Grinding device for rolling bodies and method for determining the filling of a grinding device

Abstract

The invention relates to a grinding device (1) for rolling bodies (2), in particular balls, comprising at least one grinding disc (3, 4), which is designed to grind rolling bodies (2) guided in at least one track (10) of the grinding disc (3, 4). Furthermore, an evaluation system (14) is provided, which is designed to acoustically detect the rolling bodies (2) guided through the track (10) individually and to determine the filling degree (FG) of the track (10) in turn.

Description

TECHNICAL FIELD

[0001] The invention relates to a device for grinding rolling bodies, in particular balls. Furthermore, the invention relates to a method for determining the filling level of a grinding device. BACKGROUND

[0002] Such a grinding device for grinding balls is known, for example, from DE 7 410 301 U. The known grinding device has two horizontally arranged rotatable discs between which an abrasive and the bodies to be ground, i.e. the rolling bodies, are added. One of the two discs of the known grinding device is composed of a hard material, while the other disc is provided with a layer composed of a rubber-elastic material. The first disc made of a hard material, for example oxide ceramic, has guide grooves for guiding the bodies to be ground, which can describe a helical shape. The axes of rotation of the two discs can overlap or be offset from one another. With the device according to DE 7 410 301 U, in particular grinding of balls composed of a hard material or oxide ceramic should be possible.

[0003] A further device for grinding ceramic balls is described in EP 1 893 384 B1. In this case, the use of a grinding disc with abrasive grains in a synthetic resin bond is proposed, wherein more than 50% of the abrasive grains are composed of diamond. In the sense of a reasonable process, the ball feed should take place by means of a reservoir. For loading and unloading the balls, a single ball inlet and outlet is provided. As in the device according to DE 7 410 301 U, in the device according to EP 1 893 384 B1, too, the grinding disc is arranged horizontally.

[0004] Ball grinding machines with vertically arranged grinding discs, i.e. with a horizontal axis of rotation, are also known from the prior art, for example from the document DE 193953 A. Likewise, grinding machines with obliquely arranged grinding discs, which are designed for machining rolling bodies, are described in the prior art. Reference is made in this regard, for example, to the documents US 5,301,470 A and WO 96 / 33047 A1. SUMMARY

[0005] The invention is based on the object of further improving the grinding of rolling bodies with respect to the proposed prior art, wherein, under the conditions of mass production, an especially high process reliability with only very small fluctuations in the product parameters is sought.

[0006] The object is achieved according to the grinding device of the invention. Likewise, the object is achieved by the method for determining the filling level of a grinding device according to the invention. In the following, the design solutions and advantages set forth below in connection with the method for determining the filling level according to the invention are meaningfully applicable to the device for grinding rolling bodies, and vice versa.

[0007] The grinding device comprises at least one grinding disc which constitutes a track for grinding rolling bodies, in particular balls, which are guided in the track of the grinding disc. Furthermore, the grinding device comprises an evaluation system which constitutes an acoustic detection of the rolling bodies guided through the track, i.e. which are discharged from the grinding device, in order to determine the filling of the track. The filling of the track, through which the rolling bodies pass during grinding, is also referred to as the filling of the grinding device.

[0008] The present application is based on the consideration that the parameters of the workpiece, i.e. the rolling bodies, are significantly related to the filling of the grinding device. The theoretical upper limit of the filling is 100%, which means that the grinding gap is completely filled with rolling bodies. In order to achieve a uniform and targeted material removal of the workpiece, the filling should be set to a defined value below 100%. It is in principle possible to derive the filling only by theoretical considerations. The input variables of such considerations are the geometrical features of the grinding device and of the workpiece to be ground, by means of which the movement state of the workpiece in the grinding device can be simulated. The filling very greatly influences the forces acting on the workpiece.

[0009] Based on the considerations, a semi-theoretical method for determining the filling of a grinding device is proposed, which has the following features:

[0010] - providing a grinding disc arrangement having a rolling body inlet, a rolling body outlet and at least one track for the rolling bodies to be ground, which is delimited by at least one grinding disc,

[0011] - filling the rolling bodies into the rolling body inlet and grinding the rolling bodies,

[0012] - discharging the ground rolling bodies from the rolling body outlet,

[0013] - acoustically detecting each rolling body discharged from the rolling body outlet as it falls onto a receiving body,

[0014] - determining the filling of the grinding disc arrangement from the time intervals between the detected acoustic signals associated with each rolling body, respectively, on the basis of the known average dwell time of the rolling bodies when grinding in the grinding disc arrangement and the known total length of the at least one track to be traversed by the rolling bodies when grinding and the dimensions of the rolling bodies.

[0015] In particular, the filling is determined by means of the following formula:

[0016] FG = (VwD / dt) x (DW / LR), wherein

[0017] FG = filling of the grinding device,

[0018] VwD = average dwell time of the rolling bodies in the grinding disc arrangement,

[0019] dt = measured average time interval between two signals showing the drop of a rolling body, DW = rolling body diameter,

[0020] LR = total length of at least one track available for the rolling body to traverse in the grinding device.

[0021] The number of events, respectively representing the exit of a processed rolling body from the grinding device, can be detected, for example, in a fixed, sliding time period, in terms of the average time interval between two acoustic signals. Alternatively, the number of events, for example 10 or 20 events, can be preset, wherein the time period elapsed during the events is measured.

[0022] To eliminate possible interfering background signals, the acoustic signals can be processed by means of filtering, in particular high-pass filtering. Low-pass filtering or band filtering can also be considered. To detect the acoustic signals generated by the dropping rolling bodies, solid-borne sound sensors are particularly suitable. With regard to solid-borne sound sensors, reference is made, for example, to the documents DE 10 2007 057 136 A1, DE 42 07910 C2 and WO 2014 / 095763 A1.

[0023] The grinding device can be operated by means of a single rotating disc or by means of a plurality of rotating discs. The total rotational speed can be taken into account in the degree of filling determination.

[0024] In an advantageous design, the receiver, in particular the measuring plate, is supported at a damping element, in particular a support. The damping element is designed such that it has a particularly high attenuation in the frequency generated by the impacting rolling bodies. The solid-borne sound sensors can be mounted directly at the receiver, in particular below the measuring plate.

[0025] At least one grinding disc of the grinding device is arranged horizontally in a typical design. Likewise, vertical arrangements of the grinding discs or inclinations of their rotational axes are considered, as is known in theory from the prior art.

[0026] Irrespective of the arrangement of the one or more grinding discs in space, different constructional possibilities exist, which relate to the geometry of at least one track to be traversed by the rolling bodies. For example, a plurality of tracks are nested concentrically in one another. Alternatively, the individual tracks in which the rolling bodies are ground are configured in a helical shape. BRIEF DESCRIPTION OF DRAWINGS

[0027] In the following, embodiments of the application are explained in detail with reference to the drawings. Shown here is:

[0028] Figure 1 a schematic side view of a grinding device,

[0029] Figure 2 a flow chart of a method which can be performed by means of the grinding device,

[0030] Figure 3 Another schematic view of the grinding apparatus is shown. DETAILED DESCRIPTION

[0031] The grinding apparatus, which is designated as a whole by the reference numeral 1, is configured as a horizontal grinding machine and is provided for machining rolling bodies 2, i.e. balls for ball bearings. The grinding apparatus 1 comprises a grinding table device 5 which is configured by two grinding tables 3, 4, which are also referred to as grinding machines in a narrower sense. The grinding tables 3, 4 have grooves 6, 7 in which the balls 2 are ground. A rolling body inlet of the grinding table device 5 is designated by 8 and a rolling body outlet is designated by 9. A common median axis of the grinding tables 3, 4 is designated by MA.

[0032] In Figure 3 The angle a which is formed between the rolling body inlet 8, the median axis MA and the rolling body outlet 9 is plotted in the diagram in Fig. 1. During grinding, the rolling bodies 2 which are fed through the rolling body inlet 8 typically pass several revolutions before they leave the grinding table device 5 at the rolling body outlet 9. Overall, an orbit 10 is formed by the grooves 6, 7, which is available for the rolling bodies 2 to traverse in the grinding table device 5 and which has a total length LR. The number of rolling bodies 2 which are simultaneously in the grinding table device 5 multiplied by the rolling body diameter DW results in the length of an imaginary chain of rolling bodies 2 which are arranged in contact with each other. The ratio of the length of the chain to the total length LR is the fill degree FG of the grinding table device 5, which is also referred to as the fill degree FG of the grinding apparatus 1.

[0033] A direct measurement of the fill degree FG is in principle possible in that the rolling bodies 2 which are fed through the rolling body inlet 8 and the rolling bodies 2 which leave from the rolling body outlet 9 are counted individually, wherein the time instants of the rolling body entry and exit are also detected.

[0034] In the present case, however, no counting of the rolling bodies 2 is provided on the entry side of the grinding table device 5. Instead, the counting of the rolling bodies 2 on the exit side, which is also discussed in detail below, is combined with data relating to the rolling body traversal through the grinding table device 5. In relation to the data, theoretical considerations of the construction and dimensions of the grinding apparatus 1 as well as the rolling bodies 2 are combined with experimental observations. From the basic construction of its geometry, the grinding table device 5 has a commonality with axial ball bearings. Based on one fixed grinding table 3, 4 and the rotation of the other grinding table 4, 3, each rolling body 2 rotates around the median axis MA with an angular velocity which is approximately half the speed which the rotating grinding table 3, 4 has. Differently thereto, inter alia based on the fact that the rolling bodies 2 not only pointwise contact the grinding tables 3, 4 and can be detected experimentally and / or simulated by other theoretical considerations. Finally, therewith the average dwell time VwD is determined which states how long on average each rolling body 2 is in the grinding table device 5.

[0035] At the outlet 9 of the rolling bodies, the rolling bodies 2 are received by an evacuation belt 11. From the evacuation belt 11, the rolling bodies 2 fall individually onto a measuring plate 12, which is a receiving body. At the receiving body 12, there is a solid sound sensor 13, which belongs to an evaluation system 14. The receiving body 12 is supported as derived from Figure 1 by means of a damping element 15.

[0036] With regard to the functioning of the evaluation system 14, reference is made to Figure 2 . Subsequently, different data D1, D2, D3 are input into the evaluation system 14. Here, statistical data D1, dynamic data D2 and sensor data D3. Belonging to the statistical data D1 are, inter alia, the ball diameter DW and the overall length LR of the track 10. The dynamic data D2 comprise the rotational speed of the grinding discs 3, 4. This applies accordingly even when both grinding discs 3, 4 are rotating. As sensor data D3, which are obtained by means of the solid sound sensor 13, individual pulses are mentioned, which are generated by the rolling bodies 2 striking onto the measuring plate 12.

[0037] The evaluation system 14 determines the average time interval dt between two signals, which are respectively generated by the rolling bodies 2 falling onto the measuring plate 12. The time period in which the average time interval dt is determined can be set. Alternatively, the number of individual events, i.e. the detected sound pulses, can be set before the average value of the time intervals dt is formed.

[0038] In any case, a high-pass filter is used in order to avoid distortions of the signals received by the evaluation system 14. The average time interval dt is related to the average dwell time VwD of the rolling bodies 2 in the grinding disc arrangement 5. If the average time interval dt is, for example, one tenth of the average dwell time VwD, this indicates that on average ten rolling bodies 2 are simultaneously in the grinding gap between the grinding discs 3, 4. Furthermore, the overall length LR is derived, which in this example corresponds to 50 times the rolling body diameter DW.

[0039] The filling degree FG of the grinding device 1, more precisely of the grinding disc arrangement 5, is determined according to the following formula:

[0040] FG = (VwD / dt) x (DW / LR)

[0041] In this case, 10 x 1 / 50 = 20%. In order to set a changed filling degree FG, for example the rotational speed of the grinding discs 3, 4 or of the ball reservoir can be varied.

[0042] Legend of the drawing

[0043] 1 grinding device

[0044] 2 rolling body

[0045] 3 grinding disc

[0046] 4 grinding disc

[0047] 5 grinding disc device, grinding machine in a narrow sense

[0048] 6 recess

[0049] 7 recess

[0050] 8 rolling body inlet

[0051] 9 rolling body outlet

[0052] 10 track

[0053] 11 discharge belt

[0054] 12 measuring plate, receiver

[0055] 13 solid-state acoustic sensor

[0056] 14 evaluation system

[0057] 15 damping element

[0058] α angle

[0059] D1 statistical data

[0060] D2 dynamic data

[0061] D3 sensor data

[0062] dt average time interval

[0063] DW rolling body diameter

[0064] FG filling degree

[0065] LR total length of the track

[0066] MA median axis

[0067] VwD average dwell time

Claims

1. A grinding device (1) for rolling bodies (2), comprising at least one grinding disc (3, 4), which forms a track (10) for grinding rolling bodies (2) guided in the track (10) of the grinding disc (3, 4), characterized in that an evaluation system (14) is provided, which forms a means for acoustically detecting the rolling bodies (2) guided through the track (10) individually and determining the filling degree (FG) of the track (10).

2. The grinding device (1) according to claim 1, characterized in that a plurality of tracks (10) for rolling bodies (2) are formed by the grinding disc (3, 4), which are nested into one another.

3. The grinding device (1) according to claim 1, characterized in that a helical track (10) for rolling bodies (2) is formed by the grinding disc (3, 4).

4. The grinding device (1) according to any one of claims 1 to 3, characterized in that a solid-borne sound sensor (13) belonging to the evaluation system (14) is provided, which forms a means for acoustically detecting the falling of each rolling body (2) onto a measuring plate (12).

5. The grinding device (1) according to claim 4, characterized in that the measuring plate (12) is supported at a damping element (15).

6. The grinding device (1) according to any one of claims 1 to 3, characterized in that the grinding disc (3, 4) is arranged horizontally.

7. A method for determining the filling degree (FG) of a grinding device (1), the method having the following steps: - providing a grinding disc arrangement (5) having a rolling body inlet (8), a rolling body outlet (9) and at least one track (10) for rolling bodies (2) to be ground, which is delimited by at least one grinding disc (3, 4), - filling rolling bodies (2) into the rolling body inlet (8) and grinding the rolling bodies (2), - conducting the ground rolling bodies (2) out of the rolling body outlet (9), - acoustically detecting each rolling body (2) conducted out of the rolling body outlet (9) when it falls onto a receiver, - determining the filling degree (FG) of the grinding disc arrangement (5) from the time intervals (dt) between the detected acoustical signals associated with each rolling body (2), respectively, on the basis of the known average dwell time (VwD) of the rolling bodies (2) when grinding in the grinding disc arrangement (5) and the known total length (LR) of the track (10) to be traversed by the rolling bodies (2) when grinding and the dimensions of the rolling bodies (2).

8. The method according to claim 7, characterized in that the filling degree (FG) is determined by means of the following formula: FG = (VwD / dt) x (DW / LR), wherein VwD = the average dwell time of the rolling bodies (2) in the grinding disc arrangement, dt = the measured average time interval between two signals showing the falling of the rolling bodies (2), respectively, DW = the rolling body diameter, LR = the total length of the track (10). LR = total length of at least one track (10) available for the rolling bodies (2) to cross in the mill device (5).

9. The method according to claim 7 or 8, characterized in that the acoustic signal of the rolling bodies (2) impacting on the receiver is processed by means of a high-pass filter.

10. The method according to claim 7 or 8, characterized in that the filling degree (FG) is determined taking into account the rotational speed of the at least one mill (3, 4).

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