14). A grinding spindle (30) is rotatably mounted in the grinding head (24), which has shims (36) and at least one piston rod (80), which is slidable in the grinding head holder (12). The relative movement between the grinding head (24) with the grinding wheel (22) and the grinding head holder (12) is monitored by a sensor (76). When a definable relative movement occurs, clamping devices (40) are actuated, with which shims (36) of the grinding head (24) are clamped, whereby the grinding head (24) and the grinding head holder (12) are braced with each other. Therewith a driving motor (48) is uncoupled from an infeed spindle (52) for the grinding head holder (12) and this is coupled to a device for gradual infeed. The piston rod (80) attached to the grinding head projects into a cylinder (90) of the grinding head holder (12) and carries a piston (86) which is displaceable therein. The piston (86) is acted upon by a pressure medium supplied to the cylinder, which exerts a force on it, which acts in the opposite direction to and at least partly compensates the weight of the grinding head and the grinding wheel together with the tool holder. <IMAGE>

Description

SPECIFICATION Device for the precision grinding of flat or spherical surfaces This invention relates to a device for grinding flat or spherical surfaces by means of a crown- or segment grinding wheel, movable axially towards and away from a workpiece.

In DE-OS No. 2818840 it has been proposed to provide such a grinding device which reacts to a definable relative displacement between a grinding head and a grinding head holder, which has signal transmitters actuatable by guide elements, which are adjustably attached to the grinding head holder, on which clamping devices are provided, which act on the guide elements and clamp the grinding head holder to the grinding head, a coupling being provided, which uncouples the driving motor from an infeed spindle and couples the latter to a device for gradual infeed of the grinding wheel towards the workpiece.

In this previously proposed device, the grinding head hits the workpiece at a rapid traverse rate.

The forces arising between the grinding wheel and the workpiece when the grinding head strikes the workpiece, depend upon the weight of the grinding head and the inertial force produced on braking the grinding head. Since the grinding head is suspended on springs, at the moment of contact between the grinding wheel and the workpiece the springs still make no contribution to the force acting between the grinding wheel and the workpiece. The grinding head is held through the workpiece in an end position, whilst a grinding head holder, constructed as a spindle housing, is still moved in a direction towards the workpiece.

Thereby the spindle housing compresses the springs. Therefore, via the springs, a gradually increasing pressure is exerted onto the grinding head and the workpiece. When a definable pressure is reached, the axial movement of the spindle housing is terminated. Subsequently, the spindle housing is rigidly connected with the grinding head. By a step such as this, the idle time is reduced, because a grinding run is dispensed with, in which the grinding head is moved at a slow speed toward the workpiece.

When grinding workpieces of large dimensions, large grinding wheels and large grinding heads are required. These grinding wheels and grinding heads have bigger weights and larger masses.

Owing to these weights and masses, undesirably greater forces can arise when the grinding wheel strikes the workpiece at high lowering speeds. In fact, the forces arising on the setting of the grinding wheel onto the workpiece can be reduced in a relatively simple manner through a reduction of the lowering speed; however, for as economic a production as possible, a high lowering speed is desired.

It is an object of the invention to provide a grinding device with which high lowering speeds are possible without the production of critical forces on contact of grinding wheel and workpiece, even when the unit consisting of the grinding head and the grinding wheel has large weights and masses.

According to the present invention there is provided a device for grinding flat or spherical surfaces using a crown or segment grinding wheel movable in its axial direction towards and away from a workpiece, comprising a grinding head, a tool holder for said grinding wheel, a rotary grinding spindle attached to the tool holder and mouned in the grinding head so as to be rotatable but not axially movable therein, a grinding head holder, at least one piston connected to the grinding head and slidably mounted in a cylinder arranged on or in the grinding head holder, means for rotating the grinding spindle, means for feeding the grinding head holder and grinding head and thus the grinding wheel towards a location for a workpiece, such means comprising first feed means for fast infeed, uncoupling means for said first feed means, and second feed means for gradual infeed, clamping means operable to clamp the grinding head and the grinding head holder together, sensor means for sensing a relative displacement between the grinding head and the grinding head holder and arranged to operate said clamping means and said uncoupling means thereby to acutate said second feed means, and an inlet to said cylinder adapted for connection to a source of pressure medium for acting on the piston to provide a force which acts in the opposite direction to the weight of the grinding head, the grinding wheel and the tool holder and which at least partially compensates for the weight of the grinding head, the grinding wheel and the tool holder.

On a delay by the unit consisting of the grinding head and the grinding wheel during the setting of the grinding wheel on the workpiece, inertial forces consequently occur and the difference between the weight and the balancing force. The portion originating from the weight can be reduced through a corresponding adjustment of the balancing force to an insignificantly small amount. The total stress between the grinding wheel and the workpiece therefore remains within permissible limits during the delay by the grinding head, despite high lowering speeds. Consequently, even in the processing of large workpieces a very economical mode of operation can be achieved. A further advantage is to be seen in the very simple construction of the grinding head. An axial ball bearing for the grinding head is no longer necessary.Furthermore, the spring pre-tension between the grinding head and the grinding spindle is dispensed with. In a preferred embodiment, provision is made that the cylinder is arranged with its axis parallel to that of the grinding spindle, and that the portion of the cylinder lying below the piston is acted upon by the pressure medium while the portion of the cylinder lying above the piston is open to the surrounding atmosphere. In this arrangement only one of the two cylinder chambers, separated from each other by the piston, it to be connected to the pressure medium. Therefore only one pressure medium duct need be installed to the cylinder. The constructional expense is therefore minimal.

Preferably the cylinder is connected to a supply duct for the pressure medium and an adjustable pressure regulating valve is arranged in this duct.

The pressure regulating valve ensures that a constant pressure prevails in the cylinder chamber which is acted upon by the pressure medium. This pressure is then even maintained when the volume of the cylinder chamber alters.

It is expedient to set the pressure in the cylinder so high that the compressive force counteracting the weight of the grinding head and the grinding wheel together with tool holder, and the inertial force brought about at the beginning of the lowering movement together are smaller than the weight of grinding head, tool holder and grinding wheel. With this step, at the beginning of the downward movement, a relative movement between the grinding head holder and the grinding head is avoided.

Preferably the grinding spindle is mounted in roller bearings arranged close to the ends of the grinding head and is constructed as a hollow shaft with longitudinal grooves or splines, while a drive shaft is attached so as to be longitudinally displaceable in one end in the hollow shaft, and is mounted on a frame of the device and provided with complementary keys. This form of embodiment is distinguished by its simple construction.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawings, which illustrate diagrammatically and by way of example an embodiment thereof, and in which:~ Fig. 1 is a longitudinal section of a device for grinding flat or spherical surfaces, and Fig. 2 is a cross-section along the line I-I of Fig. 1.

Referring now to the drawings, there is shown a grinding device comprising a frame, an upright 10 of which carries guideways 14, along which a grinding head holder 12 is movable, the holder supporting a grinding head 24 which is movable in relation to the holder along the guideways. The guideways 14 extend vertically on the upright 10.

The grinding head holder 12 is composed of a part 16 held between the guideways 14 and two arms 18 projecting one on each side thereof. A driving shaft 46 projects downwardly between the arms 18 and the upper cylindrical end 26 of the shaft is rotatably mounted in the frame upright 10. The lower end of the driving shaft 46 is formed with wedge-shaped longitudinal projections or splines, with which it engages in the interior of a grinding spindle 30 so as to be able to be displaced longitudinally relative to the spindle which is constructed as a hollow shaft with complementary longitudinal grooves. At its lower end, the grinding spindle 30 carries a grinding wheel mounting or tool holder 20 to which a grinding wheel 22 is attached.The grinding spindle 30 is rotatable in the grinding head 24 and is mounted so as to be secured against axial displacement relative to the grinding head. The grinding head 24 is, as already described above, carried in the guideways 14 in the same manner as the grinding head holder 12.

The grinding spindle 30 is centrally arranged in the grinding head 24. Close to the upper end of the grinding head 24, at two positions lying diametrically opposed to each other, there are outwardly protruding projections 32 which are formed with recesses which are not shown in further detail and, in which the ends of vertical shims 36 engage. In Fig. 1 a shim 36 is drawn displaced through 900.

The shims 36 protrude upwardly from the projection 32 and engage in openings 38 of the grinding head holder 12. The grinding head 24 has, as additional guiding means, two axially parallel side plates 34, which are formed with guide tracks not shown in detail, which can slide in the guideways 14. A limit switch or a noncontact sensor 76 is attached to the grinding head holder 12 and monitors the position of the shims 36 vis-a-vis the grinding head holder 12.

Clamping units 40 are provided and have pistons which extend perpendicularly to the openings 38, the pistons can be acted upon by pressure medium so as to come into contact with preferably flattened parts of the shims 36. A belt pulley 42, rotatably mounted on the upright 10, iS driven via a belt 17 by a motor (not shown) and transfers rotational movement via the driving shaft 46 to the grinding spindle 30.

Close to its upper end, the grinding head 24 contains a further projection which extends between the side plates 34. The end of a piston rod 80 is attached to this projection and protrudes upwardly from the grinding head 30 into the part 16 of the grinding head holder 12. The part 16 is formed with a recess, not shown in further detail.

to receive the piston rod 80. Furthermore, the part 16 is formed with a cylindrical chamber 82 which runs axially parallel to the grinding spindle 30. The piston rod 80 which carries a piston 86 projects into the cylindrical chamber 82.

The infeed movement in rapid traverse is effected by a geared motor 48, which by means of a sleeve 50 drives a threaded spindle 52, which is mounted in a nut 54 connected to the grinding head holder 12. A cogwheel 56 is rotatably mounted on the sleeve 50 and meshes with a cogwheel 58, which in turn is firmly connected with a ratchet wheel 60. Also, a rotor 62 of a magneto coupling is slidably mounted on the sleeve 50, and is arranged to revolve between poles 64 carried by the cogwheel 56 and a field generating coil 68. A ratchet engages in the teeth of the ratchet wheel 60 and is actuated by a piston acted upon by pressure medium or by a lifting magnet or similar means, whilst a further ratchet is provided to serve as security against back rotation of the ratchet wheel 60.

The piston rod 80, the lower end of which is expediently screwed into the grinding head 24, carries a piston 86 at its upper end. For the attachment of the piston, the end of the guide column 80 is formed with a thread, onto which two nuts are screwed, and the piston 86, which is formed with a through-bore for the guide column 80, is clamped between the nuts. The piston 86 is sealed against the wall of the cylindrical chamber 82, and is arranged to perform sliding movements, in accordance with the movements of the guide column 80, within the cylindrical chamber 82, which is divided by the piston 86 into an upper chamber 88 and a lower chamber 90. The upper chamber 88 communicates via an opening 92 with the atmosphere, while the lower chamber 90 is connected via an opening, not shown, to a duct 94 through which a pressure medium, e.g.

compressed air, can be fed into the chamber 90.

An adjustable pressure regulating valve 96, shown diagrammatically in the drawing, is arranged in a pressure line leading to the duct 94. The pressure regulating valve 96 ensures that the pressure set, independently of the position of the piston 86 in the cylinder chamber, i.e. independently of the existing volume of the lower chamber 90, is kept constant in the lower chamber. Adjustable pressure regulating valves are commercially available, which enable a precise setting of the pressure produced on the output side and a high degree of control accuracy with a good control stability to the achieved.

When the lower chamber 90 is under the influence of the pressure medium, a compressive force is exerted on the piston 86 urging it upwards. This force is transferred from the piston 86 through the piston rod 80 to the grinding head and thus to the grinding spindle 30 and roller bearings 98 and 100, which are arranged respectively close to the upper and lower ends of the grinding head 24. The grinding spindle 30 is rotatably mounted in the roller bearings 98 and 100 which are secured against axial displacement by means of covers 102 and 104. The covers 102 and 104, which are formed with openings for the grinding spindle 30, seal the upper and lower ends of the grinding head 24.The grinding head 24 together with the roller bearings 98 and 100, the covers 102 and 104, the side plates 34, the guide columns 36 and 80 and the piston 86 form a unit which is-axially displaceable with respect to the grinding head holder 12. The grinding head is understood to mean, accordingly, all those parts, which like the tool holder 20 and the grinding wheel 22 are arranged so as to be axially displaceable with respect to the grinding head holder 12. The force exerted on the piston 86 therefore also affects the grinding head and the parts of the grinding head connected to it. This force has the opposite direction to the force exerted by the weight of the grinding head. By way of an appropriate adjustment of the pressure in the lower chamber 90 the force can be made to compensate for a portion of the weight of the grinding head.

The infeed of the grinding wheel 22 is effected by operating the geared motor 48 to rotate the spindle 52, so that the grinding head and the parts 30,20, 22, 98, 100, 102, 104, 96, 80 and 86 firmly connected thereto, move in a rapid traverse towards the workpiece. When the grinding wheel 22 hits the workpiece (not shown) a force operates between the grinding wheel 22 and the workpiece, which depends upon the delay of the grinding head and parts rigidly connected with it, and the grinding wheel 22, and upon the difference between the weight of grinding wheel and the grinding head and the balancing force brought about by the piston 86. The balancing force is preferably set so high that it counteracts a substantial part of the weight of the grinding head 24 including the parts 30, 20, 98, 100, 102, 104, 36, 80 and 86 and the grinding wheel 22.The stress between the grinding wheel 22 and the workpiece on contact is therefore primarily due to the inertial forces occurring on the delay of the masses. Through the relief of inertial forces, the stresses are considerably reduced. It is therefore possible, even with grinding heads and grinding wheels with large dimensions and correspondingly large masses, to operate the device at a high lowering speed, without the stress on impact of the grinding wheel onto the workpiece becoming unduly great. After the impact of the grinding wheel 22, a relative movement occurs between the grinding head 24 and the grinding head mounting 12, which leads to an increase in volume of the lower cylinder chamber 90. Since the regulating valve 96 keeps the pressure in the chamber 90 constant, the balancing force produced by the piston 86 does not alter.As soon as the shims 36 reach the region monitored by the sensor 76, the sensor 76 emits a signal to a control member, which acts upon the cylinders 40 with a pressure medium and thereby stops the movement of the grinding head 20 in the axial direction with respect to the grinding head holder 12. At the same time the geared motor 48 is stopped and the magneto coupling 62, 64 and 68 is actuated so that now the infeed takes place via the ratchet, the ratchet wheel 60, and the cogwheels 58 and 56, the magneto coupling 62, 64 and 68 and the spindle 52. The actuation of the ratchet can take place at preset time intervals or as a function of the energy input of the driving motor for the grinding spindle. It is also possible to set the infeed by way of a measuring control and to introduce an elasticity balancing process.

At the beginning of the lowering movement, the grinding head 24 together with the parts 30, 20, 98, 100, 102, 104, 36, 80 and 86 and the grinding wheel 22 are accelerated. in order to avoid, at the beginning of the lowering movement, relative movements between the grinding head holder 12 and the grinding head and the parts connected therewith, a pressure is preferably set in the lower chamber 90 at which the compressive force counteracting the weight and the inertial force occurring at the beginning of the lowering movement together are smaller than the weight.

Then even during the acceleration on the grinding head and on the grinding wheel 22 a downward acting force is applied. These parts therefore follow the downward movement of the grinding head holder 12.

The opening 92 of the cylinder chamber 88 to the surrounding atmosphere is preferably constructed as a restrictor. In this way a certain damping is exerted on the movement of the grinding head 24 and of the parts rigidly connected therewith on the impact of the grinding wheel 22 on the workpiece.

A particular advantage of the device described above is to be seen in the mounting of the grinding spindle 30 which is firm against stresses. An axial mounting with great rigidity can be achieved, which contributes to an improvement in the accuracy of the treatment.

Claims

1. A device for grinding flat or spherical surfaces using a crown or segment grinding wheel movable in its axial direction towards and away from a workpiece, comprising a grinding head, a tool holder for said grinding wheel, a rotary grinding spindle attached to the tool holder and mounted in the grinding head so as to be rotatable but not axially movable therein, a grinding head holder, at least one piston connected to the grinding head and slidably mounted in a cylinder arranged on or in the grinding head holder, means for rotating the grinding spindle, means for feeding the grinding head holder and grinding head and thus the grinding wheel towards a location for a workpiece, such means comprising first feed means for fast infeed, uncoupling means for said first feed means, and second feed means for gradual infeed, clamping means operable to clamp the grinding head and the grinding head holder together, sensor means for sensing a relative displacement between the grinding head and the grinding head holder and arranged to operate said clamping means and said uncoupling means thereby to actuate said second feed means, and an inlet to said cylinder adapted for connection to a source of pressure medium for acting on the piston to provide a force which acts in the opposite direction to the weight of the grinding head, the grinding wheel and the tool holder and which at least partially compensates for the weight of the grinding head, the grinding wheel and the tool holder.

2. A device as claimed in Claim 1, wherein the piston is attached to a piston rod connected with the grinding head.

3. A device as claimed in Claim 1 or 2, wherein the cylinder is arranged with its axis parallel to that of the grinding spindle, and wherein the inlet to the cylinder leads into that portion of the cylinder lying beneath the piston to be acted upon by the pressure medium, while the portion of the cylinder lying above the piston is open to the surrounding atmosphere.

4. A device as claimed in Claim 3, wherein the cylinder is open to the surrounding atmosphere through a restrictor.

5. A device as claimed in any one of Claims 1 to 4, wherein the cylinder is connected to a duct for the pressure medium, and wherein an adjustable pressure regulating valve is arrranged in said duct.

6. A device as claimed in Claim 5, wherein the pressure in the cylinder is set so high that the compressive force counteracting the weight of the grinding head, the grinding wheel and the tool holder and the inertias force brought about at the commencement of the infeed movement together are smaller than the weight of grinding head, the grinding wheel and the tool holder.

7. A device as claimed in any one of Claims 1 to 6, wherein the grinding spindle is mounted in roller bearings arranged close to the ends of the grinding head and is constructed as a hollow shaft with longitudinal grooves or splines, and wherein a drive shaft, mounted in a frame of the device and provided with complementary keys, is attached so as to be longitudinally displaceable in one end in the hollow shaft.

8. A device as claimed in any one of Claims 1 to 7, wherein two shims arranged on the grinding head holder at positions diametrically opposed to each other, are clampingly engageable by clamping devices.

9. A device as claimed in Claim 8, wherein both the grinding head holder and the grinding head are carried on a common guideway fixed in the frame of the device, but are movable axially relative to each other, so that a relative displacement of the shims with respect to the clamping devices and the piston rod and piston with respect to the cylinder is made possible.

10. A device for grinding flat or spherical surfaces using a crown or segment grinding wheel movable in its axial direction towards and away from a workpiece substantially as hereinbefore described with reference to the accompanying drawings.