Grinding machine and grinding method for grinding coated brake discs

Abstract

A grinding machine (100) for grinding substantially plane-parallel annular workpiece surfaces on disk-shaped workpiece sections (BA) of workpieces (WS1, WS2) comprises a grinding unit (121) such as a dual-disk grinding unit having two tool spindles (132-1, 132-2) arranged coaxially with one another and each supporting a grinding disk (130-1, 130-2), the grinding disks arranged with abrasive sides (135-1, 135-2) facing one another and defining a grinding space (133), and at least one workpiece spindle (154) having a workpiece holder (155) for holding the workpiece (WS1, WS2) in a rotationally fixed manner so that the workpiece section (BA) of the held workpiece extends in an arc through the grinding space for grinding. The grinding machine comprises a first position data determination system for determining workpiece position data representing an axial position of a workpiece surface (O1, O2) at at least one surface location relative to a reference coordinate system (RKS) fixed to the machine, and a second position data determination system for determining tool position data representing an axial position of a grinding side surface (135-1, 135-2) facing the workpiece surface (O1, O2) relative to the same reference coordinate system (RKS). A control unit (190) of the grinding machine is configured to control at least one grinding parameter in at least one stage of the grinding operation in response to the workpiece position data and / or the tool position data in at least one operating mode. The grinding machine can be used to grind the workpiece surface of an annular brake section of a brake disc.

Description

[Technical Field]

[0001] The present invention relates to a grinding machine and a grinding method for grinding substantially planar annular workpiece surfaces on a disc-shaped workpiece portion of a workpiece. The preferred field of application is the grinding of the surfaces of brake discs, in particular the annular braking parts of coated brake discs. [Background technology]

[0002] A brake disc is a part of a disc brake that is connected to a wheel for rotation with it and on which brake pads fixed to a caliper act to slow down the rotational motion. The brake disc is approximately point-symmetric or rotationally symmetric with respect to an axis through which the axis of rotation of the brake disc passes. The brake disc has a central hub portion and a circular braking portion surrounding the hub portion, with the braking portion having two axially opposing free surfaces that function as the friction surfaces of the brake disc.

[0003] Conventional mass-produced brake discs are typically made from gray cast iron, which currently reaches its limits, particularly in terms of corrosion and wear behavior. Brake discs made from ceramic materials are also available, but these are expensive and have only been used in premium vehicles.

[0004] Pending tightening regulations on automotive particulate emissions are expected to mean that future automotive brake discs will need to be designed to release fewer particles during braking. One approach in this regard is to coat the brake disc, or its surface portion that serves as the friction surface, with a thin functional layer made of a more wear-resistant material. In a coated brake disc, the surface of the annular braking portion each carries a functional layer that is rotationally symmetrical about the axis of rotation, and whose free surface is in the form of the friction surface of the brake disc.

[0005] The manufacturing process for coated brake discs involves one or more coating operations to coat the surface of the braking portion of the brake disc with a functional layer that can have a wear-reducing function thanks to its relatively high mechanical hardness. Alternatively or additionally, it can also have a corrosion-inhibiting effect. Such functional layers often consist essentially of metal and can have a single layer or multiple layers with different properties. Such coatings can be applied, for example, by flame spraying or laser cladding. Typical layer thicknesses can be in the range of 50 μm and 350 μm, for example. Generally, the coating is applied on both sides. Documents EP2 746 613 A2 and WO2019 / 021161 A1 disclose examples of coated brake discs.

[0006] Depending on the coating process and coating material, the free surface of the finished coating can have different properties: functional layers are generally relatively mechanically hard and have a relatively rough surface after coating.

[0007] The downstream grinding process is intended to produce a sufficiently flat surface on the coating that is optimized for braking performance. In this case, the requirements for the friction surface of the brake disc can be, for example, an average roughness Ra determined in accordance with DIN EN ISO 4288 in the range of 1 μm to 3 μm-3.2 μm, with a flatness deviation of at most 20 μm (see WO 2021 / 224308 A).

[0008] EP 3 789 512 A1 discloses a system for coating and subsequent grinding of brake discs. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] European Patent No. 2 746 613 A2 [Patent Document 2] International Publication No. 2019 / 021161A1 [Patent Document 3] European Patent No. 3 789 512 A1 Summary of the Invention [Problem to be solved by the invention]

[0010] Against this background, the present invention addresses the problem of providing a grinding machine and a grinding method that can be used in the production of workpieces, for example in the form of brake discs, in particular coated brake discs, and that allow systematically producing ground workpieces within tight manufacturing tolerances even in the case of small batch sizes, and in the process allow a suitable optimization of the grinding process, for example with regard to costs and / or processing times. [Means for solving the problem]

[0011] To solve this problem, the present invention provides a grinding machine having the features of claim 1. Furthermore, a grinding method is provided having the features of claim 14. Preferred developments are defined in the dependent claims. The language of all claims forms part of the content of this description by reference.

[0012] According to one aspect of the present invention, there is provided a grinding machine for grinding substantially plane-parallel annular workpiece surfaces on a disc-shaped workpiece portion. In a preferred field of application, the workpiece is a brake disc, the annular braking portion of which is intended to be ground on both sides.

[0013] Due to the structural particularities and the design of the motion control system having a control unit and its communicating hardware components (including sensors and includers) and software components (including control and evaluation software), the grinding machine is configured or can be configured by providing corresponding operating modes to perform specific grinding processes that could not be performed with conventional grinding machines.

[0014] The grinding machine is configured in a manner similar to a double-sided surface grinding machine. The grinding machine includes a grinding unit having two tool spindles, which are arranged or can be arranged coaxially with each other on a machine frame, each holding a grinding wheel. The grinding wheels are arranged with opposing abrasive sides that define a grinding space of axial height that is axially variable. Each of the grinding wheels can be rotated independently of the other grinding wheels by an associated rotary drive with a definable speed profile about an associated rotation axis, and can be fed axially by a feed drive with a feed parameter, e.g., a definable feed rate, that can be determined by linear displacement parallel to the associated rotation axis. Optionally, the grinding wheels can also be fed perpendicular to the rotation axis, i.e., radially relative to the rotation axis.

[0015] According to the present application, in a "coaxial" arrangement of tool spindles, the rotation axes coincide within manufacturing tolerances. Slight deviations from mathematically strict coaxiality due to parallel offset or tilting of one or both tool spindles may occur, for example, under one-sided loading during grinding.

[0016] The grinding machine further comprises at least one workpiece spindle having a workpiece receiver for receiving a co-rotating workpiece, the workpiece receiver being rotatable by a rotary drive about an axis of rotation extending substantially parallel to the axis of rotation of the grinding wheel. During at least one stage of the grinding operation, the workpiece spindle is arranged in a working position so that the workpiece portion of the receiver extends in an arc through the grinding space. Depending on the design of the grinding machine, the workpiece spindle may be fixed in the working position or may be movable. For example, the workpiece spindle may be moved to the working position to perform the grinding operation and then returned from the working position after the grinding operation is completed. The rotating workpiece spindle may be stationary during the material removal phase while the grinding wheel is being fed. In this way, a variation of transverse double-sided grinding can be realized, in which the feeding operation extends transversely, in particular perpendicular to the workpiece surface being processed.

[0017] Alternatively or additionally, in some cases, during one stage of the grinding operation, the workpiece spindle and the grinding unit can be moved relative to one another, for example, by driving the workpiece spindle to move perpendicularly to its axis of rotation while the grinding wheel is in contact with the workpiece surface. In this way, a variation of the longitudinal flank double grinding process is realized, in which the feed movement is carried out along the workpiece surface, i.e., parallel to it, for example, in a direction extending radially to the axis of rotation of the tool and / or workpiece.

[0018] The grinding process can have both variations, for example, whereby on the upstream side rough cutting is performed by double longitudinal grinding, whereby the main surface of removal is achieved with a high removal rate, and then on the downstream side finishing is performed by double transverse grinding, whereby the final dimensions and the desired surface quality are achieved with a low removal rate.

[0019] The grinding machine also has an operating control system with a control unit for controlling the operation of the grinding machine, which controls the connected actuators, in particular the workpiece movement drive and the tool movement drive, via appropriate control signals. The control device also receives sensor signals from the connected sensors and processes these, in particular for the purpose of targeted control of the actuators in the control circuit.

[0020] The term "axial direction" in this application refers to the direction in which the rotation axis extends toward the workpiece and toward the tool. The axial direction can be set, for example, vertical (parallel to the direction of gravity), horizontal, or at an angle to the horizontal and vertical. The grinding wheel is fed in the axial direction.

[0021] That the grinding machine is suitable for performing a particular grinding process is evident from the fact that the grinding machine has a first position data determination system for determining workpiece position data and a second position data determination system for determining tool position data, and that the control unit is configured, in at least one operating mode, to control at least one grinding parameter of the grinding process in at least one stage of the grinding process depending on the workpiece position data and / or the tool position data.

[0022] Workpiece position data is data that represents the axial position of the workpiece surface being ground at least one surface location relative to a machine-based reference coordinate system, while tool position data is data that represents the axial position of the side surface of the abrasive that faces the workpiece surface relative to the same reference coordinate system.

[0023] The term "axial position" in this case refers to the position or surface position of the corresponding surface in the axial direction extending parallel to the axis of rotation of the grinding wheel and the axis of rotation of the workpiece.

[0024] Such a grinding machine thus has two devices that can be operated independently of each other, and both the axial workpiece position and the axial tool position can be determined, in particular relative to the same reference coordinate system. In this way, corresponding position data can be directly offset from each other during data evaluation in order to determine the spatial relationship in the axial direction between the abrasive flank and the respectively associated workpiece surface.

[0025] This possibility of offsetting workpiece-related and tool-related axial position data in the same reference coordinate system offers many advantages, which will now be explained by way of example.

[0026] The present invention takes into account, inter alia, the knowledge that a grinding process or operation should always be adapted to specific input conditions and user requirements, which may vary. Thus, the input dimensions of a workpiece (before grinding begins) may vary from workpiece to workpiece, even if the workpieces are nominally identical (in terms of specifications) and the previous processing (e.g., coating) was performed in a manner that nominally does not change from workpiece to workpiece. Changing from one workpiece to the next generally requires a change in the grinding process. Furthermore, the abrasives used may not always have the same characteristics, which may affect the grinding process. Finally, user requirements may differ. Particularly when grinding mechanically very hard brake discs or coated brake discs that are initially very rough, there is a sensitive interaction between tool wear during grinding and material removal efficiency. Therefore, it would be desirable to always be able to set the optimal working point from the user's perspective. The present invention creates the prerequisites for this.

[0027] According to one development, the control unit is configured, in at least one operating mode, to control, depending on the workpiece position data and / or the tool position data, (i) the feed rate of one or both grinding wheels, (ii) the speed of one or both grinding wheels, and / or (iii) the speed and / or direction of rotation of the workpiece spindle that carries the workpiece for the grinding operation. Each of these grinding parameters can affect in a targeted manner the material removal rate and / or the wear of the tool occurring during grinding and / or the quality of the grinding result. Often, two or more grinding parameters are simultaneously changed by the control actions.

[0028] During at least one stage of the grinding operation, the workpiece spindle carrying the workpiece is placed in a working position characterized by the workpiece portion to be machined extending in an arc through the grinding space. To perform the grinding operation, the workpiece and the grinding wheel are set to rotate about their rotation axes. During one stage of the grinding operation, the axial feed of the grinding wheel causes the abrasive surface to engage the relevant surface.

[0029] According to the present application, the term "grinding operation" includes in particular the phase in which material removal is performed, i.e., the phase in which at least one tool is in material-removing engagement with the workpiece. Furthermore, the grinding operation also includes phases in which the tool and the workpiece are not in contact, in particular the approach phase prior to material removal.

[0030] The workpiece position data and / or tool position data may be determined in a variety of ways.

[0031] Preferably, suitable measurements are carried out. According to a corresponding development, the first position data determination system is in the form of a first position measuring system for metrologically determining workpiece position data, and the second position data determination system is in the form of a second position measuring system for metrologically determining tool position data in the same reference coordinate system. A grinding machine configured for such measurements therefore has a first position measuring system for metrologically determining or measuring workpiece position data and a second position measuring system for metrologically determining or measuring tool position data. The position measuring systems are configured to determine, with sufficiently high accuracy, the axial position of the surface to be measured (the workpiece surface to be ground in the case of the first position measuring system, or the side surface of the abrasive in the case of the second position measuring system) relative to the reference coordinate system.

[0032] In principle, it would be possible to measure the workpiece externally before it is installed, i.e., outside the grinding machine, before it is received in the workpiece receiving section of the grinding machine. After installation, the relationship to the machine-internal reference coordinate system can be established.

[0033] However, according to one development, the workpiece is measured after it has already been installed, i.e., after it has been fixed in the workpiece receptacle of the workpiece spindle of the grinding machine. The first and second position measuring systems can thus be configured to measure the workpiece while it is attached to the workpiece receptacle. In-machine measurement of the workpiece avoids many sources of error. For example, it is not possible to exclude the possibility that the position of the workpiece may change after it has been inserted and held. Furthermore, geometric deviations, such as warpage, must also be taken into account.

[0034] In particular, the first and second position measuring systems can be configured to perform position measurements when the workpiece receiver with the workpiece is in the working position. This can be achieved in particular by a suitable arrangement of sensors for position measurement. This eliminates a source of error that may arise during measurements of the workpiece that are performed at a location away from the working position while the workpiece is being transferred to the working position.

[0035] In a preferred exemplary embodiment, the grinding machine is characterized in that it is configured to simultaneously measure workpiece position data and tool position data during at least one stage of the grinding operation, allowing real-time monitoring and, optionally, real-time adjustment of the sequence of grinding operations in a grinding process that simultaneously senses workpiece position data and tool position data of a grinding wheel provided for grinding the workpiece.

[0036] According to one development, the measurement of the surface position is carried out contactlessly, for which at least one contactless (non-tactile) sensor can be used, so that mechanical damage to the sensor system and optionally to the workpiece surface can be avoided if the measurement is carried out on a rotating workpiece and / or on a rotating grinding wheel.

[0037] Preferably, for the metrological determination of workpiece position data and / or tool position data, a distance measurement is carried out between at least one distance sensor of the associated position measuring system and the surface to be measured, the axial position of the distance sensor in the reference coordinate system being known with a correspondingly high degree of accuracy.

[0038] According to one development, the distance sensors can be calibrated at any time with a reference normal. For this purpose, the grinding machine has an internal calibration system with a reference element. The distance sensors are movable in a controlled manner within their respective working areas. Each distance sensor is assigned a reference element that is located within the working area of ​​the distance sensor and accessible for reference measurements. A reference element can be assigned to multiple distance sensors. The distance sensors are calibrated periodically or as needed and adjusted as necessary to ensure high measurement accuracy. In this way, traceable measurements can be generated. Traceability is known as the property of being able to or relating measurement results to a standard.

[0039] Preferably, a pneumatic measurement system with at least one measuring nozzle acting as a distance sensor is used for distance measurement. Such measurement systems, operating according to the nozzle / baffle principle, are also called pneumatic measurement systems. In this case, compressed air flows out of the measuring nozzle toward the surface being measured, and the characteristics of the compressed air, which depend on the distance between the measuring nozzle and the surface being measured, are measured and evaluated to determine the distance. Some systems measure back pressure, while others measure volumetric flow. In this application, pneumatic measurement systems have the advantage of being able to handle relatively rough machined surfaces with a relatively high measurement accuracy in the range of a few micrometers. Measurements performed during "wet" grinding operations have the advantage that the compressed air can be used to locally clear the measurement point, allowing distance measurements to capture the distance from the surface being measured even when the surface is covered with a liquid layer.

[0040] Alternatively, other distance measuring systems can be used, for example optical measuring systems, for example laser measuring systems, or measuring systems in which the sensor operates with radar radiation, or measuring systems with capacitive or inductive sensors.

[0041] According to one development, one distance sensor, preferably each distance sensor, is assigned an axial actuator for controllably changing the axial position of the distance sensor. For example, a measuring nozzle of a pneumatic measuring system can be mechanically coupled to a probe element of the tactile sensor, allowing for fine adjustment of the axial position of the measuring nozzle. If a tactile sensor is used to adjust the axial position of the measuring nozzle, the tactile sensor can simultaneously function as an axial position encoder, the encoder signal of which can be used to precisely determine the axial position of the associated distance sensor.

[0042] Some examples of available operating modes are described in the following text.

[0043] According to one development, the input inspection of the workpiece to be ground is provided by measuring the workpiece in the grinding machine. For this purpose, it is provided that, after the workpiece is fixed in the workpiece receiving part and before the start of the grinding operation, workpiece position data on the workpiece are determined for each surface of the end of the workpiece to be ground. Since the measurement is performed after the workpiece is fixed in the workpiece receiving part, the relationship between the determined position data and a machine-based reference coordinate system can be easily established.

[0044] During this measurement, it is preferable to provide that workpiece position data is determined for a plurality of circumferentially offset and / or radially offset surface locations. In this way, spatially resolved determination of axial positions, in particular two-dimensional spatially resolved measurements, is performed. As a result, workpiece shape data important for further processing can be determined, such as the thickness of the workpiece portion between substantially parallel workpiece surfaces, the curvature of the workpiece portion, often referred to as camber in the case of brake discs, and the circumferential and / or radial waviness. Therefore, the subsequent grinding process can be individually optimized, i.e., for each workpiece, by setting appropriate grinding parameters. The measured surface locations or measurement points can be arranged, for example, on concentric circles around the workpiece's axis of symmetry or on a spiral path around this axis.

[0045] In a corresponding manner, output testing of the ground workpiece can be performed within the grinding machine before said workpiece is removed from the workpiece receiver.

[0046] According to one development, a non-contact work approach control is realized in which, when feeding in the direction of the workpiece surface to be ground, the abrasive side of the grinding wheel is fed to a start position of the next feed stage, which is located at a safe distance in front of the workpiece surface to be processed, and in order to determine the start position, the initial workpiece position data and the initial tool position data are offset from each other before the start of material removal.As a result, an important contribution can be made to efficient process control during grinding, with as little lost time as possible, while simultaneously protecting the grinding tool and the workpiece.

[0047] This non-contact work approach control takes advantage of the fact that workpiece position data and tool position data exist in the same control system and can therefore be directly offset from one another, making it possible to determine the specific axial position at which the grinding wheel is initially fed, even before the grinding wheel's forward movement begins. In this case, the dimension of the safety distance ensures that, at the end of this first feed motion, no contact between the abrasive side and the workpiece surface is yet possible. Conveniently, in many embodiments, the safety distance is within the range of about 10 μm to about 100 μm. Preferably, in this case, the grinding wheel is fed at a first feed rate until it reaches a starting position, at which point the feed rate is automatically reduced to a lower, second feed rate. Thus, even for a relatively large advance distance, the first feed can be performed quickly for a relatively short period of time before the second feed phase begins in close proximity to the workpiece surface, at a much lower feed rate. This optionally continues until the grinding wheel and tool come into contact.

[0048] The second feed motion can be maintained at least until a nominal contact position is reached, which is the axial position at which the current tool position (i.e., the axial position of the abrasive grinding surface) corresponds to the initial workpiece position (i.e., the axial position of the workpiece surface being ground). As a result, the feed rate and / or other grinding parameters can be changed again at the onset of contact between the grinding wheel and the workpiece surface or just before or just after the initial contact to achieve an optimized material removal grinding process. The second feed motion can also be continued continuously beyond the initial contact time without changing the feed rate.

[0049] In some embodiments, particularly good adaptation of the grinding parameters of the grinding process to the state of the workpiece can be achieved in that tool position data is determined continuously or intermittently in a time-dependent manner, i.e., time-resolved, during the grinding operation, and the resulting time-dependent tool position data is processed to control the feed of the grinding wheel and / or at least one other grinding parameter. From the real-time observation of the axial position of the grinding surface, it is possible to draw conclusions, in particular regarding the grinding behavior of the workpiece and the tool.

[0050] Alternatively or additionally, it may be provided that during the grinding operation, workpiece position data is determined continuously or intermittently as a function of time, and the resulting time-dependent workpiece position data is processed to control the feed of the grinding wheel and / or at least one other grinding parameter.

[0051] In some embodiments, the control unit of the grinding machine is configured to, in one operating mode, correlate time-dependent tool position data determined during the grinding operation with time-dependent feed position data. The time-dependent feed position data can be determined from a control program for the grinding process and / or can optionally be measured with at least one position encoder. The above-described operating mode is also referred to in some embodiments as a grinding ratio optimization mode, since it creates an information basis for the grinding ratio at which the grinding process operates when observed. In particular, comparisons can be made of feed rates and the removal rates achievable thereby. These time-dependent comparisons can be used to determine wear and optimize wear accordingly.

[0052] The control unit can be configured to determine information about the current grinding ratio G and provide it for use, for example in the form of a G value or corresponding data. The grinding ratio is characteristic for each grinding process. The grinding ratio G, as defined herein, is expressed in volume units (e.g., cm 3 / cm 3) represents the ratio of material removal to wheel wear. If the aim at a certain stage of the grinding process is to achieve the highest possible dimensional and geometrical accuracy, the advance conditions can be set so that the amount of wheel wear is as small as possible. In contrast to this, if a high material removal rate is desired, for example to remove a significant thickness of material in a relatively short time, the feed rate can be set relatively high. Thus, with the possibility to determine workpiece position data and tool position data, the user has an important aid to optimize "his" grinding process.

[0053] In some embodiments, the operational unit may be used to input the desired target grinding ratio for the grinding process or the desired parameters required to determine the target grinding ratio. The control unit may be configured to calculate the current grinding ratio or current value permanently or at short time intervals based on data provided by the sensor system and compare it with the target grinding ratio. As long as the current G-value is within a tolerance range centered on the target grinding ratio, the grinding process will proceed satisfactorily. The control may monitor the maintenance of the G-value and control operation according to the comparison result. As an example, an alarm signal, e.g., acoustic, optical, and / or tactile, may be generated if the current G-value falls outside the tolerance range or is approaching the tolerance limit at a certain rate of change, indicating imminent breach. The operator can then take action and attempt to identify and possibly eliminate the cause of the undesired process change. The control unit may also be designed so that the process is automatically controlled to maintain the G-value. In this case, the machine control automatically ensures that the process more or less maintains the desired target grinding ratio within certain limits, without operator intervention.

[0054] A grinding machine can also have only one workpiece spindle positioned at the working position. The workpiece receiver can be loaded and unloaded, for example, by a robot or other handling device, or manually. However, often, the grinding machine is in the form of a multi-station grinding machine having a spindle carrier unit movable relative to the machine base, carrying at least one workpiece spindle mounted rotatably about its axis of rotation relative to the spindle carrier unit, and a transport system with a workpiece receiver. The grinding machine has at least two processing stations accessible by the workpiece spindle, including a loading station and at least one grinding station with at least one grinding unit. Thus, spatial separation of loading and unloading, on the one hand, and grinding, on the other, is possible, and these steps can be performed so as to overlap in time. As a result, production speed can be significantly increased. In some variations, the spindle carrier unit is rotatable and can be configured as a conventional turntable component. Alternatively, at least one spindle carrier unit can be provided that is translatable, for example, so that it can move linearly back and forth between the loading station and the work station on the grinding unit. If necessary, two linear systems can be provided that are mutually orthogonal and can be used interchangeably, for example to provide two loading stations.

[0055] Further advantages and aspects of the invention can be found in the claims and in the description of exemplary embodiments of the invention, which are explained in the following text with reference to the figures. [Brief explanation of the drawings]

[0056] [Figure 1] 1 is a schematic side view of an exemplary embodiment of a grinding machine configured to grind coated brake discs on both sides; FIG. [Figure 2] 1 is a workpiece side portion of a schematic diagram showing a system configuration for workpiece measurement. [Figure 3] 1 is a schematic diagram of the tool side part of the system structure for tool measurement. [Figure 4] FIG. 2 shows a measurement nozzle in which a tactile sensor is assigned as an axial actuator for fine-tuning the axial position of the measurement nozzle relative to the carrier. [Figure 5] FIG. 10 shows a schematic diagram of an arrangement for measuring the axial position of the side of the upper grinding wheel. [Figure 6] FIG. 1 shows two possibilities for spatially resolved position measurement of a workpiece surface with multiple measurement points. [Figure 7] FIG. 1 shows two possibilities for spatially resolved position measurement of a workpiece surface with multiple measurement points. [Figure 8A] FIG. 10 is a diagram for explaining measurement value evaluation. [Figure 8B] FIG. 10 is a diagram for explaining measurement value evaluation. [Figure 8C] FIG. 10 is a diagram for explaining measurement value evaluation. [Figure 8D] FIG. 10 is a diagram for explaining measurement value evaluation. [Figure 9] FIG. 10 is a path time diagram of non-contact approach control. [Figure 10] FIG. 10 is a schematic overview showing time-dependent distance values ​​and values ​​relating to the feed of the grinding wheel during a grinding operation. [Figure 11A] FIG. 10 shows a schematic gradient representing the time dependence during a grinding operation. [Figure 11B] FIG. 10 shows a schematic gradient representing the time dependence during a grinding operation. [Figure 11C] FIG. 10 shows a schematic gradient representing the time dependence during a grinding operation. [Figure 12] FIG. 1 is a diagram showing the relationship between wear and grinding ratio (G value). DETAILED DESCRIPTION OF THE INVENTION

[0057] 1 shows a schematic side view of an exemplary embodiment of a grinding machine 100 designed to grind substantially plane-parallel annular workpiece surfaces O1, O2 on disk-shaped workpiece portions of workpieces WS1, WS2 in the form of brake discs WS1, WS2. In the exemplary embodiment, the grinding machine is configured to grind the surfaces of annular braking portions BA on both sides of a coated brake disc.

[0058] Each brake disc has a main body, for example made of grey cast iron, with a central hub portion NA, which serves to secure the brake disc to the vehicle axle, and an annular braking portion BA surrounding the hub portion. The mass distribution of the main body is rotationally symmetrical as a whole with respect to the axis of rotation of the brake disc. The braking portion has two axially opposite, parallel surfaces (upper workpiece surface O1 and lower workpiece surface O2).

[0059] These are provided with a coating or functional layer in an upstream stage of the manufacturing process that is rotationally symmetrical with respect to the axis of rotation, the free surface of which is intended to ultimately serve as the friction surface of the brake disc. The coating can be extremely hard, for example, and contains tungsten carbide, titanium carbide, and / or niobium carbide. In the case of the examples, both sides were coated with the aid of a variant of the very high speed laser deposition welding, also known as the "EHLA method." The coating can also be applied by other methods, such as high velocity oxygen fuel (HVOF) or cold gas spraying.

[0060] The grinding machine 100 is configured as a numerically controlled rotating machine having two work stations, specifically a loading station 110 for loading and unloading, and a grinding station 120. All functions are realized via control commands from a motion control system control unit 190, which can be located locally (on or next to the machine) or remotely, for example in another room, and which in the example can operate via an operating unit 195 with an associated display and graphical user interface.

[0061] To transport the brake discs between the work stations 110, 120, an internal machine transport system is used which comprises a rotary table or turntable 150 which is mounted on or within the machine base 102 so as to be rotatable about a vertical turntable axis 152 and which can rotate unlimitedly about the turntable axis with the help of a rotary drive 105.

[0062] On the left side of FIG. 1 is a loading station 110. Here, a first brake disc (WS1 in this case) is received on the workpiece spindle 154 horizontally, i.e. with its axis of rotation oriented vertically ("record player arrangement"). Loading can be performed, for example, by a robot or any other handling device, or manually. Fixing can be performed, for example, via a clamp in place on the workpiece holding device or workpiece receiver 155 of the workpiece spindle, with the brake disc clamped in place for co-rotation so that its axis of rotation is coaxial with the axis of rotation 156. The brake disc can also be connected to the workpiece spindle by being pressed down or held from above. In an embodiment, a vertically movable pressing means 158 is provided.

[0063] The brake disc thus loaded is then transferred to a working position 125 in the area of ​​the grinding station 120 by rotating the rotary table 180° clockwise. Here, one or more of the grinding operation steps described below are carried out fully automatically. At the loading station 110, the previously completely ground brake disc can be simultaneously removed and a new, unground brake disc can be clamped in place. After grinding is complete, the brake disc, now completely ground on both sides, is rotated 180° and transferred to the loading station 110, from where it can be unloaded, for example, by a robot or other handling device or manually. The new brake disc to be ground can then be clamped onto the free workpiece spindle; apart from the exchange time, both workpiece spindles are occupied by brake discs, each in a different handling phase.

[0064] The grinding machine processes the surface of the workpiece by a double-sided grinding process. In the grinding station 120, the grinding machine 100 has a grinding unit 121 with two tool spindles (upper tool spindle 132-1 and lower tool spindle 132-2) ideally arranged coaxially with one another on a frame part, each carrying a grinding wheel (upper grinding wheel 130-2 and lower grinding wheel 130-2). The grinding wheels have abrasive side faces 135-1 and 135-2 facing each other and are arranged so that their grinding surfaces axially define a grinding space 133. Each grinding wheel is rotatable about its associated rotational axis 136-1 and 136-2 independently of the other grinding wheels by its associated spindle or rotary drive (upper rotary drive 134-1 and lower rotary drive 134-2), and can be fed or advanced by its own feed drive (upper feed drive 131-1 and lower feed drive 131-2) at a definable feed rate profile parallel to its associated rotational axis.

[0065] The grinding wheels 130-1, 130-2 are in the form of cup wheels having circumferentially segmented, individually replaceable and individually adjustable strip-like grinding segments.

[0066] One peculiarity of the grinding machine 100 is that it has two integrated position measurement systems, the results of which can be linked together and jointly evaluated to control the operation of the grinding machine.

[0067] The grinding machine has a first position measuring system 200, which is designed to determine, in the course of a non-contact distance measurement, workpiece position data representative of the axial position of the workpiece surfaces O1, O2 to be ground of the braking part BA (upper and lower faces) in at least one face position relative to the machine-based reference coordinate system RKS. The associated hardware parts (including distance sensors S1-1 and S2-1 in the form of measurement nozzles of the air measurement system) are arranged in the region of the working position 125 of the workpiece spindle in the processing zone of the grinding station 120, but outside the grinding space 133.

[0068] Also arranged in the area of ​​the grinding station 120 are hardware components of a second position measuring system 300, which is designed to determine tool position data representative of the axial positions of the opposing grinding flanks 135-1, 135-2 of the two grinding wheels relative to the same reference coordinate system RKS in the course of non-contact distance measurements. Tool-proximate hardware parts (including distance sensors S1-2 and S2-2 in the form of measuring nozzles of a pneumatic measuring system) are arranged in the grinding space 133.

[0069] The "axial position" of a surface in this case is the position of the surface at the measurement position in the axial direction, which in this case corresponds to the Z direction of the reference coordinate system RKS. In an ideally configured grinding machine, the rotation axes of the workpiece spindle 154 and the tool spindles 136-1, 136-2 are oriented parallel to the axial direction. The feed or advance movement of the grinding wheel is performed in the axial direction.

[0070] The first position measuring system 200 may also be referred to as a workpiece position data measuring system 200 , and similarly, the second position measuring system 300 may also be referred to as a tool position data measuring system 300 .

[0071] The measurement results of the two position measuring systems are jointly processed in an evaluation unit, which is a functional component of the control unit 190 and can be realized by corresponding evaluation software. Since the position data relating to the workpiece and the position data relating to the tool are present on the same computing system RKS, the spatial relationship between the abrasive sides 135-1, 135-2 of the grinding wheels and the associated workpiece surfaces O1, O2 can be determined by computing at any time.

[0072] In the illustrated configuration, the two position measuring systems are designed as pneumatic distance measuring systems. The distance sensors used are each measuring nozzles that, during operation, spray compressed air in the direction of the surface to be measured. A measurement signal is measured from the properties of the compressed air, which depend on the distance between the measuring nozzle and the surface, and is evaluated to determine the distance.

[0073] In the grinding machine of FIG. 1, the grinding station 120 simultaneously functions as a workpiece measurement station. The first position measurement system 200 comprises (at least) one upper measurement nozzle S1-1 and (at least) one lower measurement nozzle S2-1. The upper measurement nozzle S1-1 has a nozzle opening facing downward and is mounted to measure the distance from the upper side O1 of the braking portion BA. The lower measurement nozzle S2-1 is mounted with a nozzle opening facing upward and measures the distance from the lower portion O2 of the braking portion BA. Each sensor is movable in an automatically controlled manner within the associated working area both radially and axially relative to the rotation axis 156 of the workpiece spindle. Each sensor is further assigned an axial position actuator for fine-tuning the axial position of the respective measurement nozzle relative to the carrier (see FIG. 4).

[0074] In the second position measuring system 300, a similar arrangement is provided for measuring the tool, where the upper sensor S1-2 and the lower sensor S2-2 are respectively mounted with nozzle openings radially opposite each other in the region of the grinding space 133 between the grinding sides 135-1, 135-2, in particular so that the grinding sides of the cutting strip or grinding body are measured at the cup rim.

[0075] The grinding machine also has an internal calibration system with reference elements for calibrating and adjusting the distance sensors. The first position measurement system 200 has a reference element RE1 located in the lateral range of movement of the measurement nozzles S1-1 and S2-1. On each side (upper and lower), the reference element has two parallel planar measurement surfaces separated by a step, whose absolute positions in the reference coordinate system RKS are known with high precision. Similar reference elements RE2-1 and RE2-2 are provided on the opposite side for calibrating the tool-side measurement nozzles and distance sensors S1-2 and S2-2.

[0076] 2 (workpiece measurement) and 3 (tool measurement) show schematic diagrams of the system structure with the relevant components and parameters. The upper surface of the workpiece receiver 155, on which the inner surface of the hub portion NA rests, serves as the base for supporting the brake disc and in this case defines the axial reference level or axial reference A of the reference coordinate system RKS. All distances (axial distances) are related on the Z axis to this reference A. The basic idea of ​​the measurement method implemented in the grinding machine is based on the fact that the distances recorded by the sensors are always recorded relative to reference A. All measurement signals determined in the distance measurement and the data derived therefrom are available to the central control system or control unit 190 for offsetting.

[0077] With the help of the workpiece-side reference element RE1 and the tool-side reference elements RE2-1 and RE2-2, the pneumatic distance sensor can cooperate with the reference A. Since each reference element has two planar measurement surfaces that are offset from each other in the Z direction and have a defined distance in the axial direction, it is also possible to calibrate the measurement sensor using these reference elements.

[0078] The non-contact sensors (distance sensors) S1-1, S1-2, etc. formed by the measurement nozzles of the air pressure measurement system are mechanically coupled to tactile sensors ST1-1, ST1-2, etc. More precisely, the measurement nozzles are each fixed to an axially adjustable probe member of the tactile sensor. This coupling is shown diagrammatically in FIG. 4. This configuration offers advantages, in particular, regarding the extension of the measurement range (due to the axial displacement of the measurement nozzle over a relatively large travel distance), calibration, and the possibility of adjusting the axial position of the measurement nozzle. This configuration thus comprises a tactile distance sensor mechanically coupled to a non-contact distance sensor (measurement nozzle).

[0079] This combination of two sensors is advantageous for various applications, but can also be implemented in several other embodiments, for example in combination with a reference plate and a single measurement by an external measurement system, which also ensures metrological traceability of the measurement results.

[0080] The structure and function of the sensors are the same on the tool side and the workpiece side. The difference is that in this case the measurement nozzles S1-2 and S2-2 are arranged in different directions (nozzle openings facing away from each other). Therefore, on the tool side there is an upper reference element RE2-1 and a lower reference element RE2-2.

[0081] In the case of non-contact pneumatic distance measurement, i.e., the distance between the measurement sensor and the measurement surface is recorded by the sensor, the distance from the sensor to the measurement surface is recorded without contact. Figure 5 shows, by way of example, the situation in the area of ​​the sensor S1-2 for measuring the axial position of the flank 135-1 of the upper grinding wheel 130-1. Similarly, the axial position of the flank of the lower grinding wheel is measured.

[0082] The non-contact distance sensor (measuring nozzle) is movably mounted and can be moved via the associated machine axis in the Z direction (axial) and the orthogonal X direction (radial to the workpiece rotation axis) to assume different working positions. Different working positions of the same sensor S1-1 are shown in Figure 2. Working position P1 corresponds to a first reference position for calibration and / or adjustment at a first flattened reference surface of reference element RE1. Position P2 corresponds to a second position for calibration / adjustment at a further axially offset position. Position P3 indicates measurement of the upper workpiece surface O1 for distance recording in the process and upstream measurements (e.g., as part of input inspection). Position P4 is a reference position for comparison with a workpiece reference (reference A). The reference is redundant for protection and checking.

[0083] It is clear that in this case several geometric variables can be used on the workpiece side and on the tool side. All distances shown are known to the central control system 190 and can be stored digitally, for example, in a memory accessible to the control unit. Some values ​​can be generated from measurements with the aid of external measuring systems or by operator input. Another group of measurements are those from the built-in sensors. These include both the non-contact sensors Sx of the position measuring system (measuring nozzle) and the tactile sensors STx used for its axial displacement. Furthermore, measurements from the actuator systems are also included, for example from the encoders of the drives of the machine axes.

[0084] In this way, with the help of the first position measuring system 200 and the second position measuring system 300, workpiece position data (axial position of the surface to be ground on the braking part) and tool position data (axial position of the abrasive side of the grinding wheel relative to the same reference coordinate system) can be recorded as needed and made available to the evaluation unit. The two position measuring systems operate simultaneously in phases. The evaluation unit evaluates the generated data and processes it so that the control unit 190 can control the supply of the grinding wheel and / or other grinding parameters 130-1, 130-2 during different phases depending on these workpiece and tool position data. An overall high measurement accuracy is also advantageous in that measurements can be performed on a workpiece already in the working position 125 near the grinding wheel.

[0085] Several examples of useful modes of operation are described in the following text.

[0086] In one operating mode, the grinding machine can perform an input inspection of a newly loaded workpiece to be ground. To record the input quality of a new workpiece, the workpiece (brake disc) is first inserted and held, then transported from the loading station to the working position 125 of the grinding station 120. There, it is rotated once at a defined peripheral speed. The angular position of this rotation is recorded by the rotary encoder signal of the rotary drive for rotating the workpiece. The workpiece receiver 155 is equipped with an anti-rotation mechanism so that it has a defined zero position known to the control unit. The current workpiece position can be evaluated by comparing it with a reference disc or reference. The sequence begins with a calibration of the ideal reference. In this process, all distance values ​​are recorded along with the position reference for the angular position, as well as the X distance (radial distance from the rotation axis 156) and Z distance (axial distance) and saved in a reference matrix. The workpiece is then input and compared with the reference. As a result, relevant geometric characteristics of the brake disc, such as its circumferential warpage, can be evaluated and optionally taken into account in subsequent processes.

[0087] Similarly, after completion of the grinding process at grinding station 120, an output inspection of the fully ground workpiece can be performed. The workpiece measurements are compared to a reference value. Optionally, the reference disk can be measured again to provide a comparison value.

[0088] In each of these measurements, workpiece position data, i.e., the local axial positions of the workpiece surface, are recorded in a spatially resolved manner for multiple surface locations (or measurement points) in order to generate a sufficient amount of measurement data for assessing quality, both in the circumferential and radial directions. Figures 6 and 7 show two possible measurement schemes diagrammatically. In the variant of Figure 6, only one distance sensor S1-1 is used, which is gradually moved radially from the inside to the outside or from the outside to the inside during the rotation of the workpiece WS1. As a result, the measured measurement position MO lies on a spiral path. In the case of a tight spiral, the results are optionally circularly interpolated.

[0089] Alternatively, a sensor can be used that moves continuously to different radial positions and remains stationary while the workpiece rotates. In this case, the measured surface positions or measurement points MO are located on concentric circles, with their radial spacing selected according to the desired radial spatial resolution. The X-resolution of this method is variable and depends only on the size of the measurement spot for each individual measurement.

[0090] It is also possible to arrange multiple orientation sensors radially across the track width of the brake disc, either regularly or irregularly (see Figure 7). In this case, only one rotation of the workpiece is required. In this case, the radial resolution depends on the distribution interval and the measurement spot.

[0091] Possible result evaluations are explained with reference to Fig. 8, where Fig. 8A shows a schematic illustration of position referencing, and Fig. 8B shows the signal paths of the different sensors S1, S2, S3 during a 360° rotation U, with time plotted on the x-axis and axial position or distance values ​​ABZ plotted on the y-axis. Fig. 8C shows the offset of the measurements relative to the zero degree position P0, and Fig. 8D shows the corresponding offset for different positions Pi. The reference SP denotes the radial track width covered by the three sensors.

[0092] Each distance sensor has a well-defined position in a reference coordinate system at a given time t. The X position (radial position relative to the workpiece rotation axis) is a constant position for each distance sensor in this example. The Y position varies during rotation (rotation angle RW) and is generated by an angle encoder on the rotary drive for rotating the workpiece. This is converted into a Cartesian coordinate value. The Z position corresponds to the measured sensor distance and represents the workpiece position data. In this way, a measurement point related to its position on the workpiece is obtained for each sensor as a function of time.

[0093] A quality check evaluation or processing is carried out, for example, to check whether the measured value for each angular position is within the allowable tolerance range between an upper limit OGW and a lower limit UGW. Information about the input quality can be used to appropriately control the operation of the grinding machine during processing.

[0094] In a further operating mode, non-contact work approach control is implemented, which is explained in more detail by the path time diagram in Figure 9. In this case, before the start of the material-removal grinding operation on each side (top and bottom) (in phase P0), the grinding side of the grinding wheel is advanced, initially rapidly and at a slightly decreasing feed rate, to a workpiece-free position at a safe distance (e.g., 10 μm to 100 μm) in front of the workpiece surface to be ground. Proceeding from this starting position SP, in the next feed phase (phase P1), the tool is then fed at a reduced feed rate. This approach control is permissible in that the current position of the workpiece (Z position) and the current position of the tool are always known due to continuous distance measurements of the workpiece and the tool. Therefore, a rapid initial feed of both tools is possible simultaneously. In this case, the current axial position of the grinding side is recorded by non-contact distance measurement. The axial position of the workpiece side is already recorded for the first side as part of the input check.

[0095] The operator can now specify a safety distance within which the grinding flank can be fast-forwarded before switching from the fast-forward speed to the downside. In this case, the switch from phase P0 (fast-forward speed) to phase P1 (advancement to workpiece contact and subsequent material removal) is based on non-contact recorded measurements permanently recorded by a sensor. In phase P1, which begins after reaching the starting point SP with the safety distance, further advancement of the device can be regulated via the control device 190.

[0096] In stage P0, the tool and tool spindle are in their basic position. The tool and workpiece rotate in the process. Then, the two tools (upper and lower grinding wheels) move simultaneously towards the workpiece. Since the axial position of the workpiece surface is known and measurable, and the axial position of the axial flank is permanently known by measurement, the distance between the workpiece surface and the grinding flank can be determined at any time, and the starting position SP with a safety distance can be approached with high precision.

[0097] When switching to the P1 phase, the desired value of the safety distance for switching to the P1 phase is known to the machine control through operator input. The safety distance is, for example, on the order of about 10 μm to about 100 μm. The start point SP of phase P1 can therefore be determined from the operator input and measurements of the current shape of the workpiece and the tool position. Figure 9 shows a schematic path-time diagram of a possible velocity profile of the feed motion in the context of approach control. The switch point between phase P0 and phase P1 occurs when the defined safety distance is reached. This is the start point SP of the programmed control.

[0098] Compared to conventional approach control, which relies on physical contact between the workpiece surface and the tool, non-contact work approach control offers significant advantages. If the feed rate is rapidly increased until contact is achieved between the rotating tool and the rotating workpiece, significant material removal occurs immediately after the abrasive flank of the tool engages the workpiece, resulting in significant tool wear. This is particularly true when machining the extremely hard coatings found on brake discs. Non-contact approach control allows for rapid feed until contact is achieved, but contact is achieved a short time later, when the feed rate and corresponding wear rates are significantly reduced, thereby avoiding this situation, which would otherwise be particularly severe, without significantly slowing down the entire process.

[0099] Particularly when grinding the extremely hard coatings of brake discs, tool wear is a significant cost factor. Thanks to the position information available in real time and recorded by the position measurement system, a grinding method with particularly low tool wear can be achieved. There are also advantages with regard to wear compensation. As a result of the described approach control, the axial position of the abrasive grain is known just before the start of the material removal process, so compensation at this point is already realized.

[0100] During grinding, the axial position of the workpiece spindle and the distance between the tool and the workpiece can be recorded and evaluated so that information about tool wear can be derived from it at any time. For example, to determine the current coating height of the abrasive grains on the grinding wheel, the original coating height after setup can be entered into the control device by the operator. During processing, the positions of the machine axes used for feeding and the distance between the tool and the workpiece are recorded so that the amount of wear can be directly calculated.

[0101] Further advantages arise in particular with regard to stopping the grinding process, phase switching during the grinding process, wear monitoring and optionally wear compensation, and the possibility of determining real-time information on process-specific wear rates and thus optimizing the process sequence, as will be explained in particular with reference to Figures 10 to 12.

[0102] During the approach phase and material removal grinding, the distance sensor is constantly active and records, in particular, time-dependent processes, i.e., time-dependent distance values.

[0103] Some of the relationships that are useful for understanding are explained with reference to FIG. 10, which shows, in a schematic diagram, the time dependence of several parameters during the grinding operation. For this purpose, time t is plotted on the x-axis, and the value of the parameter ABZ, which indicates the axially measured distance between the distance sensor and the workpiece surface observed by it, is plotted on the y-axis. In the example, the sensor is sensor S2-1, which measures the distance from the underside of the braking part BA outside the grinding space. This distance increases as more material is removed from this underside. The horizontal line ABS represents a specific distance value that exists when the final dimension defined for the axial position of the brake disc underside is reached.

[0104] The process or grinding operation goes through a series of stages, with stage P0 being the start-up stage. Stage P1 is the first stage in which the grinding tool advances at a pre-programmed first feed rate. Stage Pn follows stage P1 after a programmed changeover time and is performed with a lower feed rate until the final dimension is reached. After completion of the first stage, there may be one or more successive stages with different grinding parameters.

[0105] First, the workpiece is placed on the workpiece receiver and pressed down firmly by the pressing means. This can result in a change in distance. The pressing down establishes a fixed relationship with the machine-based reference coordinate system. This is followed by an approach phase in which there is still no contact between the tool (grinding wheel) and the workpiece surface. Therefore, in this phase P0, the distance is constant (apart from periodic fluctuations in the ripples due to azimuthal waviness of the workpiece). The first phase (phase P1) begins in this example when workpiece contact is established. It is clear that in the first phase, the distance (apart from superimposed waviness) shows a continuous increase (one or more). After switching to the next phase Pn at the switching point UP, the distance increases less rapidly, resulting in less material removal per unit time. This material removal leads to a stop point AP.

[0106] This variant of stopping can proceed so that the operator first defines a part-dependent dimension. The defined dimension is converted into a value corresponding to the distance at the sensor. The grinding machine executes a running program continuously during grinding. In this case, the position measurement system becomes the master that decides the switchover between stages and the stopping at the end of the grinding process. The machine control therefore makes a decision regarding the stopping time or the time when the desired dimension has been reached based on the defining means and the measurements of the position measurement system.

[0107] A further possible way to obtain important information for controlling the grinding process occurs in some operating modes in that the time-dependent tool position data determined during the grinding operation are correlated with the time-dependent feed position data ZPOS. In other words, the evaluation can be expanded in that, in addition to the data resulting from the distance measurement, it is also possible to take into account data or values ​​that include the current axial position of each tool spindle.

[0108] Additional process-related information can be obtained, for example, if the distance measurements are offset with data representing the tool feed, i.e., the machine-side specifications for the Z position of the grinding wheel. This information can be obtained, for example, from the position encoder signals of the feed drives 131-1, 131-2 or from the control program. In this case, the time dependence of material removal or distance values ​​and feed can be specified, for example, in the form of a gradient. In FIG. 10, gradient line ST1 corresponds to the gradient of distance ABZ during phase P1. This can correspond, for example, to a material removal rate in the range of approximately 2 μm / s to approximately 5 μm / s. The lower material removal rate after switching to phase n, which can be, for example, on the order of approximately 1 μm / s, is represented by gradient line ST2, which has a lower gradient.

[0109] For the same time window, time-dependent data can be determined correspondingly for the programmed feed of the grinding wheel and the distance between the sensor of the second position measuring system 300 and the respective measured tool side (to determine tool position data). For illustrative purposes, FIG. 11 shows three path-time diagrams: FIG. 11A represents the measured value of the workpiece-side sensor system SSWS or its change over time, the central diagram (FIG. 11B) represents the gradient resulting from the programmed feed rate ZPOS of the tool, and the right diagram (FIG. 11C) represents the change over time of the distance ABZ of the second position measuring system (of the tool-side sensor system SSWZ). From the ratio of these gradients, important conclusions about the grinding process can be drawn.

[0110] As already mentioned above, the gradient line ST1 represents the change in the distance between the sensor S2-1 and the underside of the workpiece over time and should therefore substantially represent the material removal from the underside of this workpiece. If the currently programmed feed rate corresponds to a line with the same gradient, this (ideally) means that the entire forward movement is converted into workpiece removal without losses, which corresponds to a grinding process without wear of the grinding body.

[0111] However, in more realistic cases, the feed rate (center diagram, Z axis ZA) tends to be greater than the material removal rate achievable thereby. For illustrative purposes, a gradient line ST3 is also plotted in Figure 10, and the gradient of this line is much greater than the gradient (gradient line ST1) resulting from observing the distance values ​​over time. This discrepancy may have at least two different causes: tool wear and deformation.

[0112] In principle, the grinding body wears at one or more rates, so that only a portion of the feed movement is actually converted into material removal in the z-direction, while another portion compensates for the material wear. As an exemplary limiting case, one can consider a grinding process in which the mechanical hardness of the surface of the workpiece to be ground is much greater than the hardness of the grinding body, so that virtually no material removal occurs despite the advance. In this case, the gradient of material removal is virtually zero, while the gradient of the feed becomes much larger due to the continuous advance.

[0113] A second cause of deviations in the slope between the measured distance values ​​and the change in feed position over time is the possible deformation of the grinding machine components. Although these should be constructed as rigidly as possible, some deflection is unavoidable. As a result, part of the force acting when feeding the grinding wheel is not used to remove material and can lead to deformation of the grinding unit components.

[0114] In the inventors' experience, the proportion of the discrepancy Δ due to wear is much greater than the proportion due to deformation, so that to a first approximation it is possible to draw conclusions about tool wear from the discrepancy between gradient line ST1 and gradient line ST3 (for feed).

[0115] In order to be able to determine the share of deformations, in some embodiments the grinding unit is provided with one or more deformation sensors which are able to measure the deformations of the unit consisting of the tool spindle and the grinding wheel on both sides so that the share of the mismatched deformations can be taken into account in the evaluation.

[0116] In another operating mode, the control unit is configured to determine and provide quantitative information regarding the current grinding ratio G (also referred to as the G-value). The grinding ratio G corresponds to the ratio of material removal to wheel wear in each case in volume units. The grinding ratio G therefore provides meaningful information regarding the nature of the current grinding process, particularly with regard to tool wear and grinding efficiency, or the ratio of material removal to tool wear. The grinding ratio allows the process to be described in terms of productivity and output. The grinding machine can directly calculate the grinding ratio (G-value) during operation using existing actuators, sensors, and operator inputs. The G-value and corresponding data can be displayed to the operator numerically and / or graphically in an appropriate manner. Alternatively or additionally, an alarm signal can be generated when the AC current significantly deviates or is about to deviate from a defined set value. Alternatively or additionally, adjustments can be made with the aid of the control unit, for example, to set the grinding operation so that the grinding ratio remains within a defined value range. To determine the G-value, in an embodiment, the following information is processed: G1: Total area of ​​cut strips | ASG or area of ​​individual strips G2: Coating height of cutting strip |BHs G3: Current axial position and / or current distance from the tool side of the sensor system G4: Track width of workpiece G5: Start height and current height of the upper / lower side of the workpiece

[0117] The current volume of the cutting strip VGS(t) can be determined from the area of ​​the cutting strip G5 and the height of the cutting strip (G2 / G3). The volume VGW(t) can be determined from the track width (ring area |G4) and the distance of the sensor system from the workpiece side (G5). The G value is determined by VGW(t) / VGS(t). As the wear VS (in volume units) decreases for a constant machining amount, the G value G increases. An example path is shown in Figure 12. As a result of these functionalities, the operator and / or the control are provided with the possibility to set the optimal grinding process for each machining task. [Explanation of symbols]

[0118] 100 Grinding Machine 121 Grinding Unit 130-1, 130-2 grinding wheels 131-1, 131-2 Feed drive unit 132-1, 132-2 Tool spindle 133 Grinding Space 134-1, 134-2 Rotation drive unit 135-1, 135-2 Polished side 136-1, 136-2 Rotating shaft 154 Workpiece spindle 155 Workpiece receiving section 156 Rotation axis 157 Rotational drive unit 190 Control Unit RKS Machine-Based Reference Coordinate System O1, O2 Workpiece surface WS1, WS2 processed products WA disc-shaped workpiece

Claims

1. A grinding machine (100) for grinding substantially planar annular workpiece surfaces on a disc-shaped workpiece portion (WA) of a workpiece (WS1, WS2), in particular for grinding the workpiece surfaces of the annular braking portion of a brake disc, comprising: a grinding unit (121) having two coaxially arranged tool spindles (132-1, 132-2) each supporting a grinding wheel (130-1, 130-2), the grinding wheels being arranged with opposing abrasive sides (135-1, 135-2) axially defining a grinding space (133), each of the grinding wheels being rotatable about an associated rotation axis (136-1, 136-2) independently of the other grinding disk by an associated rotation drive (134-1, 134-2) and feedable parallel to the associated rotation axis by a feed drive (131-1, 131-2); at least one workpiece spindle (154) having a workpiece receiving portion (155) for receiving the workpiece (WS1, WS2) for co-rotation, the workpiece receiving portion being rotatable by a rotary drive (157) about an axis of rotation (156) extending parallel to the axis of rotation of the grinding wheel, the at least one workpiece spindle (154) being arranged in a working position during at least one phase of the grinding operation such that a workpiece portion (WA) of the received workpiece extends in an arc through the grinding space; a motion control system having a control unit (190) for controlling the operation of the grinding machine; A grinding machine (100) comprising: a first position data determination system for determining workpiece position data representative of an axial position of the workpiece surface (O1, O2) at least one surface location relative to a machine-based reference coordinate system (RKS); a second position data determination system for determining tool position data representative of the axial positions of the polishing sides (135-1, 135-2) facing the workpiece surfaces (O1, O2) relative to the same reference coordinate system (RKS); is characterized by The control unit (190) is configured to control, in at least one operating mode, at least one grinding parameter in at least one stage of the grinding operation in response to the workpiece position data and / or the tool position data.

2. The control unit (190) selects, depending on the workpiece position data and / or the tool position data, one of the following groups: grinding wheel feed rate; grinding wheel speed; the speed of the workpiece spindle carrying the workpiece for the grinding operation; A rotational direction of the workpiece spindle that carries the workpiece for the grinding operation. configured to control at least one grinding parameter from 2. A grinding machine according to claim 1.

3. the first position data determination system is in the form of a first position measurement system (200) for metrologically determining the workpiece position data and the second position data determination system is in the form of a second position measurement system (300) for metrologically determining the tool position data in the same reference coordinate system (REF), preferably the first position measurement system (200) and / or the second position measurement system (300) are position measurement systems operating without contact; 3. A grinding machine according to claim 1 or 2.

4. the first position measuring system (200) is configured to measure the workpiece (WS2) when installed in the workpiece receiving section (155), preferably configured such that position measurements can be made when the workpiece receiving section (155) with the workpiece is in a working position (125); 4. A grinding machine according to claim 3.

5. the first position measurement system (200) and the second position measurement system (300) are configured to be able to perform position measurements when the workpiece receiver with the workpiece is in the working position, and preferably the grinding machine (100) is configured to simultaneously measure workpiece position data and tool position data during at least one stage of a grinding operation.

5. A grinding machine according to claim 3 or 4.

6. the first position measuring system (200) and / or the second position measuring system (300) are in the form of a distance measuring system for measuring the distance between at least one distance sensor (Sx) of the position measuring system and the surface to be measured, preferably the distance measuring system being a pneumatic measuring system having a distance sensor in the form of a measuring nozzle (Sx); 6. The grinding machine according to claim 3, wherein the grinding machine is a grinding machine having a plurality of grinding members.

7. the grinding machine has an internal machine calibration system with reference elements (REx) for calibrating the sensors, in particular the distance sensors (Sx), preferably the distance sensors are movable in a controlled manner within their respective working areas, each distance sensor being assigned a reference element (REx) which is located within the working area of ​​the distance sensor and accessible for reference measurements, and / or the reference element has, on its side accessible for distance measurements, a first measuring surface and at least one second measuring surface, the measuring surfaces being located at different axial positions; 7. The grinding machine according to claim 3, wherein the grinding machine is a grinding machine having a plurality of grinding members.

8. 8. Grinding machine according to claim 6 or 7, characterized in that one distance sensor, preferably each distance sensor (x), is assigned an axial actuator (STx) for controllably varying the axial position of the distance sensor and / or one distance sensor, preferably each distance sensor, is assigned an axial position encoder for sensing the axial position of the distance sensor, preferably one distance sensor, preferably each distance sensor, comprises a measuring nozzle of a pneumatic measuring system, the measuring nozzle being fixed to an axially movable probe element of a tactile sensor.

9. The grinding machine (100) is in the form of a multi-station grinding machine; The multi-station grinding machine a transport system having a spindle carrier unit (150) movable relative to a machine base (102) and supporting at least one workpiece spindle (154), the at least one workpiece spindle (154) being mounted so as to be rotatable about a rotation axis (156) relative to the spindle carrier unit and having a workpiece receiving portion (155); at least two work stations (110, 120) accessible by the workpiece spindle and including a loading station (110) and at least one grinding station (120) equipped with at least one grinding unit (121); Equipped with Preferably, the spindle carrier unit has at least one spindle carrier unit which is rotatable like a turntable or which is translatable and which can be reciprocated between the loading station and the working station on the grinding unit. A grinding machine according to any one of claims 1 to 8.

10. the control unit (190) is configured in one operating mode to perform an input inspection of the workpiece to be ground by measuring the workpiece in the grinding machine, and after the workpiece has been fixed in the workpiece receiver and before the start of the grinding operation, workpiece position data are determined on the workpiece, preferably in a spatially resolved manner for a plurality of circumferentially offset surface positions and / or a plurality of radially offset surface positions, for each surface of the workpiece portion to be ground, and in particular workpiece shape data are determined from the workpiece position data. A grinding machine according to any one of claims 1 to 9.

11. the control unit (190) is configured in one operation mode to perform a non-contact work approach control, wherein, when feeding in the direction of the workpiece surface to be ground, the abrasive side of the grinding wheel is fed to a range of a start position (SP) located at a safe distance from the workpiece surface to be machined, and to determine the start position (SP), initial workpiece position data and initial tool position data are offset from each other, and preferably the grinding wheel is fed at a first feed rate until the start position (SP) is reached, and upon reaching the start position, the feed rate is automatically reduced to a lower second feed rate, and preferably the second feed rate is maintained at least until the current tool axial position reaches a nominal contact position corresponding to the initial workpiece axial position. A grinding machine according to any one of claims 1 to 10.

12. the control unit (190) is configured in one operating mode such that tool position data is determined continuously or intermittently as a function of time during the grinding operation, and the resulting time-dependent tool position data is processed to control the feed of the grinding wheel and / or at least one other grinding parameter. A grinding machine according to any one of claims 1 to 11.

13. The control unit (190) is configured in one mode of operation to correlate time-dependent tool position data determined during the grinding operation with time-dependent feed position data. A grinding machine according to any one of claims 1 to 12.

14. The control unit (190) is configured, in one mode of operation, to determine information about a current grinding ratio G, defined as the ratio between material removal in volume units and wheel wear; Preferably, the target grinding ratio desired for the grinding process or the parameters necessary to determine the target grinding ratio are definable, and the control unit uses data provided by sensors to calculate the current grinding ratio permanently or at short intervals and compare it with the target grinding ratio, in particular by the following means: generating an alarm signal, in particular an electrical, acoustic, optical and / or tactile alarm signal, when the current grinding ratio is outside a tolerance range around the target grinding ratio or is approaching a tolerance limit at a certain rate of change and a limit breach is imminent; adjusting the grinding operation to maintain a desired target grinding ratio so that the grinding operation proceeds within approximately a desired tolerance of the target grinding ratio without operator intervention; and controlling operation of the grinding machine in response to the result of the comparison using one of A grinding machine according to any one of claims 1 to 13.

15. 1. A grinding method for grinding substantially planar annular workpiece surfaces on a disc-shaped workpiece portion, in particular for grinding the surface of an annular braking portion of a brake disc, using a grinding machine having two grinding wheels with opposing abrasive sides that axially define a grinding space of variable height, comprising: the grinding wheels are rotatable independently of one another about coaxial axes of rotation and are feedable by advancing in an axial direction parallel to the axes of rotation; the workpiece is received in a workpiece receiving portion rotatable about a rotation axis so as to be co-rotatable with the workpiece, and is arranged in a working position at least during the grinding operation so that a portion of the workpiece extends in an arc through the grinding space; To perform a grinding operation, the workpiece and the grinding wheel are set to rotate about an axis of rotation, and the abrasive side is brought into engagement with the associated workpiece surface by axial feeding of the grinding wheel; The grinding method comprises, for each workpiece surface to be ground: determining workpiece position data indicative of an axial position of a workpiece surface being ground at at least one surface location relative to a reference coordinate system; determining tool position data representing the axial position of an abrasive side facing said workpiece surface relative to the same reference coordinate system; controlling at least one grinding parameter of the grinding operation in response to the workpiece position data and / or the tool position data in at least one stage; A grinding method comprising:

16. a preferably contactless distance measurement is performed between a distance sensor and the workpiece surface to be measured in order to determine the workpiece position data and / or the tool position data, and preferably a pneumatic measurement system is used for the distance measurement, which has at least one measurement nozzle acting as a distance sensor.

16. The grinding method according to claim 15.

17. the workpiece (WS2) is measured in a state where it is installed in the workpiece receiving section (155), in particular when the workpiece receiving section (155) with the workpiece is placed in the working position (125); 17. The grinding method according to claim 15 or 16.

18. In one mode of operation, input inspection of the workpiece to be ground is performed by measuring the workpiece in the grinding machine, and after the workpiece is fixed in the workpiece receiver and before the start of the grinding operation, workpiece position data is determined on the workpiece for each of the surfaces of the workpiece portion to be ground.

18. A grinding method according to claim 15, wherein:

19. the spatially resolved determination of workpiece position data is characterized in that workpiece position data is determined for a plurality of circumferentially offset surface locations and / or a plurality of radially offset surface locations, and preferably workpiece shape data is determined from said workpiece position data, in particular a thickness of said workpiece portion between said mutually substantially parallel workpiece surfaces, a curvature of said workpiece portion in a radial direction, and / or a waviness in a circumferential and / or radial direction. The grinding method according to any one of claims 15 to 18.

20. In one operating mode, a non-contact work approach control is performed, in which, when feeding in the direction of the workpiece surface to be ground, the abrasive flank of the grinding wheel is fed rapidly to the extent of a start position (SP) located at a safe distance from the workpiece surface to be machined, and when said start position is reached, the feed rate is automatically reduced to a lower second feed rate, said safe distance being definable, in particular in the range of 10 μm to 100 μm; The grinding method according to any one of claims 15 to 19.

21. During at least one stage of the grinding operation, workpiece position data and tool position data are measured simultaneously; The grinding method according to any one of claims 15 to 20.

22. during operation of the grinding machine, the distance sensor is suitably calibrated by a reference element placed in the working area of ​​the distance sensor of a machine internal calibration system and, optionally, adjusted by controlled variation of the axial position of the distance sensor; 212. A grinding method according to any one of claims 15 to 211.

23. During the grinding operation, tool position data is determined continuously or intermittently as a function of time, and the time-dependent tool position data is processed to control the feed of the grinding wheel. The grinding method according to any one of claims 15 to 22.

24. In one mode of operation, time-dependent tool position data determined during the grinding operation is correlated with time-dependent feed position data. The grinding method according to any one of claims 15 to 23.

25. In the evaluation mode, a grinding ratio G is determined, and preferably at least one grinding parameter of the grinding process is controlled in response to the grinding ratio G. The grinding method according to any one of claims 15 to 24.

Images