Abstract:
The invention relates to a torque sensor comprising an inner body, an outer annular body surrounding the inner body concentrically and webs connecting the inner body to the outer annular body in a star shape. Further on the torque sensor comprises a means for introducing torque and at least one measuring element on a web for determining deformation. The webs have the form of a u-profile.

Description:
FIELD OF THE INVENTION 
     The invention generally relates to sensors and in particular it relates to torque sensors. 
     BACKGROUND OF THE INVENTION 
     Torque sensors are sensors that determine torque by deformation of a measuring body. Most torque sensors operate with strain gauges. There are also torque sensors, which operate on the piezoelectric, the magneto-elastic or the optical principle. 
     Torque sensors are used on rotating or stationary shafts for the determination of the transmitted torque, but also in calibrating devices for torque wrenches. For short build and very stiff tools to be calibrated, such as torque wrenches, often so-called torque measurement flanges are used. The torque measurement flanges as generic torque sensors consist of an inner hub that is connected by several spokes to an outer ring. The spokes wear sensors, such as strain gauges that measure the bending load at an applied torque. In such torque sensors the influence of lateral forces and lateral moments should be compensated as far as possible. Moreover, the torque sensor should be characterized by low mass moment of inertia and high measuring sensitivity. 
     With a torque sensor according to the German patent DE 42 08 522 C2 not bending forces, but shear forces are measured. To this end the torque sensor has an inner body or inner hub and a concentric outer annular body. The inner body is connected to the outer annular body by webs extending in star shape. The measuring sensors, for example strain gauges are seated on the webs for the detection of torsion. 
     In the German patent application DE 195 25 231 A1 a torque sensor is described, which consists of two opposing flanges that are interconnected by webs. Strain gauges are provided on the connecting webs. The cost of this variant of torque sensors are also relatively high. In addition, the dynamic behavior of such torque sensors is very inadequate. A further disadvantage of the torque sensor described therein is, that a shift of the zero point still occurs at high rotation speeds, and that the manufacturing costs of such torque sensors are extremely high. 
     DE 202 09 850 U1 discloses a torque sensor with webs and having an inner body and an outer annular body concentrically surrounding the inner body. Webs with different widths connect the inner body with the annular body in a star shape. Measuring elements, which are provided on the webs, determine the torsion of the webs generated by an applied torque. 
     A disadvantage of the aforementioned torque sensors is that the manufacturing cost of the torque sensors is correlated with their accuracy. 
     Thus, it has been long felt and unsolved need to create a torque sensor, which eliminates the disadvantages of the above-mentioned state of the art and is designed as cost-effective and simple as possible and yet sensitive and accurate. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a torque sensor comprising an inner body, an outer annular body surrounding the inner body concentrically, webs connecting the inner body to the outer annular body in a star shape, means for introducing torque, and at least one measuring element on a web for determining deformation, wherein the webs have the form of a u-profile. 
     In one embodiment of the invention the u-profiles have the ratio of width of the u-profile to height of the u-profile from 1 to 1.5. With this ratio, a high bending rigidity and low impact of lateral forces on the measuring elements is achieved. 
     As to another aspect of the invention it is advantageous to arrange the u-profiles in the ratio of torque sensor radius to web center radius from 1.5 to 2.5 relative to the center of the torque sensor. This avoids torque peaks and distributes the introduced force homogeneous. 
     As to another aspect of the invention, u-profiles are provided having different thickness in height and/or width. This allows more variability in statics and weight distribution of the webs, so an improved measurement result of the torque senor is achieved. 
     As to still another aspect of the invention, the measuring elements are respectively arranged at the u-profiles. By this measure, the torsion or deformation can be measured particularly well when torque is applied, to the torque sensor. 
     As to a still further aspect of the invention the torque sensor comprises a polygon socket. The polygon socket form-fittingly receives an outer polygon of a torque wrench during the measurement. 
     As to still another aspect of the present invention, the measuring element is a strain gauge. By the strain gauge the deformation is particularly easy detectable. 
     Further modifications, advantages and features of the present invention become apparent from the subject matter of the claims, as well as the drawings with the corresponding description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention will be now described in greater detail herein below with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic front view of a torque sensor according to the invention. 
         FIG. 2  is a schematic cross section view through the torque sensor. 
         FIG. 3  is a schematic three-dimensional view of the front of the torque sensor. 
         FIG. 4  is a schematic three-dimensional view of the rear of the torque sensor. 
         FIG. 5  is a schematic cross-section view of a u-profile. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is based on the principle that lateral forces and torque forces, which are applied to the torque sensor by the force introduction, are optimally distributed to the webs with the measuring elements for detecting deformation. It is essential that the u-profile has a very high resistance to lateral forces, so that the webs obtain a local stability and the effects of lateral forces are radically minimized during the measurement. In this manner, the number of webs can be reduced, because each web on its own is formed considerably more stable. 
     In one embodiment of the invention the torque sensor is provided in the form of a polygon socket. The polygon socket form-fittingly receives an outer polygon of a torque wrench during the measurement. 
     The polygon socket comprises a cut-out on its surfaces, which receives, for example, a spring-loaded ball of an outer polygon of a torque wrench. The cut-out effectuates a free centering of the outer polygon in the polygon socket. In this way measuring errors, which result from centering errors, are significantly reduced, because lateral forces are extensively eliminated. 
     To improve the dynamic behavior the masses of the inner body and the outer body are different. This is achieved, for example, by the inner body and the outer annular body having different volumes or different density. Due to the different moments of inertia, which are present because of the different densities, additional adjustable parameters are obtained for improving the accuracy of the torque sensor. In a suitable embodiment, the outer annular body has a larger mass than the inner body. This is particularly advantageous when the inner body and the outer annular body have different densities, particularly when the outer annular body has a greater density than the inner body. Thus, the torque sensor obtains a different moment of inertia in the inner body than in the outer annular body, which leads to an improvement of the dynamic behavior of the torque sensor. 
     It is advantageous to provide a torque sensor with a plurality of u-profiles in general, and with two to four u-profiles in particular. By the number of webs the ratio of stiffness and elastic deformation can be influenced and the torque sensor can be excellently adapted to different use cases. Normally, the influence of lateral forces increases when reducing the number of webs. 
     The effect of lateral forces is compensated by the u-profiles, which have a particularly high resistance to such forces, so that the number of webs can be reduced while maintaining the accuracy during the measurement process. Moreover, by reducing the webs to two u-profiles, a lower-cost production of the torque sensor is achieved. 
     Referring now to the drawings in general, and to  FIG. 1  in particular, which shows a front view of a torque sensor  10 . The torque sensor  10  comprises an inner body  12  which is surrounded by an outer annular body  14 . The inner body  12  is connected to the outer ring body  14  by radial extending webs  16 . The webs  16  are formed u-shaped as u-profiles  17 . The webs  16  connect the inner body  12  to the outer annular body  14 , wherein in this exemplary embodiment the intermediate space  18  has the shape of a ring segment with rounded end regions. 
     In the center of the inner body  12  of the torque sensor  10 , a pin  20  is visible, which is provided with a countersink  22  and a recess  24 . In this exemplary embodiment, the recess  24  is formed as a square socket. Further on, a cut-out  26  is located on the surfaces of the square socket in form of a semi-circular cutout to receive, for example, a spring-loaded ball or pin of the external square of a torque wrench. Usually the torque wrench has a spring-loaded ball or pin on its external square, which moves in when receiving a tool and is pressed against the square socket of the insert during the engagement. This leads to a connection of torque wrench and insert or torque sensor and ensures optimum force introduction during the measurement process. 
     Other through holes  28  in the outer annular body  14  have a structural and weight reducing function or can be screwed to according shaft flanges, in order to transfer torque. 
     At the u-profiles  17  measuring elements  32  are provided for detecting the deformation of the webs  16 . Preferably, these measuring elements  32  are strain gauges, which provide an electrical signal corresponding to the deformation to an evaluation device, not shown. By appropriately applying a torque to the torque sensor  10 , the forces are optimally distributed to the webs  16 . To this end, the u-profile  17  eliminates lateral forces caused by clamping and twisting of the torque wrench, which can occur when the torque is introduced. These forces are compensated directly at the measuring element by the legs of the u-profile  17 . 
     Preferably, a strain gauge with two measuring grids is attached to each u-profile  17 , wherein the grid angle is 45° relative to the longitudinal axis of the web. (The strain gauges are shown schematically.) A very high output signal is obtained when the measuring elements are connected into a Wheatstone measuring bridge. If the torque sensor  10  is subject to an applied torque a shear load in circumferential direction can be determined with high sensitivity by the arrangement of the strain gauges. 
     The inner body  12  has a smaller mass than the outer annular body  14 . This is, for example, created by materials of different density. 
       FIG. 1  also illustrates the different ratios R/r of torque sensor radius  19  to web center radius  21 . For additional stability optimization of the torque sensor, the ratio is 1.5 to 2.5. 
       FIG. 2  shows a schematic cross section through the torque sensor  10 . The section plane is located in the region of the webs  16 . The figure shows the relatively simple assembling of the torque sensor  10 , which comprises the outer annular body  14  and the inner body  12 . The measuring elements  32  are located on the u-profiles  17  of the webs  16 . In doing so, a cost-effective production of the torque sensor  10  is given, since complex milling or drilling is not necessary. Furthermore, the pin  20 , the countersink  22 , the recess  24  and the cut-out  26  for receiving the spring-loaded ball of the torque wrench are visible. The height  36  and width  38  ( FIG. 5 ) of the u-profiles are shown in  FIG. 2 . 
     From the perspective view of the torque sensor  10  in  FIG. 3  (front view) and  FIG. 4  (rear view) more details are visible. The contours of the u-profiles  17  are particularly well visible on the rear side ( FIG. 4 ) of the torque sensor  10 . In contrast, the measuring elements  32  are arranged on the front side of the torque sensor  10 . 
     The three-dimensional view further shows that the intermediate spaces  18  which have the shape of a ring segment with rounded end regions are continuous. In this way, in particular a weight reduction of the inner body  12  is possible. It is shown in at least  FIGS. 3 and 4  that each intermediate space  18  is formed as a narrow circumferential slot extending along the outer circumferential periphery of the inner body. The narrow circumferential slots are separated from a central socket by a substantial uninterrupted area of the inner body. 
     The three-dimensional view further shows that the intermediate spaces  18  which have the shape of a ring segment with rounded end regions are continuous. In this way, in particular a weight reduction of the inner body  12  is possible. 
       FIG. 5  shows a cross section through the u-profile  17 . The u-profile  17  has different thicknesses at its height  36  and/or width  38 . In doing so, a notable stability, flexural strength and shear strength of the webs  16  is assured, because the width of the u-profile  17 , i.e. the extension in the circumferential direction, and the height, i.e. the extension in the axial direction, is provided in the ratio b/h from 1 to 1.5. This induces an additional variability in statics and weight distribution of the torque sensor.