Abstract:
Torque transmitted via a drive shaft of a motor is contactlessly determined using organic magnetoresistive semiconductor element, unlike known torque sensors that can generate greatly fluctuating measurement signals even at a constant torque. The organic magnetoresistive semiconductor element is mounted on a drive shaft or a coupling thereof. For this purpose, a field generator is provided, which is rigidly connected to the drive shaft or the clutch and which in the environment of the drive shaft generates a magnetic field that is dependent upon the torque. In the environment, the OMR semiconductor element is arranged to be stationary. The OMR semiconductor element has two electrodes between which a voltage source generates an electrical voltage.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. national stage of International Application No. PCT/EP2011/064227, filed Aug. 18, 2011 and claims the benefit thereof. The international application is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    Described below is a device for determining a torque which acts on a drive shaft. The drive shaft can be, for example, a shaft between a motor and a working machine, via which a torque from the motor is transmitted to the drive machine. Also described is a method for determining the torque. 
         [0003]    The registration of a torque on a shaft or on a coupling for such a shaft is applied in industrial drive technology, in power technology, in web drives and in automobile technology. In one embodiment of torque sensors, the determination of the torque is carried out without contact. Here, a signal correlated with a direction or magnitude of the torque is transferred from the rotating parts (shaft or coupling) to a fixed sensor, for example via an air gap. Thus, no wearing parts, such as wiping contacts, for example, have to be used. This considerably increases the reliability of the sensors. 
         [0004]    A signal correlated with the transmitted torque can be generated by a magnetic device which is fixed to the shaft and which generates a magnetic field. This magnetic field is measured by a magnetic field sensor arranged in a stationary manner in the vicinity of the shaft and is processed further by suitable electronics. The magnetic field sensors used are Hall sensors or sensors which are based on the AMR effect (anisotropic magnetoresistive effect). The disadvantage with a magnetic field-based torque sensor is that the magnetic field sensors used generate highly fluctuating signals even in the case of a constant torque. Therefore, a relatively high expenditure on switching is necessary in order to determine a torque with a magnetic field-based torque sensor reliably. 
       SUMMARY 
       [0005]    Described below is a device used to determine a torque on a drive shaft or on a coupling of the same. 
         [0006]    In the device, use is made of an organic magnetoresistive semiconductor element (OMR semiconductor element), in order to determine the torque on a drive shaft or on the coupling without contact. An OMR semiconductor element is based on an organic semiconductor and changes its electrical resistance as a function of a magnetic field when the latter penetrates the OMR semiconductor element. 
         [0007]    In order to register the torque, the device has a field generating device which is firmly connected to the drive shaft or a coupling of the same and which, in the surroundings of the drive shaft, generates a magnetic field that depends on the torque (the direction and/or magnitude of the latter). In the surroundings in which the field is generated, the OMR semiconductor element is arranged in a stationary manner. The OMR semiconductor element has two electrodes, between which a voltage source of the device generates an electric current or an electric voltage. 
         [0008]    By using the device, the torque can be determined in the following way in accordance with the method. Using the field generating device, a magnetic field is generated on the drive shaft (or possibly on the coupling) as a function of the torque. 
         [0009]    This field is detected in the surroundings of the drive shaft by the OMR semiconductor element. This makes it possible, by the OMR semiconductor element, to set an electric variable as a function of the detected magnetic field. This electric variable can be, for example, a current flowing between the electrodes. A constant-current or constant-voltage measurement may be made possible by the voltage source. 
         [0010]    The device and the method have the advantage that a measured signal determined thereby for the torque exhibits only relatively small fluctuations, which are not caused by a torque change. In addition, on the basis thereof, it is possible to produce a torque sensor with little effort and low costs. 
         [0011]    The OMR semiconductor element can be formed as a layer which surrounds the drive shaft and/or the coupling, at least in some regions. In this way, by the OMR semiconductor element, as compared with detection using a Hall sensor or an AMR sensor, the magnetic field is not detected in point form, so to speak, but relatively over a large area. During the measurement of the torque, this results in averaging effects, which ensure a low-fluctuation measured signal. An embodiment of the device has an OMR semiconductor element which has the shape of a hollow cylinder. This hollow-cylindrical OMR semiconductor element surrounds the drive shaft in the circumferential direction of the drive shaft, so that fluctuation of the measured signal, such as could be caused by a rotation of the drive shaft, is effectively suppressed. An OMR semiconductor element in the shape of a segment of a hollow cylinder can prove to be likewise beneficial, since the element can be removed from the surroundings of the drive shaft with little effort (for example for repair purposes). In addition, it is also possible to form it, for example, as a shaft protector. 
         [0012]    A further advantage results if the OMR semiconductor element is arranged on a flexible substrate. This allows a very simple, space-saving structure of a housing of the device and permits simple, economical mounting of the torque sensor system. 
         [0013]    Another development of the device provides a measuring device for measuring a variable which is proportional to a current flowing through the OMR semiconductor element and/or to a voltage present on the OMR semiconductor element. This variable can be, for example, the current or the voltage itself or an electric voltage which is dropped across a further element through which the same current flows as through the OMR semiconductor element. On the basis of a measured signal for the variable, automated monitoring of the torque can advantageously be provided or a control signal for an indicator can be formed. 
         [0014]    A particularly good measuring effect for the torque results if the OMR semiconductor element is operated with a constant voltage within an operating range in which the OMR semiconductor element exhibits a maximum field sensitivity. Accordingly, an advantageous development of the device provides for the voltage source to be designed as a constant-voltage source. The field sensitivity in this case indicates the change dR in the electrical resistance of the OMR semiconductor element relative to a change in the magnetic field strength dH, i.e. dR/dH. 
         [0015]    According to another advantageous development of the device, an OLED, which means an organic light-emitting diode, is formed by the OMR semiconductor element. This can be achieved by an appropriate selection of the organic semiconductor material used for the production of the OMR semiconductor element. By an OLED, in a manner that can be implemented simply, a visual display of the torque transmitted by the shaft is made possible. For example, it is possible to achieve the situation where a region of the shaft in which a high torque acts appears to be brighter than a less loaded region. 
         [0016]    Another advantageous type of optical torque indication is provided if the electric voltage which is generated between the electrodes of the OLED is set to a value at which the OLED only illuminates if the torque satisfies a predetermined criterion. Thus, by appropriate pre-definition of the criterion, it is possible for example to indicate whether a specific minimum torque is being transmitted or whether a maximum permissible torque is being exceeded, for instance. 
         [0017]    In another advantageous development of the device, the device has at least two OMR semiconductor elements which are each configured in one of the ways already described. In this development, the OMR semiconductor elements can have different characteristic curves, so that they exhibit different magnetoresistive properties. Additionally or alternatively, electric voltages of different magnitudes are generated between the respective electrodes of the OMR semiconductor elements during operation of the device. Providing a plurality of OMR semiconductor elements results in the advantage that the maximum field sensitivity in each OMR semiconductor element can be provided for a different absolute magnetic field strength. This enables accurate measurement of the torque over a greater torque range. 
         [0018]    In conjunction with the provision of a plurality of OMR semiconductor elements, which each also form an OLED, a further advantage results if the OLEDs have different illumination limits in relation to the torque. In this case, an illumination limit is to be understood to mean that magnetic field strength at which, when exceeded, the respective OLED illuminates. By such an arrangement, limits for torque ranges can be predefined. In relation to the individual torque ranges, the correspondingly illuminating OLEDs then indicate in which of the ranges a current torque currently lies. Using an appropriately high number of OLEDs, it is even possible for a virtually continuous visual indication of the torque on the drive shaft or the coupling to be provided. 
         [0019]    In conjunction with generating the magnetic field on the drive shaft or coupling, an embodiment of the device provides for the field generating device to have two magnetic elements, of which the relative position to each other depends on the torque. In this case, it is conceivable for a magnet, as a first magnetic element, to be covered by a second, soft-magnetic element, which shields the magnet with respect to the surroundings of the drive shaft. By an appropriate mechanism, the soft-magnetic element can then be displaced as a function of the torque, so that part of the field from the magnet reaches the surroundings. 
         [0020]    In an embodiment of the device, the field generating device includes an element which generates the magnetic field by inverse magnetostriction as a function of a change in its shape which is caused by the torque. This embodiment has the advantage that no mechanical arrangement that is susceptible to faults is needed to generate a variable magnetic field. 
         [0021]    Also described below are developments of the device and the method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
           [0023]      FIG. 1  is a schematic, partially perspective, illustration of a torque sensor according to one embodiment of the device, 
           [0024]      FIG. 2  is graph of a basic course of characteristic curves of an OMR sensor and an OLED, respectively, and 
           [0025]      FIG. 3  is a schematic, partially perspective, illustration of a torque sensor according to a further embodiment of the device. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
         [0027]      FIG. 1  shows a motor  10  and a working machine  12 . The working machine  12  can be, for example, a milling machine or a conveyor belt. The working machine  12  is driven by the motor  10 . For this purpose, the motor  10  is coupled to the working machine  12  via a shaft  14 , via which the motor  10  transmits a motor torque  16  to a coupling (not specifically illustrated) of the working machine  12 . The shaft  14  rotates about its longitudinal axis. At the coupling, a load torque  18  from the working machine  12  acts on the shaft  14 . 
         [0028]    During an operation of the working machine  12 , it is intended to determine how high the torque transmitted from the motor  10  via the shaft  14  to the working machine  12  is. For this purpose, a torsional force acting on the shaft  14  is measured by using a torque sensor  20  on the shaft  14 . The torsional force results from the motor torque  16  and the load torque  18  acting against the latter. From the torsional force determined, it is possible to draw conclusions about the torque transmitted. 
         [0029]    The torque sensor  20  is one embodiment of the device. The measurement is carried out without contact. For this purpose, the shaft  14  is arranged concentrically in a sleeve  22 . The sleeve  22  does not touch the shaft  14 , so that the shaft  14  can rotate in the sleeve  22 . The sleeve  22  is firmly connected to a base (not illustrated) and does not co-rotate with the shaft  14 . 
         [0030]    The sleeve  22  has a layer  22 ′ of an organic semiconductor material, in which an electrical resistance depends on a field strength of a magnetic field penetrating the semiconductor material (magnetoresistive effect). The magnetic field is generated by a magnetic coating, which is a constituent part of the shaft  14  and which, during operation of the sleeve  22 , is located on or in a steel rod of the shaft  14 . The coating is firmly connected to the rod such that the shape thereof changes together with that of the rod when the torsional force to be measured acts on the latter. The magnetic coating includes a magnetic material which generates a magnetic stray field around the shaft  14  or at the ends of the coating, the field strength of the field depending on the shape of a body formed by the coating (inverse magnetostriction). This magnetic field penetrates the sleeve  22 . A field strength of the magnetic field is greater, the greater the torsional force that acts on the shaft  14 . 
         [0031]    By using  FIG. 1  and  FIG. 2 , the following text explains how the torque transmitted via the shaft  14 , i.e. the torsional force acting on the shaft  14 , is determined. 
         [0032]    The layer  22 ′ of the organic semiconductor material located on the sleeve  22  is connected electrically to a voltage source  28  via two electrodes  24 ,  26 . The voltage source  28  generates an electric voltage U having the voltage value U0 between the electrodes  24 ,  26 . For the case in which no torsional force acts on the shaft  14 , an electric current I having the current intensity I0 flows through the layer  22 ′ as a result. This corresponds to a working point A on a U/I characteristic curve K 1  of the organic semiconductor material. A characteristic curve K 2  results if the organic semiconductor material is penetrated by a magnetic field having a specific, higher field strength. In this way, for the case in which the voltage source  28  generates a constant voltage U with the voltage value U0, the current I rises by a current intensity value dI. If, on the other hand, a constant current I with the current intensity I0 is generated by the voltage source  28 , then the voltage U decreases by a voltage value dU. 
         [0033]    If the voltage source  28  used is a constant-voltage source, it is possible, for the quantitative measurement of the magnetic field, to obtain a current increase dI of about ten to thirty per cent relative to I0 by the arrangement shown in  FIG. 1 . This permits a very accurate measurement of the change in the magnetic field strength. 
         [0034]    Using a measuring circuit  30 , a voltage Um on the layer  22 ′ is measured between two measuring electrodes  32 ,  34  of the measuring circuit  30 . The voltage Um is caused by the current I. The measured voltage Um is amplified electronically by an amplifier  36  of the measuring circuit  30 . The signal amplified in this way is transmitted to an indicating device  38  of the measuring circuit  30  which, on the basis of the signal, determines and indicates the torsional force acting on the shaft  14  and therefore the torque transmitted via the shaft  14 . The values of the voltage Um and therefore also the amplified signal exhibit only slight fluctuations in the case of a constant torque. Since the sleeve  22  and therefore also the layer  22 ′ surround the shaft  14  completely in the circumferential direction, any asymmetry of the magnetic field which, because of the rotation of the shaft  14 , generates a periodically fluctuating field strength in each point of the sleeve  22 , does not act on the voltage Um, as a result of an averaging effect in the layer  22 ′. In the case of a Hall sensor, which cannot be configured so flatly as the organic semiconductor element and which therefore detects the magnetic field only at a point, the rotation of the shaft  14  would cause a fluctuating signal. 
         [0035]    The current I and the voltage Um are electric variables which are varied as a function of the magnetic field by the magnetoresistive effect of the layer  22 ′. 
         [0036]    Instead of the voltage Um, a measured current can also be measured by the measuring circuit  30 . 
         [0037]    The organic semiconductor material of the layer  22 ′ represents an OLED which illuminates when the current intensity of the current I flowing through the same exceeds a specific current intensity value. The voltage U of the voltage source  28  is set in such a way that the illuminating effect begins when the torque acting on the shaft  14  is greater than a maximum permissible torque. In this way, an operator of the working machine  12  is then shown immediately by luminescent regions  40  of the layer  22 ′ that the motor  12 , the working machine  12  or the shaft  14  is overloaded. 
         [0038]    To form the layer  22 ′, the organic semiconductor material has been applied to a flexible substrate. This can be, for example, polyethylene (PET) or a polyimide, such as can be obtained, for example, under the description Kapton. 
         [0039]      FIG. 3  shows a further arrangement with a motor  10 , a working machine  12  and a shaft  14 . In  FIG. 3 , elements which, in their function, correspond to elements shown in  FIG. 1 , are provided with the same designations as in  FIG. 1 . 
         [0040]    In the example shown in  FIG. 3 , a torque sensor  42  has three rings  44 ,  46 ,  48 , each of which has a layer of an organic semiconductor material, by which an OLED is formed. The torque sensor  42  is an embodiment of the device. In each of the three layers there flows a current which is generated by a voltage source (not illustrated) in a similar way to that which has already been explained in conjunction with  FIG. 1 . The three rings  44 ,  46 ,  48  are penetrated by a magnetic field, which is generated by the shaft  14  in the manner already described. 
         [0041]    Each of the rings  44 ,  46 ,  48  has a different illumination limit: if, via the shaft  14 , a torque is transmitted which is greater than a predetermined minimum torque, then the ring  48  illuminates, while the other rings  44 ,  46  initially remain dark. Only when the torque exceeds a lower limit of a normal or else working torque range does the ring  46  also illuminate. If a predetermined maximum permissible or else overload torque is exceeded, the ring  44  also illuminates. If the overload torque is exceeded repeatedly and only briefly as a result of step changes in load, then the ring  44  flashes. Through this signaling, dynamic load peaks can be detected by an operator. 
         [0042]    The torque sensors described can also be arranged on a coupling instead of a shaft. Furthermore, they can be used to determine a torque which is transmitted via a shaft to a generator. 
         [0043]    The examples show how, by the flat and continuous coating of a sleeve or of a ring, each of which can be made of a flexible material, a structurally advantageous measurement of the torque is made possible. In addition, the torques on the shaft can be visualized by the illuminating effect. 
         [0044]    A description has been provided with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).