Patent Application
20100317259
The present disclosure relates to a surface grinder.
For surface grinders, a workpiece holder is used to bring the workpiece held on a workpiece holder into engagement with at least one grinding tool. It is necessary in this respect to be able to fix the workpiece with high precision on the workpiece holder, so that when the workpiece is introduced into the machining area of the grinding tool, the workpiece holder and the grinding tool do not tilt with respect to one another. A correspondingly careful matching is necessary in the area of a workpiece exit from the machining area, in order to avoid tilting between the workpiece, the workpiece holder, the grinding tool and an outlet guide adjoining the machining area.
A transfer of non-machined workpieces from a loading machine into workpiece receptacles of the workpiece holder is also critical. In this area as well, if all components are not precisely matched, it is possible for a workpiece to become tilted with respect to these components. All of this implies that a surface grinder must be set up extremely carefully to avoid damage to components of the surface grinder and/or workpieces.
Starting from this situation, the present disclosure is based on the problem of preventing damage to a surface grinder.
This problem is solved according to the present disclosure for a surface grinder of the type mentioned above by a clutch device that provides a rotationally fixed connection between the drive unit and the workpiece holder that can be released at a predetermined limit torque.
The surface grinder according to the present disclosure makes it possible to release a rotationally fixed connection between the drive unit and the workpiece holder as a function of a specifiable limit torque. This makes it possible to exert the drive torque necessary for surface-grinding of a workpiece, but with the rotationally fixed connection being released when a limit torque is reached. The consequence is that the drive unit can be decoupled from the workpiece holder and damage to the surface grinder of the type mentioned above can be prevented. As soon as the specifiable limit torque is exceeded, the release of the rotationally fixed connection of the drive unit and the workpiece holder prevents the workpiece holder from being driven further in the direction of rotation in a state where it is tilted with respect to a workpiece and/or other components of a surface grinder.
The surface grinder according to the present disclosure is particularly advantageous if a disk-shaped workpiece holder is used, the overall height of which is at most approximately 1 cm or even only a few millimeters. Such a thin workpiece holder has the advantage of being able to machine very thin workpieces, but it has the disadvantage of the workpiece holder itself having very low distortion resistance. Since the workpiece holders, with a diameter of about 50-100 cm or even more, extend over a very large area in comparison to their thickness, they are particularly susceptible to a deformation based on the tilting of a workpiece holder with respect to a workpiece and/or other parts of the surface grinder.
Due to the separability of the rotationally fixed connection between the workpiece holder and the drive unit, and the accompanying stoppage of the workpiece holder, additional components of the surface grinder can also be protected against damage in the area of a workpiece feeder and a workpiece discharge unit. The same applies to the protection of an optional loading unit by means of which the workpiece holder can be furnished with non-machined workpieces. In this way, a device for measuring the geometry of a machined workpiece that may be present in the vicinity of the workpiece holder can also be protected from damage.
The surface grinder according to the present disclosure also makes it possible to set up the machine with a less of an exacting effort and with higher tolerances.
Within the scope of the present disclosure, it is possible for the specifiable limit torque to be set manually, based on empirical values, for example. It is preferred, however, that a control unit is provided which adjusts the limit torque of the clutch device as a function of an actually occurring maximum drive torque. It is also preferred that the limit torque is set to be higher than the actually occurring maximum drive torque in order to prevent an unintended release of the rotationally fixed connection.
The clutch device in one form is constructed in the form of an electromagnetic clutch. This carries the advantage of being able to adjust the limit torque very precisely.
It is further preferred that the rotationally fixed connection is a frictionally engaged connection. Thereby, the mechanical stress on engaged clutch elements can be reduced.
The surface grinder in one form is constructed as a double surface grinding machine that has two grinding tools, between which a grinding gap is formed in which a workpiece can be machined on opposite workpiece surfaces. The present disclosure further relates to a method for setting up a surface grinder, wherein the surface grinder comprises at least one grinding tool, a workpiece holder for holding at least one workpiece and a drive unit for driving the workpiece holder in a rotational direction.
The present present disclosure is based on the additional problem of creating a method for setting up a surface grinder with which damage to the surface grinder can be prevented.
This problem is solved according to the present disclosure for a method as mentioned above in that the actually occurring maximum drive torque is determined during the grinding of at least one sample workpiece, and in that a rotationally fixed connection that can be released at a limit torque determined as a function of the maximum drive torque is produced between the drive unit and the workpiece holder.
Advantages and various forms of the method according to the present disclosure have in part already been explained above in connection with the advantages and forms of the surface grinder according to the present disclosure. Therefore only those advantages and forms of the method according to the present disclosure will be discussed that were not already explained above in connection with the advantages and forms of the surface grinder according to the present disclosure.
By determining an actually occurring maximum drive torque using at least one sample workpiece, the drive torques occurring during the regular operation of the surface grinder can be determined precisely and simply. The limit torque, which is then to be specified for the regular operation of the surface grinder, is determined as a function of the actually occurring maximum drive torque.
One possibility for determining the actually occurring maximum drive torque is to detect the power requirements of the drive unit. For example, voltage or current values at which the drive unit is operated can be detected.
Additionally or alternatively, it is possible to measure the actually occurring maximum drive torque with a torque measuring device. Such a measurement device is preferably arranged in a spatial connection with the clutch device, for example, between the drive unit and the clutch device or between the clutch device and the workpiece.
It is further preferred if the limit torque is equal to the maximum drive torque multiplied by a factor greater than 1. In this way it can be assured that a slight exceeding of the maximum drive torque measured using the sample workpiece does not lead to an undesired disengagement of the clutch device in the regular operation of the surface grinder.
The limit torque is preferably equal to the maximum drive torque multiplied by a factor of less than roughly 1.5. In particular, the factor is between approximately 1.1 and approximately 1.3. These factors offer a good compromise between an overload protection of the surface grinder components and an operation which is as free of interruption as possible.
It is further preferred that at least one sample workpiece with the same geometry as a non-machined workpiece should be surface-ground by means of the surface grinder. Thereby the actually occurring maximum drive torque can be determined very precisely. In this context, it is advantageous if maximum drive torques determined using sample workpieces, and possibly the associated limit torques are stored, so that these values are already known and can be used after a re-setup of the surface grinder.
The maximum drive torque is advantageously determined when an engagement surface area between the at least one grinding tool and the at least one sample workpiece is at a maximum. In this state of the surface grinder, the friction surfaces between the workpiece and the grinding tool are maximized so that maximum drive torques appear in this state. If a plurality of workpieces is simultaneously machined in the machining area, the maximum drive torque and thus the limit drive torque are increased correspondingly.
In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:
One form of a surface grinder, denoted overall by reference number 10 in
The surface grinder 10 further comprises a disk-shaped workpiece holder 16 which is rotatably drivable about a workpiece holder shaft 18. The workpiece holder shaft 18 and the grinding disk shaft 14 are mutually parallel or are inclined relative to one another by a few degrees, at most 5° for example.
The workpiece holder 16 comprises a plurality of workpiece receptacles 20, which are preferably spaced identically in the radial direction relative to the workpiece holder shaft 18 and are furthermore spaced preferably equally from one another in the circumferential direction.
The workpiece holder 16 comprises at least two, and in particular at least ten workpiece receptacles 20. A workpiece receptacle 20 can be formed, for example, by a hole-shaped recess, which serves to receive a workpiece. A workpiece 22 is shown crosshatched in
The surface grinder 10 has a loading area 24 in which non-machined workpieces 22 can be inserted into a workpiece receptacle 20. The insertion can be done manually or by means of a loading device 26, which in particular has a magazine 28 for storing non-machined workpieces 22.
The surface grinder 10 further comprises a machining area 30 in which workpieces 22 held on workpiece holder 16 are engaged with the upper grinding tool 12 and the lower grinding tool for surface grinding.
The surface grinder 10 further comprises a removal area 32 in which workpieces 22 can be removed from the workpiece receptacles 20.
In the machining area 30, the upper grinding tool 12 and the lower grinding tool are spaced away from one another in such a manner that a grinding gap results in which workpieces 22 are accommodated and supported at the top and the bottom relative to the direction of gravity. Outside the machining area 30, the workpieces 22 are supported in the loading area 24 and in the removal area 32 on their underside with the aid of workpiece rests not shown in the drawing.
The surface grinder 10 comprises a measurement device 34 that is arranged in an entry area of the removal area 32. A thickness of a workpiece 22 parallel to the extension direction of the grinding gap is measured with the aid of the measurement device 34.
Adjoining the machining area 30, the surface grinder 10 has a first guide unit 36 in the vicinity of an inlet to the machining area 30, and a second guide unit in the vicinity of an outlet of the machining area 30. The guide units 36 and 38 each have a plate-shaped guide element 40, 42 which has a guide surface 44, 46, respectively, facing the workpiece holder 60. The guides 44, 46 are each finished with a border 48 or 50 respectively.
Non-machined workpieces 22 can be pressed with the aid of the guide element 40 of the first guide unit 36 downwards relative to the direction of gravity against a workpiece rest (not shown), so that a workpiece can be oriented precisely relative to the direction of gravity between the upper grinding tool 12 and the lower grinding tool. In a corresponding manner, a machined workpiece 22 can be guided out of the machining area 30 with the aid of the guide element 42 of the second guide unit 38.
In the removal area 32, the surface grinder 10 further comprises a workpiece discharge element 52, which is constructed in the form of a slide. Finished machined workpieces 22 held on the workpiece holder 16 can be removed downwards out of the workplace receptacles 20 and discharged via the workpiece discharge element 52.
A drive unit 56, which is embodied, in particular, in the form of an electric motor, is provided for driving the workpiece holder 16 about the workpiece holder axis 18 in the direction of rotation 54.
The drive unit 56 does not act directly on the workpiece holder 16, but rather through the interposition of a clutch device 58. In an engaged state, the clutch device 58 provides a rotationally fixed connection between the drive unit 56 and the workpiece holder 16. The rotationally fixed connection of the clutch device 58 is released as a function of a predetermined limit torque.
The limit torque of the clutch device 58 is controlled using a control unit 60, which preferably also communicates with the drive unit 56 in order to specify an energy requirement of the drive unit 56.
The clutch device 58 is preferably constructed in the form of an electromagnetic clutch 62, which is shown in greater detail in
An input torque of the drive unit 56 is transferred with the aid of an input shaft 64 to a friction liner support 66. The friction liner support 66 has a friction liner receptacle 68 in which, in particular, an annular friction liner 70 is accommodated. The friction liner 70 is movable axially relative to the workpiece holder shaft 18. On its peripheral surface, the friction liner 70 has teeth 72 which create a positively engaged connection in the direction of rotation with matching teeth of the friction liner receptacle 68.
The friction liner 70 can be magnetized, so that it can be attracted by an annular electromagnet 74. The electromagnet 74 is rotationally fixed to an electromagnet holder 16 into which a coil (not shown in detail) is integrated, said coil can be electrically connected with the aid of a terminal 78. When the coil is energized, the electromagnet 74 generates a magnetic field that presses the friction liner 70 against the electromagnet 74, so that a fictional engagement between these partners results. The intensity of the frictional engagement is dependent on the power applied to the electromagnet 74 as specified by means of the control unit 60.
The magnet support 76 is rotationally fixed to an output shaft 80, which is rotatably seated by means of rolling-contact bearings 82 in a stationary housing 84.
The output shaft 80 is rotationally fixed at its end remote from the clutch device 58 to a workpiece support 86. Said end of the output shaft 80 is additionally connected to a bolt 88 that penetrates a central cutout of the workpiece holder 16. This bolt cooperates with a clamping sleeve 90, with which a clamping socket 92 can be pressed down from above onto the workpiece holder 16.
Annular spacer elements 94, which allow an adaptation to different thicknesses of different workpiece holders 16, are arranged between the workpiece holder support 86 and the underside of the workpiece holder 16.
The workpiece holder 16 is rotationally fixed between the spacer elements 94 and the clamping socket 92.
To set up the surface grinder 10 it is possible to use eight sample workpieces, for example, which are brought into the machining area 30 in such a manner that they are simultaneously engaged with the upper grinding tool 12 and the lower grinding tool. A drive torque of the drive unit 56 necessary to transport the sample-grinding tools is correlated with the energy requirement of the drive unit 56. From this, a maximum occurring drive torque can be calculated, which is then multiplied by a factor of, for example, between approximately 1.1 and approximately 1.3. This yields a limit torque which can be adjusted using the control unit 60 on the clutch device 58 by appropriate application of power to the electromagnet 74.
Then non-machined workpieces 22 can be fed to the workpiece holder 16 from the loading device 28 and introduced into the machining area 30. After the machining of the workpieces they are guided out of the machining area 30 by further movement of the workpiece holder 16 in the rotational direction 54, so that they can be removed from the workpiece holder 16 in the removal area 32.
It is possible for the workpiece holder 16 to be operated in steps or to rotate continuously.
If a workpiece 22 becomes tilted during the operation of the surface grinder 10, for example in the vicinity of the outlet of the magazine 28 in the direction towards the workpiece holder 16, or in the vicinity of the border 48 of the first guide unit 36, or in the vicinity of the border 50 of the second guide unit 38, this causes the limit torque to be exceeded, whereby the rotationally fixed connection of the clutch device 8 between the drive unit 56 and the workpiece holder 16 is released by slippage of the friction liner 70 on the electromagnet 74.
The above-described possibility of a tilting of a workpiece 22 is based not only on the fact that parts of the surface grinder 10 may not be set up precisely, but also on the fact that workpieces 22 in the machining area 30 may be lifted up because of the use of coolant, so that they collide with the borders 48, 50 or with a border of the grinding tools.
In an alternative form, not shown in the drawings, the clutch device 58 is arranged relative to the workpiece holder 16, on a side facing away from the drive unit 56, for example, between the clamping sleeve 90 and the clamping socket 92.
This application claims the benefit of provisional application Ser. No. 61/185,845, filed on Jun. 10, 2009, the contents of which are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61185845 | Jun 2009 | US |
