Clamping device, especially machine vice

Abstract

Clamping device (1) for carrying out a clamping operation, in particular for clamping a component in the clamping device (1), in particular as a machine vice (1) for clamping a workpiece, with a) a rotatably mounted spindle (5), the spindle (5) generating a linear clamping force (F) depending on its rotational position, and b) a measuring device (13-19) for measuring a stress state of the clamping device (1), wherein the measured stress state is a measure of the generated linear clamping force (F), characterized in that c) that the measuring device (13-19) measures the stress state of the spindle (5), in particular by measuring the longitudinal extension of the spindle (5).

Description

Technical field of the invention

[0001] The invention relates to a clamping device for carrying out a clamping operation, in particular for clamping a component in the clamping device, for example as a machine vice for clamping a workpiece. Background of the invention

[0002] Machine vices for clamping workpieces are known from the prior art (e.g. DE 10 2018 122 635 B3, DE 10 2022 133 100 A1, DE 20 2016 000 989 U1, WO 2025 / 031566 A1). The linear clamping force acting on the workpiece to be clamped is generated by a screw spindle that is rotatably mounted in a base body of the machine vice and generates the linear clamping force depending on its rotational position. For this purpose, the screw spindle is axially fixed in the base body of the machine vice and engages with its ends in movable vice slides, whereby the screw spindle forms a screw drive with each of the two vice slides. The clamping force is measured by a measuring device that measures a stress state in the base body of the machine vice or in the spindle bearing.

[0003] However, this well-known method of determining the clamping force is associated with various disadvantages.

[0004] On the one hand, only the reaction forces that are introduced into the base body of the machine vice or into the spindle bearing during a clamping process are absorbed.

[0005] On the other hand, the vice slides change their position during a clamping process, so that the relationship between the measured stress state in the base body or in the spindle bearing on the one hand and the linear clamping force on the other hand is not constant during a clamping process. Description of the invention

[0006] The invention is therefore based on the object of creating a correspondingly improved clamping device.

[0007] The clamping device according to the invention has, in accordance with the known machine vices described above, a rotatably mounted spindle (e.g. screw spindle), wherein the spindle generates a linear clamping force depending on its rotational position, for example by means of a screw drive.

[0008] Furthermore, the clamping device according to the invention, in accordance with the known machine vices described above, also has a measuring device which measures a mechanical stress state of the clamping device, wherein the measured stress state is a measure of the generated linear clamping force.

[0009] In contrast to the known machine vices described above, the measuring device in the clamping device according to the invention not only measures the reaction forces that are introduced into the base body of the machine vice or into the spindle bearing during a clamping process. Instead, the measuring device in the clamping device according to the invention measures the stress state of the spindle (e.g., screw spindle) itself, in particular by measuring the longitudinal expansion of the spindle. Firstly, this measuring principle according to the invention is more precise. Secondly, this measuring principle is also independent of the respective position of the vice slides, which varies during a clamping process.

[0010] In one variant of the invention, the measuring device has at least one stationary measuring sensor that measures the stress state of the spindle (e.g. screw spindle) and outputs a corresponding output signal that reflects the stress state of the spindle. For example, this stationary measuring sensor can be arranged on the outside of the lateral surface of the rotating spindle and measure the magnetic flux density in the spindle, whereby the magnetic flux density changes depending on the stress state in the spindle. Depending on the design of the measuring arrangement, further variables can be recorded (e.g. distance, tilt, etc.). For example, this stationary measuring sensor can be an inductive sensor (e.g. eddy current sensor). The term "stationary" used in the context of the invention refers to the base body of the machine vice, i.e.In this variant of the invention, the measuring sensor is stationary with respect to the base body of the machine vice.

[0011] In another variant of the invention, however, the measuring device has at least one measuring sensor (e.g., strain gauge) rotating with the spindle, which measures the stress state of the spindle and outputs a corresponding output signal that reflects the stress state of the spindle. For example, this measuring sensor rotating with the spindle can be mounted on the outer surface of the spindle or inside the spindle.

[0012] In a preferred embodiment of the invention, the measuring device has a plurality of measuring sensors, for example two or four (strain gauge measuring bridge) measuring sensors, which measure the stress state of the spindle (e.g. screw spindle) at different axial positions along the spindle.

[0013] In the preferred embodiment of the invention, the clamping device is a machine vice (e.g. centering vice) for clamping a workpiece. Machine vices of this type are sufficiently known from the prior art and therefore need not be described in detail. At this point, it should only be mentioned that the machine vice according to the invention has a base body with a spindle bearing for rotatably supporting the spindle in the base body, wherein the rotatable spindle is designed as a screw spindle. In addition, the machine vice according to the invention has at least one vice carriage which is slidably guided in the base body and is displaced by the screw spindle in accordance with the rotational position of the screw spindle.

[0014] When the machine vice is designed as a centering clamp, two vice slides are provided, both of which are slidably guided in the base body and are moved by the screw spindle in accordance with the rotational position of the screw spindle relative to the base body, in opposite directions.

[0015] Another option is the floating clamp (compensating clamp) design. The floating clamp (compensating clamp) design is essentially identical to the centering clamp, but the spindle bearing can be moved within certain limits to compensate for tolerances when using multiple vices to clamp large or long workpieces.

[0016] In a design of the machine vice according to the invention as a fixed jaw clamp, however, only a single movable vice slide is provided, which is moved by the screw spindle according to the rotational position of the screw spindle and carries one clamping jaw, while the other clamping jaw is fixedly mounted on the base body.

[0017] Furthermore, the machine vise according to the invention has two clamping jaws for clamping the component, with the two clamping jaws being movable relative to each other. In the above-described design as a centering clamp, the two clamping jaws are arranged on two movable vice slides and are thus both displaced. In the above-described design as a fixed-jaw clamp, however, one of the two clamping jaws is fixed in place, while the other clamping jaw is movable.

[0018] Furthermore, it should be noted that the measuring device preferably has a stationary evaluation unit connected to the at least one measuring sensor and evaluating the output signal of the sensor to determine the clamping force acting on the component to be clamped. Thus, the measured deformation of the spindle (e.g., screw spindle) does not usually directly reflect the linear clamping force. Rather, a conversion is usually required, which is performed by the evaluation unit.

[0019] It was already mentioned above that the measuring sensor (e.g. strain gauge) can be arranged on the spindle and rotates with the spindle. To query the rotating measuring sensor, a signal transmitter is preferably provided, which is connected to the rotating measuring sensor wirelessly, contactlessly, or with contact, and is connected to the stationary evaluation unit via a connecting cable or wirelessly (e.g. via Bluetooth or WLAN). The wireless connection between the signal transmitter on the one hand and the rotating measuring sensor (e.g. strain gauge) on the other hand can be established via sliding contacts or inductively, to name just two examples.

[0020] Furthermore, it should be mentioned in general that the stationary evaluation unit is preferably arranged in the base body or on the base body of the machine vice.

[0021] In the preferred embodiment of a machine vice according to the invention, the screw spindle is rotatably mounted centrally or eccentrically in a spindle bearing and axially fixed, so that the screw spindle protrudes on both sides of the spindle bearing and generally engages in the two movable vice slides, forming a screw drive there in each case. In one variant of the invention, the measuring device has at least one measuring sensor on each side of the spindle bearing, which measures the stress state of the screw spindle on both sides of the spindle bearing. In another variant of the invention, however, a single measuring sensor is provided, which measures the stress state of the screw spindle centrally or eccentrically in the spindle bearing.

[0022] Furthermore, it should be generally mentioned that the measuring device preferably has a power supply with an electrical energy storage device, in particular a rechargeable battery, which enables mains-independent operation of the clamping device according to the invention. However, this is not mandatory. The power supply can also be wired.

[0023] Furthermore, it should be mentioned in general that the machine vice according to the invention can optionally be designed as a centering clamp, a compensating clamp or a fixed jaw clamp, as already mentioned above.

[0024] Furthermore, it should be noted that the machine vise according to the invention can be designed either as an internal clamp or as an external clamp. With the external clamp design, the component to be clamped is clamped internally between the two clamping jaws, so that the clamping force acts inward on the component to be clamped. With the internal clamp design, however, the component to be clamped encircles the clamping jaws, so that the clamping force acts outward on the component to be clamped.

[0025] It was already mentioned above that the screw spindle is preferably axially fixed in the base body of the machine vice. For this purpose, two annular collars can be formed on the outside of the screw spindle. In one variant of the invention, the spindle bearing engages between the two collars on the screw spindle in order to fix the screw spindle axially in the base body of the machine vice. In another variant of the invention, however, the spindle bearing engages around the two collars on the screw spindle in the axial direction on the outside in order to fix the screw spindle axially in the base body. This variant of the invention still offers space in the axial direction between the two collars for a measuring sensor.

[0026] Instead of the collars mentioned above, the spindle bearing can also be designed with a single collar or instead with grooves arranged in the outer surface of the screw spindle.

[0027] In general, it should also be mentioned that the screw spindle can be one-piece or multi-piece.

[0028] In addition, the evaluation unit can have a microcontroller.

[0029] It should also be mentioned that the evaluation unit can perform various actions depending on the determined tension state, such as switching a drive of the screw spindle, switching on an indicator light or a visual representation of the clamping force.

[0030] Finally, it should be noted that the invention is not only applicable to the preferred embodiment of a machine vise. Rather, the technical teaching of the invention can also be used generally in clamping devices in which a rotary motion of a spindle is converted into a linear clamping force. The invention can therefore also be used, for example, in screw drives, threaded spindles, ball screws, or high-speed lifting gears (bevel gear lifting gears). The term "clamping device" used in the context of the invention is therefore to be understood in a general sense.

[0031] Other advantageous developments of the invention are characterized in the subclaims or are explained in more detail below together with the description of the preferred embodiments of the invention with reference to the figures. Brief description of the drawings Fig. 1 shows a cross-sectional view of a machine vice according to the invention, which is designed as a centering clamp and external clamp. Fig. 2 shows a representation of the screw spindle of the machine vice from Fig. 1 with two stationary measuring sensors for measuring the clamping force on the screw spindle. Fig. 3 shows a modification of Fig. 2 with four strain gauges on the screw spindle to determine the clamping force, whereby only two strain gauges are visible. Fig. 4 finally shows a modification of Fig. 2, with a single sensor located centrally on the screw spindle. Detailed description of the drawings

[0032] In the following, the Fig. 1 and Fig. 2, the embodiment of a machine vice 1 according to the invention is described, which is designed as a centering clamp and external clamp, as is known per se from the prior art.

[0033] For this purpose, the machine vice 1 initially has a base body 2 in which two vice slides 3, 4 are movably guided, as indicated by the double arrows.

[0034] The movement of the vice slides 3, 4 during a clamping process is achieved by a screw spindle 5, which is rotatably mounted in a spindle bearing 6 in the base body 2 of the machine vice 1 and axially fixed. The rotational drive of the screw spindle 5 is not shown and can be, for example, electric motor-driven, pneumatically driven, hydraulically driven, or manually driven, as is known in the art.

[0035] For axial fixing of the screw spindle 5 in the base body 2 of the machine vice 1, two collars 7, 8 are formed on the outside of the screw spindle 5, which engage around the spindle bearing 6 in the axial direction and thereby fix the screw spindle 5 axially in the base body 2 of the machine vice 1.

[0036] The screw spindle 5 has an external thread 9, 10 at each of its two ends, which forms a screw drive with the two vice slides 3, 4, so that a rotation of the screw spindle 5 leads to a corresponding counter-rotating linear displacement of the two vice slides 3, 4 in the direction of the double arrows. The axial fixation of the screw spindle 5 in the spindle bearing 6 results in the component to be clamped being clamped centrally in the machine vice 1, which is why the machine vice 1 in this design is also referred to as a centering clamp.

[0037] A clamping jaw 11, 12 is screwed onto the top of each of the two vice slides 3, 4 in order to clamp the workpiece, whereby the workpiece is not shown for the sake of simplicity.

[0038] In addition, the machine vice 1 has two measuring sensors 13, 14 (e.g., eddy current sensors) that are fixedly arranged in the base body 2 of the machine vice 1 and, during a clamping process, measure the stress state of the screw spindle 5 on both sides of the spindle bearing 6. In this embodiment, the fixed measuring sensors 13, 14 are eddy current sensors, as known, for example, from DE 10 2021 103 803 A1.

[0039] The two measuring sensors 13, 14 each generate an output signal that represents the tension state of the screw spindle 5 and transmits this output signal to an evaluation unit 15, which calculates the linear clamping force F that is applied to the workpiece by the clamping jaws 11, 12.

[0040] In addition, an accumulator 16 is shown, which serves to supply power to the evaluation unit 15, wherein the accumulator 16 can be arranged, for example, in the base body 2 of the machine vice 1 and enables mains-independent operation.

[0041] The embodiment according to Fig. 3 partly corresponds to the above-described and Fig. 1 and Fig. 2, so that in order to avoid repetition, reference is made to the above description, the same reference numerals being used for corresponding details.

[0042] A special feature of this embodiment is that the two measuring sensors 13, 14 are not arranged in a fixed location. Instead, the two measuring sensors 13, 14 are strain gauges that are attached to the outside of the casing surface of the screw spindle 5 and measure the mechanical stress state (e.g. longitudinal strain) of the screw spindle 5. The two measuring sensors 13, 14 therefore rotate with the screw spindle 5 during operation. It should be noted that only the two measuring sensors 13, 14 are visible in the drawing. However, on the opposite side of the screw spindle 5 there are two further strain gauges that are not visible in the drawing. In total there are therefore four strain gauges attached to the screw spindle 5.

[0043] A further special feature of this embodiment is that two signal transmitters 17, 18 are provided to connect the rotating measuring sensors 13, 14 on the one hand and the stationary evaluation unit 15 on the other hand, which can contact the two measuring sensors 13, 14, for example via slip rings.

[0044] The embodiment according to Fig. 4 partly corresponds to the above-described and Fig. 1 and Fig. 2, so that in order to avoid repetition, reference is made to the above description, the same reference numerals being used for corresponding details.

[0045] A special feature of this embodiment is that only a single measuring sensor 19 is arranged in a fixed position, namely between the two collars 7, 8, which are formed on the outside of the lateral surface of the screw spindle 5.

[0046] A further special feature of this embodiment is that the spindle bearing has two parts 6.1, 6.2, which engage around the two collars 7, 8 on the screw spindle 5 in the axial direction and thereby fix the screw spindle 5 axially in the base body 2 of the machine vice 1.

[0047] The invention is not limited to the preferred embodiments described above. Rather, the invention also encompasses variants and modifications that also utilize the inventive concept and therefore fall within the scope of protection. In particular, the invention also claims protection for the subject matter and features of the subclaims, independent of the respective claims referred to, and in particular even without the features of the main claim. The invention thus encompasses various aspects of the invention that enjoy protection independently of one another. Advantages of the invention

[0048] The invention provides for measuring the tension state of the screw spindle directly at the screw spindle, as opposed to measuring the tension state on the base body of the machine vice. On the one hand, this offers the advantage that the clamping force measurement is not dependent on the position of the movable vice slides. On the other hand, this measuring principle is also significantly more accurate than measuring the tension state by measuring the tension state in the base body of the machine vice. List of reference symbols 1 machine vice as centering clamp and external clamp 2 Base body of the machine vice 3, 4 vice slides 5 screw spindle to drive the vice slides 6 Spindle bearing for axial fixation of the screw spindle in the base body 6.1, 6.2 Parts of the spindle bearing 7, 8 collars on the screw spindle for axial fixation of the screw spindle in the base body of the machine vice 9, 10 External thread of the screw spindle for moving the vice slides by means of a screw drive 11, 12 clamping jaws on the sliding vice slide 13, 14 Sensor (eddy current sensor in Fig. 1, Fig. 2, Fig. 4 or strain gauges in Fig. 3) 15 Evaluation unit for calculating the linear clamping force 16 accumulator for power supply 17, 18 Signal transmitter for connecting the evaluation unit with the rotating measuring sensors 19 Sensor in the spindle bearing QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2018 122 635 B3

[0002] DE 10 2022 133 100 A1

[0002] DE 20 2016 000 989 U1

[0002] WO 2025 / 031566 A1

[0002] DE 10 2021 103 803 A1

[0038]

Claims

[1] Clamping device (1) for carrying out a clamping operation, in particular for clamping a component in the clamping device (1), in particular as a machine vice (1) for clamping a workpiece, with a) a rotatably mounted spindle (5), the spindle (5) generating a linear clamping force (F) depending on its rotational position, and b) a measuring device (13-19) for measuring a stress state of the clamping device (1), wherein the measured stress state is a measure of the generated linear clamping force (F), characterized by , c) that the measuring device (13-19) measures the stress state of the spindle (5), in particular by measuring the longitudinal extension of the spindle (5). [2] Clamping device (1) according to claim 1, characterized by , a) that the measuring device (13-19) has at least one stationary measuring sensor (13, 14) which measures the stress state of the spindle (5) and outputs a corresponding output signal which represents the stress state of the spindle (5), b) that the stationary measuring sensor (13, 14) is preferably arranged on the outside of the lateral surface of the rotating spindle (5), c) that the measuring sensor (13, 14) preferably has an inductive sensor, in particular an eddy current sensor. [3] Clamping device (1) according to claim 1, characterized by , a) that the measuring device (13-19) has at least one measuring sensor (13, 14) rotating with the spindle (5), which measures the stress state of the spindle (5) and outputs a corresponding output signal which represents the stress state of the spindle (5), b) that the measuring sensor (13, 14) is preferably mounted on the outer surface of the spindle (5) or in the spindle (5), c) that the measuring sensor (13, 14) preferably has a strain gauge. [4] Clamping device (1) according to one of the preceding claims, characterized by that the clamping device (1) is a machine vice (1), in particular a centering clamp, with the following components: a) a base body (2), b) a spindle bearing (6) in the base body (2) for rotatably supporting the spindle (5), which is designed as a screw spindle (5), in particular in the center of the screw spindle (5), c) at least one vice slide (3, 4) which is displaceably guided in the base body (2) and is displaced by the screw spindle (5) in accordance with the rotational position of the screw spindle (5), and d) two clamping jaws (11, 12) for clamping the component, wherein the two clamping jaws (11, 12) are displaceable relative to one another. [5] Clamping device (1) according to one of the preceding claims, characterized by that the measuring device (13-19) has a stationary evaluation unit (15) which is connected to the at least one measuring sensor (13, 14) and evaluates the output signal of the at least one measuring sensor (13, 14) in order to determine the clamping force (F) acting on the component to be clamped. [6] Clamping device (1) according to claim 5, characterized by , a) that the at least one measuring sensor (13, 14) is arranged on or in the spindle (5) and rotates with the spindle (5), b) that the evaluation unit (15) is connected to the at least one measuring sensor (13, 14) via a signal transmitter (17, 18), c) that the signal transmitter (17, 18) is, on the one hand, wirelessly connected to the at least one measuring sensor (13, 14) rotating with the spindle (5), in particular via sliding contacts or inductively, and d) that the signal transmitter (17, 18) is connected to the stationary evaluation unit (15) via a connecting cable or wirelessly. [7] Clamping device (1) according to one of claims 5 or 6, characterized by that the stationary evaluation unit (15) is arranged in the base body (2) or on the base body (2) of the machine vice (1). [8] Clamping device (1) according to one of claims 4 to 7, characterized by , a) that the screw spindle (5) is rotatably mounted centrally in a spindle bearing (6) and is axially fixed so that the screw spindle (5) protrudes to both sides of the spindle bearing (6), and b) that the measuring device (13-19) b1) has at least one measuring sensor (13, 14) on each side of the spindle bearing (6), which measures the stress state of the screw spindle (5) on both sides of the spindle bearing (6), or b2) has a measuring sensor (13, 14) which measures the stress state of the screw spindle (5) centrally or off-center in the spindle bearing (6). [9] Clamping device (1) according to one of the preceding claims, characterized by that the measuring device (13-19) has a power supply (16) with an electrical energy store (16), in particular with a rechargeable accumulator (16). [10] Clamping device (1) according to one of claims 4 to 9, characterized by , that a) that the machine vice (1) is a centering vice or a floating vice, in which the two vice slides (3, 4) are both displaceable in the base body (2) by the screw spindle (5), or b) that the machine vice (1) is a fixed jaw clamp in which one of the two clamping jaws (11, 12) is fixed in place on the base body (2) of the machine vice (1), while the vice slide (3, 4) with the other clamping jaw can be moved by the screw spindle (5). [11] Clamping device (1) according to one of claims 4 to 10, characterized by , a) that the machine vice (1) is an external clamp, in which the component to be clamped is clamped internally between the two clamping jaws (11, 12) so that the clamping force (F) acts inwards on the component to be clamped, or b) that the machine vice (1) is an internal clamp in which the component to be clamped engages around the clamping jaws (11, 12) so that the clamping force (F) acts outwards on the component to be clamped. [12] Clamping device (1) according to one of claims 4 to 11, characterized by , a) that two collars (7, 8) are formed on the outside of the screw spindle (5) in order to fix the screw spindle (5) axially, b) that the spindle bearing (6) b1) engages between the two collars (7, 8) on the screw spindle (5) in order to fix the screw spindle (5) axially in the base body (2), or b2) engages around the two collars (7, 8) on the screw spindle (5) in the axial direction on the outside in order to fix the screw spindle (5) axially in the base body (2). [13] Clamping device (1) according to one of claims 4 to 12, characterized by , a) that the screw spindle (5) is one-piece or multi-piece, and / or b) that the evaluation unit (15) has a microcontroller, and / or c) that the evaluation unit (15) carries out at least one of the following actions depending on the determined voltage state: c1) Switching off a drive of the screw spindle (5), c2) Switching on an indicator light, c3) visual representation of the clamping force (F), or c4) Transfer of the clamping force (F) to a higher-level process control.

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