Abstract:
A device for measuring forces generated by unbalance of a rotor, in particular a motor vehicle wheel, includes a stationary frame, an intermediate frame positioned radially within the stationary frame, and first levers supporting the intermediate frame on the stationary frame. The first levers are arranged along imaginary lines that are either parallel to each other or intersect at a first virtual mounting position. A pivot bearing is supported on the intermediate frame by second levers, which are arranged along imaginary lines that intersect at a second virtual mounting position. Mounted coaxially in the pivot bearing is a measuring shaft, which is rotatable about a common axis of the measuring shaft and the pivot bearing. An outer force sensor measures displacement between the intermediate frame and the stationary frame. An inner force sensor measures displacement between the pivot bearing and the intermediate frame.

Description:
This application is the national phase of international application PCT/EP99/06372 filed Aug. 30, 1999 which designated the United States. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a device for measuring forces that are generated by unbalance of a rotor. 
     2. Description of Related Art 
     A device for measuring forces that are generated by unbalance of a rotor is known, as shown by DE 33 32 978 A1. In such a device, it is known to mount the measuring shaft rotatably in two bearing units arranged at an axial distance from each other and supported via force sensors opposite a hollow bearing housing. This measuring shaft mounting is carried by a stationary frame. 
     From EP 0 343 265 A1 it is known, in the case of a balancing machine, to mount a backing girder—extending axially relative to the measuring shaft—in a pivotal manner with respect to a stationary frame. Sensors are arranged at an axial distance from each other, between the backing gird and the stationary frame. From DE 33 30 880 A1 it is known to support on a stationary frame a support—receiving the measuring shaft rotary mounting—via force transmitters arranged at an axial distance from each other 
     In a device known from EP 0 133 229 A1 used for balancing motor vehicle wheels, the measuring shaft is supported on a stationary frame in a mounting that has a force transmitter. To achieve a dynamic balancing, two mounting planes in which the force transmitters are also arranged are provided for the mounting of the measuring shaft. 
     From EP 0 058 860 B1 a balancing machine for rotary bodies is known in which the measuring shaft is mounted rotatably on an elastically flexible flat part arranged vertically on the machine bed. For this, the rotary mounting of the measuring shaft is provided at the upper edge of the flat part. Position excursions of the flat part are detected via an arm of sensors running at right angles to the flat part; the sensors&#39; force initiators run perpendicular to each other. In this connection, one of the sensors records the static portion while the other sensor detects the forces resulting from the dynamic unbalance and causing a twisting of the vertical, elastically flexible flat part around a center line, for example. 
     Furthermore, from DE-AS 16 98 164 an oscillation-measuring (supercritical) measuring system is known for mounting a rotor on leaf springs positioned diagonally to each other and whose extensions form a virtual intersection in one of the balancing planes of the rotor to be balanced. The two leaf springs positioned diagonally to each other are supported against a base plate via an intermediate plate on vertically standing leaf springs arranged parallel to each other. By means of oscillation transformers the vibrations of the leaf springs resulting from a rotor unbalance are detected and converted into corresponding measuring signals. 
     From DE-AS 10 27 427 and DE-AS 10 44 531 it is known, in the case of spring bars or plate springs that form oscillatory mountings in balancing machines, to form joints by thinning points. 
     The force sensors provided in known devices in the mounting planes at the measuring points supply sensor signals that are proportional to the centrifugal forces that result from the rotor unbalance and bring about the reaction forces measured by the sensors. With the conventional standard measuring systems for wheel balancing machines, a floating mounting is typical for the measuring shaft and the rotor clamped onto it. Translation onto the two balancing planes on the rotor for the dynamic balancing of the unbalance takes place based on the force lever law of statics. The forces measured in the two mounting planes by the sensors are thus independent of the respective distance of the rotor from the two sensors. Since these distances are different, a superproportional error in the balancing masses calculated for the respective balancing planes when the sensitivity of one of the two measuring converters is modified due to different influences, e.g. due to temperature, ageing, impact, overload, shaking in transport, humidity influence and the like. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to produce a device of the type mentioned in the beginning in which, due to the above-mentioned force dynamics a sensitivity modification of a measuring converter only slightly affects the mass balancing to be carried out in the balancing planes, e.g. by balancing weights to be attached. 
     In accordance with this invention, the above object is attained by a device in which a rigidly designed intermediate frame, on which a measuring shaft is supported in a mounting plane displaying a force sensor, is supported on a stationary frame via a further force sensor. The two force sensors are thus respectively situated in two mounting systems for a force-measuring unbalance detection, with each force sensor assigned to one of the two mounting systems. The two mounting systems are situated between the measuring shaft and the stationary frame, e.g., the balancing machine, on which the unbalance measurement is carried out on a motor vehicle wheel. In this connection, the force sensors may be situated in different mounting planes nevertheless situated in the area of the rigid intermediate frame, or in a common mounting plane. 
     With the design of the above-mentioned mounting systems, at least one more support is provided for the measuring shaft. The support has the property of a virtual mounting position in a further mounting plane. Two such mounting planes with such virtual mounting positions are provided for. The virtual mounting positions may be situated on both sides of the rotor to be measured. It is also possible, however, to provide for only one additional mounting plane having a virtual mounting position; this plane being situated preferably between the two balancing planes of the rotor or between the planes in which the force sensors are situated and the rotor. 
     The two force sensors are preferably arranged in a common mounting plane that runs perpendicular to the axis of the measuring shaft. The forces initiated in the force sensors as reaction forces are oriented parallel, particularly coaxially to each other and are situated in the common mounting plane. The force sensors may be situated in the area of the axial extension of the intermediate space in different mounting planes. 
     In a preferred embodiment, the measuring shaft is supported on the intermediate frame in a first mounting plane displaying a force sensor and in a second mounting plane displaying the virtual support point, and the intermediate fame in the one mounting plane is supported against the stationary frame via the second force sensor and, furthermore, is linked to the stationary frame by means of a parallel guide. The mounting plane displaying the dual support point can be situated between the rotor, particularly a motor vehicle wheel, and the mounting plane that has the two force sensors, or preferably between the two balancing planes of the rotor, particularly a motor vehicle wheel. 
     The intermediate frame can be supported via a pair of first support levers and joints at the respective ends of the first support levers. The measuring shaft can also be supported via a pair of second support levers and joints at the ends of the second support levers on the intermediate frame. The axes of the respective joints run perpendicular to the plane in which the forces introduced into the force sensors and the axis of the measuring shaft are situated. The pair of first support levers supporting the intermediate frame on the stationary frame can be provided in parallel to each other. For this, the first support levers run parallel to each other. It is also possible, however, to arrange the first support levers at an angle to each other, with the apex of the angle preferably situated in the axis of the measuring shaft or in the vicinity of this measuring shaft axis. The joints of the first support levers define the corners of a trapezoid. With this arrangement, the virtual mounting position situated on the outer side of the rotor is created. The virtual mounting position—support inside the rotor, particularly between the balancing planes—can also be formed by support levers arranged at an angle to each other and whose joints are supported in the corners of a horizontal trapezoid of the support lever arrangement. The support levers are preferably formed as rigid flat members, e.g., sheet metal parts, cast parts, rolled flat parts and the like which ensure along with the joints that the desired force e.g. running essentially linearly and axially, is introduced into the sensors. The support lever arrangement formed from the flat parts can be designed as a one-piece construction, wherein the flat parts are designed rigid and only the joints situated in between and running essentially linearly are flexible. The joints can be formed by weak points, e.g. constrictions between the individual flexible flat parts. In this way, flexible joint axes are formed between the flexible flat parts. With the corresponding arrangement, parallel or at an angle, the desired virtual mounting positions that are formed in the respective linearly extending mounting axes are then created, as explained above. 
     The virtual mounting positions are also the measuring points taken into account in the frame calculator of the balancing machine and representing vial measuring points. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     By means of the figures, embodiments of the invention are explained in greater detail. The following are shown: 
     FIG. 1 is a schematic of a first embodiment of the invention; 
     FIG. 2 is a schematic of a second embodiment of the invention; 
     FIG. 3 is a schematic of a third embodiment of the invention; 
     FIG. 4 is a schematic of a fourth embodiment of the invention; 
     FIG. 5 is a schematic of a fifth embodiment of the invention; 
     FIG. 6 is a schematic of a sixth embodiment of the invention; 
     FIG. 7 is a top view of a measuring arrangement and mounting for the measuring shaft, as may be used in the embodiments of FIGS. 1,  3  and  5 ; 
     FIG. 8 is a perspective view of the measuring arrangement of FIG. 7 seen from the front to the back; 
     FIG. 9 is a perspective illustration of the measuring arrangement of FIGS. 7 and 8 seen from above and from the side; and 
     FIG. 10 is a schematic of a seventh embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A rotor  1  is shown in a schematic diagram in the figures; the rotor  1  is attached for unbalance measuring to the measuring shaft  2  in known manner by clamping means (not illustrated in any further detail). The measuring shaft  2  is mounted rotatably on a stationary frame  6 , which can be the machine frame of a wheel balancing machine. A mounting  3  having force sensors  4 ,  5  is used to mount the measuring shaft  2 . The mounting  3  may include a tubular rotating bearing  26  in which the measuring shaft  2  is mounted rotatably. The rotary bearing  26  that receives the measuring shaft  2  is rigidly mounted in a first mounting plane  8  on an intermediate frame  7  over the inner sensor  4 . In addition, a virtual support point (also referred to herein as a virtual mounting position)  24  is established in another mounting plane  9  by second support levers  13 ,  14  that form a support lever pair and run at an angle to each other. The second support levers  13 ,  14  are arranged along imaginary lines or planes that intersect at the virtual support point  24 . The support point  24  acts like a swivel pin that runs perpendicular to the direction of force introduction of the reaction forces resulting from the unbalance measurement into the sensor  4 . The support levers  13  and  14  have ends connected flexibly (at joints  19  and  22 ) with the intermediate frame  7  and opposite ends connected flexibly (at joints  20 ,  21 ) with the rotating bearing  26 , which receives the measuring shaft  2 . The joint axes of the joints  19  through  22  run parallel to the swivel pin that is formed in the virtual mounting position  24 . As shown in FIGS. 1 and 2, the virtual mounting position  24  can be situated between the rotor  1  and the mounting plane  8  in which the force sensors  4  and  5  are situated. Alternatively, as shown in FIGS. 1 and 2, the virtual mounting position  24  may be situated in the area of the rotor between the balancing (compensating) planes  27 ,  28  in which the unbalance is balanced, for example, by attaching balancing weights. 
     The intermediate frame  7  is supported on the stationary frame  6  via the outer force sensor  5 . The force sensor  5  may be arranged in the mounting plane  8  situated perpendicular to the measuring shaft  2 . It is also possible, however, to arrange the force sensor  5  in another mounting plane, shifted in the axial direction of the measuring shaft  2 . Furthermore, the intermediate frame  7  is supported via a pair of support levers (i.e., first support levers  11  and  12 ) on the stationary frame  6 . The support levers  11 ,  12  have ends connected flexibly (at joints  15 ,  16 ) with the stationary frame  6 , and opposite ends connected flexibly (at joints  17 ,  18  in FIGS. 1,  3 ,  5 ,  10  and FIGS. 7 through 9 or joints  19 ,  22  in FIGS. 2,  4  and  6 ) with the intermediate frame  7 . The intermediate frame  7  is designed as a rigid mounting block or rigid, stiff mounting frame. 
     In the embodiments of FIGS. 1 and 2 as well as FIGS. 5 through 9, the support levers  11  and  12  run essentially parallel to each other and parallel to the axis  23  of the measuring shaft  2 . The support levers  11  and  12  thus form a parallel steering guide for the force introduction into the force sensor  5 —directed essentially perpendicular to the axis  23  of the measuring shaft  2 —of the reaction forces resulting during the unbalance measuring process. 
     In the embodiments of FIGS. 3,  4  and  10 , the two support levers  11  and  12  are arranged at a sharp angle to each other, the apex of which is situated in the axis  23  of the measuring shaft  2  or in the vicinity of the axis  23 . This apex forms a first virtual mounting position  25  in a mounting plane  10  situated on the outside of the rotor  1  and extending perpendicular to the measuring shaft  2 . 
     In the embodiment of FIG. 10 the first virtual mounting position  25  and the mounting plane  10  are situated in an extension, indicated as a dot-dash structure, of the measuring shaft  2  that runs—with respect to the mounting  3  of the measuring shaft  2 —opposite the longitudinal extension of the measuring shaft  2 . The first virtual mounting position  25  and the related mounting plane  10  are situated—with respect to the mounting  3 —on the side opposite the rotor  1  from the measuring shaft  2 . 
     The virtual mounting position  25  also has the property of a swivel pin that is situated perpendicular to the axis  23  of the measuring shaft  2  and perpendicular to the direction of introduction of the forces into the force sensors  4  and  5 . In the illustrated embodiments, this force introduction takes place in the mounting plane  8 . To form the swivel pin property in the respective virtual mounting positions  24  and  25 , the joint axes of the joints  15  through  22  run parallel to each other and perpendicular to the axis  23  of the measuring shaft  2  and to the force introduction direction of the reaction forces into the force sensors  4  and  5  in the mounting plane  8 . 
     In the embodiments of FIGS. 3 and 4, on opposite sides of the rotor  2 , namely on the inside and the outside of the rotor  2 , mounting planes  9  and  10  are respectively created with the virtual mounting positions  24  and  25 . The virtual mounting positions  24  and  25  have the properties of virtual measuring points. Forces L assigned to the inner mounting position  24  and forces R assigned to the outer mounting position  25  are introduced into the force sensor  4 . The force sensors  4  and  5  generate corresponding sensor signals L′ and R′. That virtual measuring points are also created in the virtual mounting positions  24  and  25  results from the fact that when a centrifugal force generated from the rotor unbalance engages the left mounting plane  9 , a measuring signal L′ proportional to the value of this centrifugal force is emitted by the force sensor  5 , while the force sensor  4  emits no signal. When the right outer mounting plane  10  is engaged by a centrifugal force R resulting from the rotor unbalance, only the force sensor  4  emits a proportional measuring signal R′, while the force sensor  5  generates no signal. This results in a floating mounting in which the balancing planes  27  and  28  are situated on the rotor  1  between the virtual measuring points/virtual measuring planes that concur with the mounting planes  9  and  10 , as shown in FIGS. 3 and 4. In the case of a force engagement—resulting from the rotor unbalance—between the mounting planes  9  and  10 , the mounting forces effective in these planes (virtual measuring planes) are divided up according to the mounting distances from the engagement point and corresponding sensor signals are emitted by the force sensors  4  and  5 . 
     In the embodiment shown in FIG. 10, the one virtual mounting position  24  at which a centrifugal force L resulting from the rotor unbalance can be effective is situated in the mounting plane  9  between the two balancing planes  27 ,  28 , preferably roughly in the middle between the two balancing planes  27 ,  28 . The other virtual mounting position  25  is situated with respect to the mounting  3  of the measuring shaft  2  on the other side in the extension of the measuring shaft  2 . Here a centrifugal force R resulting from the rotor unbalance is active. As already explained above, the sensors  4  and  5  deliver measuring signals R′ and L′ proportional to the centrifugal forces R and L. 
     In the embodiment of FIGS. 1 and 2 as well as FIGS. 5 through 9, the outer virtual mounting position is situated at infinity or at a relatively great distance of several meters, e.g., from roughly 3 to 20 m or more, because, due to parallel arrangement of the support levers  11  and  12 , essentially a parallel guide of the intermediate frame  7  is created. If a centrifugal force (L in FIGS. 1 and 2 and S in FIGS. 5 and 6) resulting from the rotor unbalance is introduced in these forms of construction in the mounting plane  9  (virtual measuring plane) at the virtual mounting position (virtual measuring point), this force is only detected by the force sensor  5  and a proportional signal L′/S′ is emitted by it. The force sensor  4  emits no signal. Regardless of the distance of the introduced centrifugal force, the force sensor  5  will only emit a signal proportional to the centrifugal force value due to the parallel guide of the intermediate frame  7 . The force sensor  4 , on the other hand, will emit a measuring signal M′ that is not only proportional to the centrifugal force value and thus to the unbalance value, but also to the distance of the force introduction point of the mounting plane  9 /the virtual mounting position  24 . 
     In the forms of construction of FIGS. 1,  3 ,  5  and  10  as well as FIGS. 7 through 9, the intermediate frame  7  is supported on the stationary frame  6  with the help of the support lever pair formed by the support levers  11  and  12 , and the tubular rotary mounting  26  of the measuring shaft  2  is supported by the support lever pair formed by the support levers  13  and  14 , one behind the other when observed in axial direction of the measuring shaft  2 . The support lever pairs of the embodiments of FIGS. 3 and 4 have the same direction of inclination. In the embodiment depicted in FIG. 10, the support lever pair  11 ,  12  has a direction of inclination that is opposite to the direction of inclination of the support lever pair  13 ,  14 . In the embodiments of FIGS. 2,  4  and  6 , the support frame  7  is supported on the stationary frame  6  and the rotary mounting  26  of the measuring shaft  2  is supported on the intermediate frame  7  with the respective support lever pair  11 ,  12  above (outside) support lever pair  13 ,  14 . The joints  17 ,  19  and  18 ,  22  can fall together as the common joints  19  and  22  on the intermediate frame  7 , as illustrated in FIGS. 2,  4  and  6 . 
     The support levers  11  through  14  can be formed by flat parts (or members) that are designed rigid and stiff. The flat parts can be formed of one piece, in connection with which the joints are formed by linear weak points, e.g. in the form of constrictions. As can be seen from FIGS. 7 through 9, the retaining device  29  comprises a retaining plate  33  that can be formed as a one-piece construction with the flat parts for the support levers  11  through  14 . The retaining plate  33  is fixedly connected with the tubular rotary mounting  26 , for example, by welding. In addition, an angle bracket  34  can also be provided as a component of the retaining device  29 . The angle bracket  34  is also fixedly connected with the retaining plate  3  and the rotary mounting  26 , for example by welding. In the figures, the upper angle bracket  34  is illustrated. A lower angle bracket can also be provided. The upper and lower angle brackets can also include an elbow, in which the rotary mounting  26  is connected fixedly and in guided manner through an opening in the elbow, e.g., by welding with the elbow. In this way, a rigid, stiff connection of the retaining device  29  with the rotary mounting  26  between the two joints  20  and  21  is created. The joints  20  and  21  are situated between the two support levers  13  and  14  and the retaining plate  33 . 
     From the one piece from which the flat parts for the support levers  11  through  14  are formed, attaching plates  37 ,  38  and  40 ,  41  can also be formed. The attaching plates  37 ,  38  are connected fixedly, for example by bolt connections or otherwise, with the stationary frame  6 . The attaching plates  37  and  38  form the attaching points for the support lever arm formed from the support levers  11  and  12  and with which the intermediate frame  7  is supported on the stationary frame  6 . Between the attaching plates  37  and  38  and the flat parts that form the support levers  11  and  12 , the joints  15  and  16  are formed by the linear weak points/constrictions. The weak points have a concave, particularly a semicircular cross-section. 
     In addition, the one-piece construction can include the two attaching plates  40  and  41  that are connected solidly, for example by bolt connections, welding or the like, with side surfaces of the intermediate frame  7 . Between the two attaching plates  40  and  41  and the support levers  11  and  12 , the joints  17  and  18  are formed by the weak points/constrictions. Between the flat parts that form the support levers  13  and  14 , the joints  19  and  22  are formed by weak points/constrictions. 
     In this way, from a single piece practically the entire mounting  3  is formed with which the measuring shaft  2  is supported on the stationary frame  6  and which predetermines the virtual mounting positions and measuring points. 
     The parallel guiding of the intermediate frame  7  on the stationary frame results essentially from the fact that the outlines of the concave constrictions  15 ,  17  and  16 ,  18  are situated on both sides of the support levers  11  and  12  roughly in parallel planes  35  and  36 , in which the guiding function of the two support levers  11  and  12  is achieved. The respective constrictions  15 ,  17  and  16 ,  18  are situated on opposite surfaces of the support levers  11  and  12  forming the flat parts. The support levers  11  and  12  are inclined toward each other at an extremely sharp angle, in connection with which, however, as already explained, the parallel steering guide is achieved by a guiding function in the parallel planes  35  and  36 . In this way, measuring arrangements corresponding to FIGS. 1 and 5 can be achieved. In order to achieve a measuring arrangement corresponding to FIG. 3, the support levers  11  and  12  can be inclined toward each other at a correspondingly wider angle. 
     In order to implement the embodiment illustrated in FIG. 10, the support levers  11 ,  12  in FIGS. 7 through 9 are oriented toward each other at their rear ends. The rear constrictions/joints  15 ,  16  are situated more closely to the axis of the measuring shaft  2  than the front constrictions/joints  17 ,  18 . 
     As FIG. 8 also shows, the two force sensors  4 ,  5  are arranged in a reference line, with the force sensor  4  arranged between the rotary mounting  6  and the inside of the intermediate frame  7  and the force sensor  5  between the outside of the intermediate frame  7 /the attaching plate  41  (FIG. 9) and the stationary frame  6 . 
     An electric motor  30  is provided for driving the measuring shaft  2  via a belt drive  31 . The motor  30  is mounted on the rotary mounting  26  via an extension arm. With this mounting, the measuring result is not affected by disturbances resulting from the motor drive. 
     Observed in axial direction, a compact mounting  3  for the measuring shaft  2  on the stationary frame  6  is created. This results—in connection with the reduced force dynamics, particularly with a floating mounting of the measuring shaft  2 —in a reduction of the influence of changes in sensitivity of the force recorders, for example, as a result of different effects of temperature, ageing, impact, overloading, shaking during transport and humidity, a reduced need to replace the force sensors, for readjustments of the measuring arrangement after transport and setup of the machine, reduced service costs, improved measuring precision, reduced demands on the resolution of the AD-converters during digitalization of the analog measuring signals and a greater virtual distance of the measuring planes in spite of the compact construction. Despite the stationary mounting of the measuring shaft, reduced force dynamics are achieved similar to those of a measuring arrangement with two mounting positions on both sides of the rotor.