Double-sided grinding machine and method for grinding brake discs

Abstract

The present invention relates to a double-sided grinding machine (10) including a first machine part (16) with a first grinding disc (18) and a second machine part (20) with a second grinding disc (22), the spacing between the first and second grinding discs being adjustable along a machine axis (14), and further including a workpiece holding device (30) for holding a workpiece (26), the workpiece holding device including at least one force sensor for detecting forces acting on the workpiece holding device when grinding the workpiece. Furthermore, the present invention relates to a method for grinding brake discs.

Description

[Technical field]

[0001] The present invention relates to a double-sided grinding machine including a first machine part having a first grinding disc and a second machine part having a second grinding disc, the spacing between the first grinding disc and the second grinding disc being adjustable along a machine axis, and further including a workpiece holding device for holding a workpiece. Summary of the Invention [Problem to be solved by the invention]

[0002] SUMMARY OF THE DISCLOSURE The object of the present invention is to provide a double-sided grinding machine which is particularly well suited for grinding workpieces which have a very hard surface but which have a relatively low form stability. [Means for solving the problem]

[0003] This problem is solved in a double-sided grinding machine of the type mentioned at the beginning in that the workpiece holding device comprises at least one force sensor for detecting the force acting on the workpiece holding device when grinding the workpiece.

[0004] The detection of the forces acting on the workpiece holding device allows the forces acting on the workpiece itself to be estimated. Knowledge of these forces makes it possible to control the grinding process of the workpiece or the processing parameters of the double-sided grinding machine in dependence on the detected forces.

[0005] In particular, the detection of forces detected at the workpiece holding device is a prerequisite for making it possible to equalize the forces acting on the workpiece from both sides of the double-sided grinding machine during the grinding process of the workpiece.

[0006] The at least one force sensor is preferably linked to a control device of the double sided grinding machine, which allows a direct feedback of the force sensor signal for its consideration in the control device.

[0007] In particular, the first machine part has a first feed drive for moving the first grinding disk along the machine axis and the second machine part has a second feed drive for moving the second grinding disk along the machine axis, which feed drives are preferably controllable by the control device in such a way that the machining forces acting on the workpiece by the first and second grinding disks can be balanced with each other depending on the signal of at least one force sensor, whereby the force acting on the workholding device can be used as an input quantity for the operation of the feed drive to equalize the machining forces acting on the workpiece by both grinding disks.

[0008] The workpiece holding device preferably comprises a workpiece holder for connection with the workpiece to be ground, which may be constituted by an adapter having a mechanical interface with the workpiece with a specific interface geometry.

[0009] The workpiece holder is preferably configured as a brake disc holder. When viewed along its central rotation axis (i.e. axially), brake discs for motor vehicles have a relatively low stability, especially in the region of the radially inner transition between the annular brake disc area and the central brake disc hub. High demands are imposed on the grinding of the surface of the annular brake disc area, especially if the surface of such an area has a very hard wear protection layer. This applies in particular to brake discs, which should be low-wear in order to avoid fine dust. For this purpose, a coating is used that has a support material for embedding hard carbide particles. The support material is, for example, a stainless steel alloy for corrosion protection reasons, which is relatively soft and flexible, making it difficult to apply high processing forces to the carbide particles, at least insofar as this may entail a deformation of the annular brake disc area relative to the brake disc hub.

[0010] That is, in the above-described grinding process of the brake disc, the working surface of the grinding disc must be pressed with high force against the respective brake disc layer on the surface of the brake disc area in order to enable grinding of the hard carbide particles. However, since the brake disc is flexible in a direction parallel to the central axis of the brake disc as described above, it may happen that the brake disc is deformed axially between the first grinding disc and the second grinding disc, i.e. parallel to the machine axis, during the grinding process, so that grinding of both brake pad layers is carried out while the brake disc is in a deformed state. In this way, it is possible to grind the brake pad coating with a satisfactory quality. However, if the brake disc is deformed back again after the end of the grinding process, it will have an inaccurate rotational runout.

[0011] The double-sided grinding machine according to the invention makes it possible to detect the above-mentioned deforming forces and to influence the processing parameters of the double-sided grinding machine so that these forces are minimized. In this way, despite the application of a brake disc coating, the brake disc can be ground with high grinding forces, so that the ground brake disc coating adheres to the maximum roughness values ​​and the brake disc has a high degree of precision after the grinding process is completed.

[0012] The workholding device preferably has a spindle drive for rotating the work holder, which may be arranged coaxially with respect to the axis of rotation of the workpiece or may be offset therefrom.

[0013] Furthermore, the workpiece holding device preferably has a holding structure for supporting the workpiece holder, which is particularly well suited for arranging the at least one force sensor, since the holding structure is stationary or at least does not move about the rotation axis when the workpiece is ground.

[0014] Furthermore, the double-sided grinding machine preferably also includes a feed drive, by means of which the holding structure can be moved transversely, in particular perpendicularly, to the machine axis. This simplifies the positioning of the workpiece in the working space formed between the respective grinding disks of the double-sided grinding machine. The feed can take place, for example, radially with respect to the rotation axis of the grinding disks, or along a pivot path about a pivot axis that runs parallel to the machine axis and spatially offset.

[0015] At least one force sensor can be configured, for example, as a strain gauge. This makes it possible to detect the stress acting on an area of ​​the workpiece holding device due to tensile and / or compressive loads. It is particularly preferred that the force sensor is arranged on the holding structure. This is particularly preferred if the holding structure is configured with such a high stiffness that the forces exerted by the grinding disk on the workpiece and from the workpiece on the workpiece holding device only cause negligible deformations of the holding structure, but nevertheless it is possible to detect the forces caused by the grinding process of the workpiece by measuring the stresses inside or on the surface of the holding structure.

[0016] Force sensors configured as strain gauges allow for indirect detection of the machining forces. Additionally or alternatively, direct measurement of the forces acting on the workpiece holding device is also possible.

[0017] For this purpose, the workpiece holding device preferably includes a linear guide, the linear guide axis of which runs parallel to the machine axis, the linear guide having two guide members, the first guide member being connected to the holding structure and the second guide member being connected to the frame, and at least one force sensor being connected to the first and second guide members for detecting the forces acting between the respective guide members. The holding structure is then subjected to a resultant force, the value and direction of which are determined by the difference between the machining force of the first grinding disk and the machining force of the second grinding disk. This resultant force is transmitted from the workpiece via the workpiece holder to the holding structure and from there to one of the guide members. From there, this force is transmitted via the second guide member to a force sensor supported on the frame.

[0018] A preferred guide member includes at least one rail and at least one carriage guided along the rail.

[0019] Furthermore, the sensor axis of the at least one force sensor preferably runs parallel to the machine axis, which allows a particularly simple detection of machining forces caused by the grinding disk which act parallel to the machine axis.

[0020] One particularly preferred force sensor is a piezoelectric force sensor, which can detect very high forces with minimal deformation and convert them into electrical signals with high resolution.

[0021] The force sensor may be a compressive force sensor, or a prestressed compressive force sensor, or a sensor for detecting compressive and tensile forces. For economic reasons, it is preferred to use a compressive force sensor or a prestressed compressive force sensor.

[0022] The selection of the appropriate sensor also depends on the orientation of the machine axes of the double-sided grinding machine. If the double-sided grinding machine has a machine axis oriented vertically, at least one part of the workpiece holding device will load with its weight on the force sensor, which can be additionally loaded (higher pressure) or deloaded (lower pressure) depending on the processing forces by the first and second grinding disks. If the self-weight of the workpiece holding device is not sufficient, it is also possible to use a compression force sensor that is prestressed and calibrated at the factory, or that is prestressed only when mounted on the double-sided grinding machine (for example with the aid of an expansion bolt) and subsequently calibrated. The prestressing of the compression force sensor makes it possible to detect not only compressive forces but also tensile forces.

[0023] In the case where the machine axis of the double-sided grinding machine is oriented horizontally, in particular prestressed compressive force sensors or sensors for detecting compressive and tensile forces can be used. For horizontally oriented machine axes, the feed drive of the grinding disk can be designed with relatively low power, since the associated machine parts and the rotary drive integrated therein for driving the grinding disk in rotation do not have to be lifted against the force of gravity along the machine axis.

[0024] The invention further relates to a method for grinding brake discs, in particular automotive brake discs, using the above-described double-sided grinding machine, which method comprises the steps of: a) positioning a partial area of ​​a brake disc in a working space arranged between a first grinding disc and a second grinding disc; b) performing a retraction stroke of the first abrasive disc by feeding the first abrasive disc in a direction towards the first brake disc surface facing the first abrasive disc through a retraction stroke path until contact is detected by the at least one force sensor and / or additional sensor; c) a forward stroke of the first abrasive disc is performed by feeding the second abrasive disc in a direction towards a second brake disc surface facing the second abrasive disc, the forward stroke of the first abrasive disc being performed by a backward stroke path, until contact is detected by the at least one force sensor and / or an additional sensor; d) both grinding discs are moved towards each other at the same cutting speed; e) adapting the infeed speed of at least one of the grinding disks as a function of the signal of the force sensor; Includes:

[0025] In the method according to the invention, the contact with both brake disc surfaces ensures that the initial peeling takes place simultaneously on both brake disc surfaces, thus avoiding that only one of the grinding discs comes into contact with the brake disc, which, due to the already described instabilities of the brake disc, can result in a strong deformation of it in the axial direction.

[0026] The detection of the contact between the grinding disc and the brake disc surface can be performed with the aid of at least one force sensor, which detects the contact force caused by such contact. Additionally or alternatively, the detection of the contact can be performed with the aid of an additional sensor, for example a structure-borne sound sensor.

[0027] The contact with the opposing brake disc surfaces makes it possible to define an initial reference position of the grinding disc. In order that the determination of the reference position is not influenced by the respective other grinding disc, a retraction stroke of the first grinding disc is performed after the first grinding disc has come into contact with the first brake disc surface by a certain retraction stroke. This allows the second grinding disc to come into contact with the opposite second brake disc surface - without being hindered by the first grinding disc - and thus to define the reference position of the second grinding disc. The first grinding disc is then again moved towards the first brake disc surface by the aforementioned retraction stroke, so that at the start of the grinding process of the brake disc, both grinding discs come into contact with both brake disc surfaces, respectively. On this basis, the infeed of both grinding discs is performed with the same infeed speed in the direction of approaching each other.

[0028] In the case where the surface quality of both brake disc surfaces is identical, at least one force sensor of the tool holder is not subjected to forces that require an adaptation of the cutting speed of the grinding disc. However, as soon as the geometry and / or quality of both brake disc surfaces differ from each other, it is assumed that one of the grinding discs exerts a higher machining force on its associated brake disc surface than the other grinding disc exerts on the other brake disc surface. Such a difference between the respective machining forces can be detected by at least one force sensor, which generates a signal that can be used to operate the grinding disc exerting a high machining force on the brake disc surface at a lower cutting speed. In this way, excessively high machining forces can be reduced.

[0029] The equal value of the infeed rate according to d) is the maximum feed rate, and the adaptation of the feed rate according to e) is preferably accompanied by a reduction in the infeed rate of one of the grinding discs, which means that in the ideal case the brake disc is machined from both sides with the maximum infeed rate, but if necessary the infeed rate of the grinding disc which is pressing with too high a machining force against the associated brake disc surface is reduced.

[0030] Further features and advantages of the invention are the subject of the following description and the drawings of exemplary embodiments. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 is a perspective view showing one embodiment of a double sided grinding machine. [Diagram 2] FIG. 2 is a perspective view showing a module of the double sided grinding machine of FIG. [Diagram 3] FIG. 3 is a perspective view showing another embodiment of a double sided grinding machine. [Figure 4] FIG. 4 is a side view showing the double-sided grinding machine of FIG. [Diagram 5] FIG. 5 is a perspective view showing another embodiment of a double sided grinding machine. [Figure 6a] FIG. 6a is a front view of the double sided grinding machine of FIG. [Figure 6b] FIG. 6b is a front view of the double sided grinding machine of FIG. [Figure 6c] FIG. 6c is a front view of the double sided grinding machine of FIG. [Figure 6d] FIG. 6d is a front view of the double sided grinding machine of FIG. [Figure 6e] FIG. 6e is a front view of the double sided grinding machine of FIG. [Figure 7a] FIG. 7a is a graph showing the force profile in the workholding device of the double sided grinding machine of FIG. 5 versus the infeed speed of the grinding disc. [Figure 7b] FIG. 7b is a graph showing the force profile in the workholding device of the double sided grinding machine of FIG. 5 versus the infeed speed of the grinding disc. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] An embodiment of a double-sided grinding machine is designated generally by the reference number 10 in the drawings. The machine 10 comprises a machine frame 12 with a vertical machine axis 14 along which a first machine part 16 with a first grinding disc 18 and a second machine part 20 with a second grinding disc 22 are movably arranged.

[0033] The first grinding disc 18 and the second grinding disc 22 can be designed as hub discs, i.e. each have an annular working surface.

[0034] Between the mutually facing working surfaces of the grinding discs 18 and 22 a working space 24 is formed, into which a workpiece 26, in particular in the form of a brake disc 28, can be locally inserted.

[0035] The workpiece 26 is held by a workpiece holder 30 which is movable along a horizontal feed axis 32 to move the workpiece 26 into and out of the workspace 24 .

[0036] The workpiece 26 is connected, for example by screwing, to a workpiece holder 34. The workpiece holder 34 can be rotated by a spindle drive 36 about a central axis 38 of the workpiece 26, so that the workpiece 26 connected to the workpiece holder 34 also rotates about the central axis 38. The central axis 38 runs parallel to the machine axis 14.

[0037] The workpiece holder 34 is supported in a holding structure 40 which is movable along the feed axis 32 by a feed drive (not shown as it is known per se).

[0038] The retaining structure 40 is shown from an underneath perspective as part of a module of the double sided grinding machine 10 shown in FIG.

[0039] The holding structure 40, in the embodiment shown, comprises a housing 42 of the spindle drive 36. The holding structure 40 has at least one wall section 44, which is subjected to extension or compression as a result of a force acting along the central axis 38. A force sensor 46 configured as a strain gauge is arranged in the wall section 44.

[0040] The embodiment of double-sided grinding machine 10 shown in Figures 3 and 4 has a structure comparable to the double-sided grinding machine 10 described above with reference to Figures 1 and 2. In the following, only the differences with respect to the double-sided grinding machine 10 of Figures 1 and 2 will be described.

[0041] The double-sided grinding machine 10 of Figures 3 and 4 includes a workpiece holding device 30 having a linear guide 48 defining a linear guide axis 50 extending with the machine axis 14. The linear guide 48 includes two guide members 52 and 54 that are mutually guided along the linear guide axis 50. The first guide member 52 is attached to a holding structure 40 which also includes the housing 42 of the spindle drive 36. The second guide member 54 is attached to a frame 56 that is immobile perpendicular to the feed axis 32 and parallel to the machine axis 14.

[0042] This double-sided grinding machine 10 includes a force sensor 46, in particular in the form of a piezoelectric force sensor, which is coupled along a sensor axis (not numbered, running parallel to the linear guide axis 50) to the holding structure 40 on the one hand and to the frame 56 on the other hand. By way of example, this force sensor 46 is a compressive force sensor or a prestressed compressive force sensor.

[0043] Thus, in principle, the holding structure 40 is supported on the frame 56 so as to be movable along the linear guide axis 50. However, since the relatively stiff force sensor 46 is connected both to the holding structure 40 and to the frame 56, the actual path of movement of the holding structure 40 along the linear guide axis 50 relative to the frame 56 can be ignored. This is intended because the force sensor 46 should detect the forces introduced by the grinding process by the first and second grinding discs 22 into the workpiece 26, in particular in the form of the brake disc 28, with minimal deformation.

[0044] The double-sided grinding machine 10 shown in Figure 5 has a structure comparable to that of the double-sided grinding machine 10 of Figures 3 and 4, but in contrast has a horizontal machine axis 14. The double-sided grinding machine 10 of Figure 5 also has a linear guide 48 with a linear guide axis 50 that also runs parallel to the machine axis 14 and is horizontal.

[0045] The linear guide device 48 includes guide members 52, 54 configured as a guide rail and as a carriage guided along the rail, respectively. Such guide members are also provided in the case of the linear guide 48 of the double-sided grinding machine 10 of FIGS.

[0046] The force sensor 46 of the double sided grinder 10 of Figure 5 is also a piezoelectric sensor. Illustratively, the force sensor 46 may be a prestressed compressive force sensor, or a sensor configured to detect compressive and tensile forces.

[0047] A method of grinding a workpiece 26 in the form of a brake disc 28 will now be described with reference to the double-sided grinding machine of FIG.

[0048] 6a to 6e only show the workholding device 30 including the brake disc 28 and the grinding discs 18 and 22, respectively. The grinding discs have respective working surfaces 56 and 58 which cooperate with corresponding brake disc surfaces 60 to 62, respectively, of the brake disc.

[0049] In an initial state (see FIG. 6 a ), the working faces 56 and 58 of both grinding discs 18 and 22 are spaced apart from both brake disc surfaces 60 and 62 .

[0050] The brake disc 28 is inserted into the working space 24 (see FIG. 6a). On this basis, the first grinding disc 18 is fed by the first feed drive of the first machine part 16 along the machine axis 14 in the direction towards the brake disc 28 (see FIG. 6b) until the working surface 56 of the first grinding disc 18 comes into contact with the first brake disc surface 60 of the brake disc 28. During this contact, the brake disc 28 is driven in rotation by the spindle drive 36. The grinding disc 18 also rotates and is driven about the machine axis 14 by a rotation drive, which is known per se and is not shown.

[0051] Contact between the working surface 56 of the first grinding disc 18 and the first brake disc surface 60 causes a compressive force to be exerted against the first brake disc surface 60, which is transmitted via the tool holder 34 to the holding structure 40 of the workholding device 30 and from there acts on the force sensor 46. The force sensor 46 is on the other hand supported by the frame 56 and is thus subjected to a compressive force, which is shown as force 64 in Figures 7a and 7b.

[0052] Subsequently (see FIG. 6c), the first grinding disc 18 is moved backwards by a backward stroke 66 by the first feed drive of the first machine part 16, so that the first grinding disc 18 is again spaced apart from the brake disc 28. This leads in FIGS. 7a and 7b to an area 68 of the force curve and a corresponding relief of the force sensor 46.

[0053] Subsequently (see FIG. 6d), the second grinding disc 22 is moved along the machine axis 14 by the second feed drive of the second machine part 20 until the working surface 58 of the second grinding disc 22 comes into contact with the second brake disc surface 62 of the brake disc 28. During this contact, the brake disc 28 is driven in rotation by the spindle drive 36. The grinding disc 22 also rotates and is driven about the machine axis 14 by a rotation drive, which is known per se and is not shown. This contact leads to the holding structure 40 exerting a tensile force on the force sensor 46, which in FIGS. 7a and 7b corresponds to an area 70 of the force curve.

[0054] Subsequently, the first grinding disc 18 is again advanced by the retraction stroke 66 (see Figures 6d and 6e) until it again comes into contact with the brake disc 28. This state corresponds to the region 72 of the force curve in Figures 7a, 7b, in which the force sensor 46 is ideally subjected to neither tensile nor compressive forces.

[0055] Given the situation shown in Fig. 6e, the actual grinding process of the brake disc 28 is started, during which the grinding discs 18 and 22 move towards each other with equal infeed speeds in order to remove the surface coating of the brake disc surfaces 60 and 62, while deformation forces caused by different machining forces should be avoided. As long as the quality and geometry of the brake disc surfaces 60 and 62 are identical, equal infeed speeds of both grinding discs can be maintained and the force sensor 46 is not subjected to compressive or tensile forces. Such an ideal situation is shown in Fig. 7a, where infeed speed 74 corresponds to the infeed speed of the first grinding disc 18 and infeed speed 76 corresponds to the infeed speed of the second grinding disc 22.

[0056] Figure 7b shows a force profile that deviates from the ideal state, which leads to an adaptation of the feed rates 74 and 76. Given the state shown in Figure 6e and a force sensor 46 that is not subjected to compressive and tensile forces, it may occur, for example, during machining of the brake disc 28 that the working surface 56 of the first grinding disc 18 comes into contact with the surface coating of the first brake disc surface 60 over a larger contact area than the working surface 58 of the second grinding disc 22 comes into contact with the surface coating of the second brake disc surface 62. This leads to the first grinding disc 18 exerting a higher machining force on the brake disc 28 than the second grinding disc 22. This is detected by the force sensor 46, i.e. as a compressive force 78 that is different from zero (see Figure 7b).

[0057] If the infeed speeds 74 and 76 of both grinding discs 18 and 22 were maintained, the brake disc 28 would be deformed by the high pressure of the grinding disc 18 in a direction towards the second grinding disc 22 relative to the workpiece holder 34. To avoid this, the infeed speed of the first grinding disc 18 is reduced (see region 80 in FIG. 7b) until the force sensor 46 is again free of force.

[0058] This can be followed by machining with maximum cutting speeds 74 and 76. If, for example, the second grinding disc 22 acts on the brake disc 28 with a higher force compared to the first grinding disc 18, the force sensor 46 is subjected to a tensile force (see reference number 82 in FIG. 7b). In order to avoid deformation of the brake disc 28 in the direction towards the first grinding disc 18, the cutting speed of the second grinding disc 22 is reduced in this case (see the region designated by reference number 84 in FIG. 7b) until the force sensor 46 is again free of force.

[0059] As shown in FIG. 7b, the above-described change in cutting speed can be performed multiple times; for example, the cutting speed 74 of the first grinding disc 18 and / or the cutting speed 76 of the second grinding disc 22 can be reduced and increased again multiple times.

[0060] The reduction of the cutting speed 74 and / or 76 can also be performed down to "zero" if necessary, ie until the grinding discs 18 and / or 22 come to a halt along the machine axis 14.

Claims

1. A double-sided grinding machine (10) comprising a first machine part (16) having a first grinding disc (18) and a second machine part (20) having a second grinding disc (22), the spacing between the first grinding disc (18) and the second grinding disc (22) being adjustable along a machine axis (14), and further comprising a workpiece holding device (30) for holding a workpiece (26), characterized in that the workpiece holding device (30) comprises at least one force sensor (46) for detecting a force acting on the workpiece holding device (30) when grinding the workpiece (26).

2. 2. The double-sided grinding machine (10) according to claim 1, characterized in that at least one of the force sensors (46) is linked to a control device of the double-sided grinding machine (10).

3. 3. The double-sided grinding machine (10) according to claim 2, characterized in that the first machine part (16) has a first feed drive for moving the first grinding disc (18) along the machine axis (14) and the second machine part (20) has a second feed drive for moving the second grinding disc (22) along the machine axis (14), the feed drive being controllable by the control device so that, depending on the signal of at least one of the force sensors (46), the machining forces acting on the workpiece (26) by the first grinding disc (18) and the second grinding disc (22) can be balanced with each other.

4. 4. The double-sided grinding machine (10) according to claim 1, wherein the workpiece holding device (30) comprises a workpiece holder (34) for connection with the workpiece (26) to be ground.

5. 5. The double-sided grinding machine (10) according to claim 4, characterized in that the workpiece holder (34) is configured as a brake disc holder.

6. 6. A double-sided grinding machine according to claim 4 or 5, characterized in that the workpiece holding device (30) has a rotary drive (36) for rotating the workpiece holder (34).

7. The double-sided grinding machine (10) according to any one of claims 4 to 6, characterized in that the workpiece holding device (30) has a holding structure (40) for supporting the workpiece holder (34).

8. 8. The double-sided grinding machine (10) according to claim 7, characterized in that the double-sided grinding machine (10) comprises a feed drive by means of which the holding structure (40) can be moved transversely, in particular perpendicularly, to the machine axis (14).

9. The double-sided grinding machine (10) according to any one of the preceding claims, characterized in that at least one of the force sensors (46) is configured as a strain gauge.

10. A double-sided grinding machine (10) according to claim 9, which relies on claim 7 or 8, characterized in that the force sensor (46) is arranged on the holding structure (40).

11. The double-sided grinding machine (10) according to any one of claims 1 to 10, characterized in that the workpiece holding device (30) includes a linear guide (48), the linear guide axis (50) of which extends parallel to the machine axis (14), the linear guide (48) has two guide members (52, 54), the first guide member (52) being connected to the holding structure (40) and the second guide member (54) being connected to a frame (56), and at least one force sensor (46) being connected to the holding structure (40) and the frame (56) for detecting a force acting between the holding structure (40) and the frame (56).

12. 12. The double-sided grinding machine (10) according to claim 11, characterized in that the guide members (52, 54) include at least one rail and at least one carriage guided along the rail.

13. 13. Double-sided grinding machine (10) according to any one of claims 1 to 12, characterized in that the sensor axis of at least one said force sensor (46) extends parallel to said machine axis (14).

14. The double-sided grinding machine (10) according to any one of the preceding claims, characterized in that at least one of the force sensors (46) is a piezoelectric force sensor.

15. 15. The double-sided grinding machine (10) according to claim 1, characterized in that at least one of the force sensors (46) is a compressive force sensor, or a prestressed compressive force sensor, or a sensor for detecting compressive and tensile forces.

16. A method for grinding brake discs (28), in particular automotive brake discs, using a double-sided grinding machine (10) according to any one of claims 1 to 15, comprising: a) positioning a partial area of ​​the brake disc (28) in a working space (24) disposed between the first grinding disc (18) and the second grinding disc (22); b) performing a retraction stroke of the first grinding disc (18) along a retraction stroke path (66) by feeding the first grinding disc (18) in a direction towards a first brake disc surface (60) facing the first grinding disc (18) until contact is detected by at least one of the force sensors (46) and / or an additional sensor; c) performing a forward stroke of the first grinding disc (18) along the reverse stroke path (66) by feeding the second grinding disc (22) in a direction towards a second brake disc surface (62) facing the second grinding disc (22) until contact is detected by at least one of the force sensors (46) and / or an additional sensor; d) the first grinding disc (18) and the second grinding disc (22) are both cut in a direction toward each other with the same cutting speed; e) adapting the infeed speed of at least one of the first grinding disc (18) and the second grinding disc (22) depending on the signal of the force sensor (46); and A method comprising:

17. 17. The method according to claim 16, characterized in that the infeed speeds with equal values ​​according to d) are maximum infeed speeds, and the adaptation of the infeed speeds according to e) involves a reduction in the infeed speed of one of the first grinding disc (18) and the second grinding disc (22).

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