CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Application No. 10 2018 210 989.3, filed in the Federal Republic of Germany on Jul. 4, 2018, which is expressly incorporated herein in its entirety by reference thereto.

FIELD OF THE INVENTION

The present invention relates to a measuring device for a position measurement for spindles or rotary tables and to a component assembly for a spindle or for a rotary table including a corresponding measuring device.

BACKGROUND INFORMATION

The particular spindles or rotary tables are frequently used in machining equipment or machining centers. Spindles or motor spindles often hold a rotating tool such as a cutting tool in machine tools. Workpieces are fastened in place on rotary tables and then processed by machine cutting, for example. In addition, rotary tables are used in measuring machines, and a workpiece attached to the rotary table is measured in such equipment. Spindles or rotary tables of this type are frequently equipped with angle-measuring devices, which are used for measuring rotatory movements of a shaft. Angle-measuring devices are particularly used in machine tools or measuring machines for the purpose of measuring rotatory movements. There exists a growing demand for an increase in the performance of such spindles or rotary tables, in particular in the precision during the operation.

Japanese Patent Document No. 2010-217167 describes a measuring device having an encoder, with the aid of which a rotational frequency of a shaft can be measured and which also generates signals from which an axial loading of the shaft can be inferred.

SUMMARY

Example embodiments of the present invention provide a measuring device, which is suitable for a spindle or for a rotary table and which makes it possible to determine the position of an axis of rotation in multiple directions during an ongoing operation.

According to an example embodiment of the present invention, the measuring device is suitable for a spindle or for a rotary table and includes at least two first position sensing elements, at least two second position sensing elements, and a scale element, which has a first graduation or first scale and a second graduation or second scale. The scale element is arranged so as to be rotatable about an axis of rotation relative to the first and the second position sensing elements. The first graduation includes regular structures, which are arranged in parallel next to one another along a first direction, the first direction having a directional component in the circumferential direction. The second graduation includes regular structures, which are arranged in parallel next to one another along a second direction, the second direction having a directional component in the axial direction. The at least two first position sensing elements are disposed at an offset from one another in the circumferential direction, and the first graduation is scannable by the at least two first position sensing elements so that the position of the scale element in a plane that has an orthogonal orientation relative to the axis of rotation is able to be determined (and thus the position of the axis of rotation or an axle displacement under an operating load). In addition, an angular position of the scale element in relation to the first position sensing elements (e.g., relative to the position sensing elements) within and across a rotation is able to be determined in absolute terms by scanning the first graduation with the aid of at least one of the first position sensing elements. The at least two second position sensing elements are also disposed at an offset from one another in the circumferential direction, and the second graduation is able to be scanned by the second position sensing elements, and the axial position of the scale element (and thus an axle displacement in the axial direction under an operating load) is able to be determined.

The use of at least one of the first position sensing elements makes it possible to determine an angular position of the scale element in relation to the first position sensing elements in absolute terms within and across a rotation. For example, this is achievable by providing the first graduation with an absolute code track or else by applying a reference mark on the scale element, which, in conjunction with an incremental graduation, allows for an absolute determination of the angular position within a rotation.

The first direction along which the regular structures of the first graduation are situated next to one another may be identical to the circumferential direction. In the same manner, the first direction may be inclined or obliquely positioned (but not perpendicular to the circumferential direction) with respect to the circumferential direction. Similarly, the second direction along which the regular structures of the second graduation are disposed next to one another may be arranged identically to the axial direction (and thus parallel to the axis of rotation). In a similar manner, the second direction may extend at an incline or obliquely with respect to the axial direction (but not perpendicular to the axial direction). For example, regular structures of the first graduation and those of the second graduation may be oriented in the form of an arrow relative to one another.

The measuring device may have at least three first position sensing elements and at least three second position sensing elements.

The measuring device may have a circuit board on which at least one electronic component is secured in place. The first position sensing elements are electrically connected to the electronic component so that signals from the first position sensing elements are able to be processed by the electronic component. Alternatively or additionally, the second position sensing elements are electrically connected to the electronic component so that signals from the second position sensing elements are able to be processed by the electronic component. A processor or a microcontroller, in particular, may be provided as an electronic component.

The circuit board has, for example, an annular shape, e.g., a closed ring shape, in which the annular circuit board arranged as a closed ring that extends across 360°, an open ring shape, e.g., an open ring segment, for instance, that extends across at least 180°, and in particular across at least 270°, etc.

The first position sensing elements and the second position sensing elements may be electrically connected to the electronic component, and the angular position of the scale element, the position of the scale element in the plane perpendicular to the axis of rotation, and the axial position of the scale element may be able to be determined with the aid of the electronic component.

Tilting of the scale element, and thus tilting of the axis of rotation, may be determinable with the aid of the second position sensing elements. In particular, the at least two position sensing elements may be electrically connected to the electronic component, and the electronic component is able to determine the tilting of the scale element. It may be particularly beneficial in this context to use three or more second position sensing elements.

In the case of spindles or rotary tables, which by nature have a correspondingly stiff development, such tilting is relatively minor and lies in ranges of less than one angular minute relative to the ideal axis of rotation, e.g., 100 angular minutes down to 50 angular minutes. As a result, it is also the case that only minimal position changes are encountered due to such tilting, which means that the measuring device must have a very high resolution in order to provide reliable information or quantitative values in connection with the tilting. Since the axis of rotation may possibly rotate, the described tilting may lead to tumbling motions of the scale element, such tumbling motions being recordable in quantitative terms, especially also utilizing the measured angular position, with the aid of the measuring device.

A further sensor, by which accelerations or vibrations or temperatures are measurable, may be mounted on the circuit board. In particular, two or more further sensors may be mounted on the circuit board.

A memory component is fixed in place on the circuit board, which may be used as a data logger for storing information that is based on the signals generated by the first position sensing elements and/or the second position sensing elements and/or the further sensor.

The first position sensing elements and/or the second position sensing elements and/or the further sensor may be connected to the annular circuit board by flexible circuit boards.

The first position sensing elements and/or the second position sensing elements may include magnet sensors, and the structures of the first graduation and/or the second graduation may be arranged as magnetic poles. The first position sensing elements and/or the second position sensing elements may operate on the basis of a magnetoresistive principle, for example, or may be arranged as Hall-effect sensors. Alternatively, the measuring device may also be based on an optical or inductive measuring principle, and combinations of the principles are possible as well, with the result that the first graduation is able to be scanned using a principle that differs from that used for the second graduation.

The sensors of the first position sensing elements by which the first graduation is scannable may be disposed at an offset with regard to the axial direction from the sensors of the second position sensing elements by which the second graduation is scannable.

At least the second graduation (or both graduations) may be applied on a lateral side of a cylindrical scale element.

For example, an annular body, which is able to be fastened to a shaft, may be provided as a scale element. However, the first and/or the second graduation may alternatively also be directly applied to the shaft.

According to an example embodiment of the present invention, a component assembly for a spindle or for a rotary table has a measuring device, which includes a circuit board on which an electronic component is fixed in place, so that signals from the first and/or the second position sensing elements are able to be processed by the electronic component, the component assembly having a housing and the circuit board being enclosed by the housing.

The component assembly may include a shaft, a preloading element, and two bearings, arranged as rolling bearings. The scale element is mounted so as to be axially displaceable in relation to the shaft, and the bearings are axially preloaded with the aid of the preloading element such that the scale element is situated in the power flow of the axial preloading. Alternatively or additionally, the measuring device includes a measuring device housing, which is mounted in an axially displaceable manner with respect to the shaft, the bearings being axially preloaded with the aid of the preloading element such that the measuring device housing is arranged in the power flow of the axial preloading.

With the aid of the measuring device, axle displacements of a tool spindle, for example, are able to be detected online, the rotor temperature may be measured in a contact-free manner, imbalances and vibrations of the axis of rotation may be recorded, and information pertaining to operating states (max. temperature, max. vibrations, operating hours, etc.) are able to be stored over a longer period of time and output again. In particular based on the measured values of the angular position and the position of the scale element in the plane perpendicular to the axis of rotation (axle displacement), a correction of the setpoint position in the machining and/or measuring process is able to be performed through a numerical control. Thus, for example, a trajectory of a cutting tool, which is possibly clamped in a spindle, may be corrected during the machining of a workpiece. The measuring device may particularly be configured such that correction values are generated in the interplay with a numerical control, the correction values being based on the position data measured by the measuring device in conjunction with the absolute angle position.

For this purpose, the measuring device may, for example, provide a resolution of under 2 μm, in particular a resolution of less than 1 μm, especially less than 750 nm. These values for the resolutions are able to be achieved both for the determination of the axial and the lateral positions, that is to say, in the plane perpendicular to the axis of rotation.

Further features and aspects of example embodiments of the present invention are described in more detail below with reference to the appended Figures.

