Patent Publication Number: US-2021187684-A1

Title: Measuring system for monitoring a spindle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Phase of PCT Appln. No. PCT/DE2018/100861 filed Oct. 22, 2018, which claims priority to DE 10 2017 124 667.3 filed Oct. 23, 2017, the entire disclosures of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a measuring system for monitoring a spindle. 
     BACKGROUND 
     DE 103 48 608 B4 discloses a monitoring system for a spindle device, comprising a first sensor, for detecting a rotational speed of the spindle device, and a second sensor, for detecting a temperature of the spindle device. The monitoring system additionally includes a classifier means, by which the state of the spindle device is classified on the basis of the sensor data. An evaluation means is used to forecast a maintenance requirement of the spindle device, by means of a model, on the basis of the sensor data and of predetermined limit values and the classified condition. 
     EP 1 425 640 B1 describes a monitoring system for in-process monitoring of tools, workpieces or machining processes in chip-removing machine tools. The system comprises at least one sensor for the acquisition of measurement signals from the machining process, which are equated to at least one direction of force, a resultant force, a pressure, a torque, a motor power, a motor current, a vibration, an acceleration, a structure-borne noise or a change in distance between two machine parts. Another component of the system is a monitoring hardware, having software for storing and comparing monitoring data in tool-specific or cut-specific monitoring stages. In the case of measurement signals that breach predefined monitoring thresholds, appropriate actions are triggered. An operating hardware, with software, is used to operate or parameterize the monitoring system, or to visualize the measurement signals. 
     The so-called Spindle Condition Monitoring System (SpiCoM) for machine tool spindles is known from the company FAG Kugelfischer Georg Schafer AG. The main component of SpiCoM is a measuring ring, which can be integrated into the spindle and which contactlessly measures the relative displacements and tilts, in all spatial directions, between the shaft and housing. The measuring ring comprises an inner ring mechanically connected to the spindle, and an outer sensor ring fastened to the spindle housing. There are three radial and three axial eddy-current sensors, each offset by 120° in relation to each other, integrated into the sensor ring. The inner ring consists of a target ring, having axial and radial measuring surfaces, which is mounted on a steel carrier ring. 
     SUMMARY 
     It is desirable to provide an optimized measuring system for monitoring spindles, based on the known SpiCoM system, which is transferable to differing spindle diameters, which can be inexpensively integrated into machine tool spindles and which always achieves sufficient measuring accuracy. 
     The measuring system serves to monitor a spindle. It comprises, firstly, a cylindrical housing, which can be positioned in a spindle housing and can be mechanically connected to it in a fixed manner. Arranged within the housing is a carrier ring, which is mechanically connected to the housing in a fixed manner. The measuring system also includes three first sensors, for measuring a radial displacement of the spindle, and three second sensors, for measuring an axial displacement of the spindle. The first and second sensors are distributed over the circumference of the carrier ring. The sensors are encapsulated with the carrier ring. 
     A significant advantage of the measuring system is that, by encapsulating the sensors with the carrier ring, the sensors are optimally protected against environmental influences such as moisture, extreme temperature differences, and mechanical and chemical influences. The sensors positioned accordingly on the carrier ring are fixed in their position by the encapsulation, enabling small positioning tolerances to be achieved. The sensors are thus always in an optimum position, which ensures a sufficient measuring accuracy, of preferably 1 μm. In order to adapt to differing spindle diameters, housings and carrier rings having differing diameters, which can accordingly be combined with the sensors, may be kept available. 
     The measuring system may comprise at least one electronic module for the exchange of data and energy with the sensors. The at least one electronic module may also be encapsulated with the carrier ring, and is thus reliably protected against environmental influences. The electronic module may be connected to an external data processing unit. For embodiments that use several electronic modules, it has proven to be advantageous to distribute the electronic modules over the circumference of the carrier ring. The electronic modules may be connected to each other via flexible printed circuit boards. 
     The sensors may be realized as eddy-current sensors. In this context, it is expedient to further equip the measuring system with a first measuring ring having axial measuring surfaces, and with a second measuring ring having radial measuring surfaces. The two measuring rings can be mechanically connected to the spindle in a fixed manner. Furthermore, the measuring rings are dimensioned in such a manner that they can be arranged within the carrier ring, and the measuring surfaces can be sensed by the sensors. The measuring rings may be mechanically connected to each other in a fixed manner, such that they can easily be fastened as a unit to the spindle. Alternatively, the measuring rings may also be realized as a single component. 
     The housing may have an opening for feedthrough of a connection cable. The opening may be realized in such a manner that the connection cable can be fed through radially or axially. 
     The housing may be composed of metal. The connection cable may be connected to the housing in an electrically conductive manner, within the housing, via an electrically conductive seal. The electrically conductive seal may be realized, for example, as a textile seal or an elastomer seal. 
     According to an advantageous embodiment, a first sensor and a second sensor are in each case arranged in pairs. The sensor pairs in this case may be arranged with an offset of 120° in relation to each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The measuring system is explained in greater detail in the following, on the basis of the single FIGURE. The FIGURE shows an exploded representation of the measuring. 
     
    
    
     DETAILED DESCRIPTION 
     A measuring system  01  serves to monitor a spindle of a machine tool. It comprises, firstly, a cylindrical housing  02 , which may be composed of metal. The housing  02  is suitable for being arranged within a spindle housing. It can be mechanically connected to the latter in a fixed manner. There is an opening  03  made in the housing  02 . A connection cable  04  can be fed radially or axially through the opening  03 . 
     Within the housing  02 , following assembly, there is a carrier ring  05 , which may be composed of plastic. The carrier ring  05  is mechanically connected to the housing  02  in a fixed manner. Distributed over the circumference of the carrier ring  05  are three first sensors  07  and three second sensors  08 . There is a fixed mechanical connection between the carrier ring  05  and the sensors  07 ,  08 . The first sensors  07  serve to measure a radial displacement of the spindle, while the second sensors  08  are designed to measure an axial displacement of the spindle. The sensors  07 ,  08  may be realized as eddy-current sensors and/or vibration sensors and/or rotational-speed recognition sensors. A first sensor  07  and a second sensor  08  may be in each case combined in pairs. The sensor pairs are arranged with an approximately 120° offset in relation to each other. 
     The measuring system  01  is equipped with electronic modules  09  for exchanging data and energy with the sensors  07 ,  08 . The electronic modules  09  are connected to each other by means of flexible printed circuit boards  10 . They may be connected to an external data processing unit (not represented). 
     By means of an encapsulation  12 , the sensors  07 ,  08  and the electronic modules  10  are connected to the carrier ring  05 , in a permanent and mutually aligned manner. 
     The connection cable  04  is connected to the housing  02  in an electrically conductive manner via an electrically conductive seal  13 . The electrically conductive seal  13  may be realized as a textile seal or an elastomer seal. 
     The measuring system  01  additionally comprises a first measuring ring  14  having axial measuring surfaces, and a second measuring ring  15  having radial measuring surfaces. The measuring rings  14 ,  15  can be fixedly connected to the spindle. They are dimensioned in such a manner that they can be arranged within the carrier ring, and their measuring surfaces are sensed by the sensors  07 ,  08 , i.e. are positioned in the sensing range thereof. A first and a second measuring ring  14 ,  15  may be mechanically connected to each other in a fixed manner or, also, realized as a common component. 
     After the measuring system  01  has been attached to the spindle, relative displacements and tilting between the spindle and the spindle housing can be sensed in a contactless manner in all three spatial directions. 
     LIST OF REFERENCES 
       01  measuring system 
       02  housing 
       03  opening 
       04  connection cable 
       05  carrier ring 
       06  - 
       07  first sensors 
       08  second sensors 
       09  electronic modules 
       10  flexible printed circuit boards 
       11  - 
       12  encapsulation 
       13  conductive seal 
       14  first measuring ring 
       15  second measuring ring