Abstract:
A gear mechanism includes a rotating input element, a rotating output element, and at least one first force transmission device arranged along a spiral line on a face of the input element. A second force transmission device is arranged along an encircling line on a face of the output element. The interaction of these force transmission devices transmits a turning moment from the input element to the output element, whereby this turning moment effects a rotating motion in the output element so that the rotational speed is lower than the rotational speed of the input element. A rotary encoder may be equipped with a gear mechanism of the aforementioned type.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a gearing and to a rotary encoder equipped with such gearing. 
   BACKGROUND INFORMATION 
   In addition to angle-measuring instruments, which allow an angle measurement at a rotatable shaft in incrementable measuring steps, so-called absolute angle-measuring instruments—also referred to as rotary encoders—are conventional as well. These allow an absolute angle determination within a single shaft rotation. Furthermore, if the number of performed shaft rotations is to be recorded as well, so-called multiturn rotary encoders are generally utilized. With such multiturn rotary encoders, the absolute angular position is determined within one shaft rotation, i.e., between 0° and 360°, via a code disk connected to the shaft, which is scanned with the aid of a suitable photoelectric scanning unit. To obtain the required information regarding the number of effected shaft rotations, a reduction or step-down gear is typically provided, via which one or more additional graduated disks or code disks is/are set into a rotary motion having a low number of revolutions per unit of time, while the shaft is rotating. These code disks are often designed as magnetized disks, each having at least one north-pole and one south-pole sector. The rotational position of these additional code disks is normally recorded in a conventional manner with the aid of suitable scanning units, in particular Hall sensors. Due to the specified reduction of the rotary motion of the additional code disks, it is possible to ascertain the number of effected rotations of the shaft in this manner. A measurement of the absolute position of the driven shaft may thus be carried out also over a plurality of rotations. 
   It may be advantageous in such reduction gearings if the first reduction step utilizes the highest possible reduction ratio so that the gear wheels of the subsequent gearing steps rotate at an already considerably lower rotational frequency. This significantly reduces the loading of the subsequent gear steps. 
   A similarly configured multiturn rotary encoder is described in German Published Patent Application No. 198 20 014, of the applicant hereof. This describes an integrated construction method for electronic components of rotary encoders. 
   German Published Patent Application No. 197 45 177 describes a gearing system in which permanently magnetic or ferromagnetic, spiral-shaped segments are arranged along the peripheral areas of a drive gear and an output gear. This design may be disadvantageous insofar as it requires relatively large installation space, in particular as far as the outer dimensions in the radial direction are concerned. 
   The demand for rotary encoders having smaller structural dimensions continues to grow. Since the electronic components of rotary encoders are integrated to an ever greater extent and are thus miniaturized as well, the installation space for the mechanical components of these devices often becomes a limiting factor in such miniaturization endeavors. 
   SUMMARY 
   An example embodiment of the present invention may provide a gearing that has small structural dimensions and may be produced at low cost. 
   The gearing may be used in a rotary encoder. 
   In an example embodiment of the present invention, a very high reduction ratio may be achieved by the gearing, and the outer diameter of the entire rotary encoder may be kept small at the same time. Furthermore, the installation space required in the axial direction may be comparatively low. In addition, the gearing according to an example embodiment of the present invention may have a relatively low mass inertia, which may be advantageous especially with high dynamic changes in rotary motions. 
   In the following text, the end face of the drive or output element should be understood as an area that is substantially perpendicular to its axis of rotation. In a circular-cylindrical drive or output element, the end face should thus not be understood as the lateral surface but as one of the circular or ring surfaces. 
   The force-transmission arrangement of the gearing may be configured as permanent magnets. The permanent magnets are arranged on the drive gear along a spiral line and the permanent magnets on the output element are arranged along a circular curve, for instance. The action of the gearing may be improved if the spiral line on the drive element is configured as part of an Archimedean spiral. To increase the magnetic forces, the bodies of the drive gear and the output gear to which the permanent magnets are affixed may be made of a material having high relative permeability, which, as a minimum, exceeds the value 10 and is greater than 100, for example. 
   According to an example embodiment of the present invention, a gearing includes: a rotatable drive element; a rotatable output element; at least one first force-transmission device arranged at an end face of the drive element along at least one spiral line; and a second force-transmission device arranged at an end face of the output element along a circumferential line. In accordance with reciprocal action of the first force-transmission device and the second force-transmission device, the first force-transmission device and the second force-transmission device are configured to transmit torque from the drive element to the output element to effect a rotary motion in the output element. A frequency of rotation of the output element is lower than a frequency of rotation of the drive element. 
   According to an example embodiment of the present invention, a rotary encoder includes at least one gear step. Each gear step includes: a rotatable drive element; a rotatable output element; at least one first force-transmission device arranged at an end face of the drive element along at least one spiral line; and a second force-transmission device arranged at an end face of the output element along a circumferential line. In accordance with reciprocal action of the first force-transmission device and the second force-transmission device, the first transmission device and the second transmission device are configured to transmit torque from the drive element to the output element to effect a rotary motion in the output element, and a frequency of rotation of the output element is lower than a frequency of rotation of the drive element. 
   According to an example embodiment of the present invention, a gearing includes: rotatable drive means; rotatable output means; at least one first force-transmission means arranged at an end face of the drive means along at least one spiral line; and second force-transmission means arranged at an end face of the output means along a circumferential line. In accordance with reciprocal action of the first force-transmission means and the second force-transmission means, the first force-transmission means and the second force-transmission means transmit torque from the drive means to the output means to effect a rotary motion in the output means, and a frequency of rotation of the output means is lower than a frequency of rotation of the drive means. 
   According to an example embodiment of the present invention, a rotary encoder includes at least one gear step. Each gear step includes: a rotatable drive means; a rotatable output means; at least one first force-transmission means arranged at an end face of the drive means along at least one spiral line; and a second force-transmission means arranged at an end face of the output means along a circumferential line. In accordance with reciprocal action of the first force-transmission means and the second force-transmission means, the first force-transmission means and the second force-transmission means transmit torque from the drive means to the output means to effect a rotary motion in the output means, and a frequency of rotation of the output means is lower than a frequency of rotation of the drive means. 
   Further details and aspects of the gearing and a rotary encoder provided therewith are set forth in the following description of exemplary embodiments with reference to the appended Figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1   a  is a plan view of the drive gear having permanent magnets. 
       FIG. 1   b  is a side view with a partial section of the drive gear having permanent magnets. 
       FIG. 1   c  is a perspective view of the drive gear. 
       FIG. 2   a  is a plan view of the output gear with permanent magnets and driving pins. 
       FIG. 2   b  is a side view including a partial section of the output gear with permanent magnets and driving pins. 
       FIG. 2   c  is a perspective view of the output gear with permanent magnets and driving pins. 
       FIG. 2   d  is a plan view of the output gear with driving pins arranged inside the permanent magnets. 
       FIG. 2   e  is a side view including a partial section of the output gear with driving pins arranged inside the permanent magnets. 
       FIG. 3   a  is a side view of the drive gear and the output gear in the operating position. 
       FIG. 3   b  is a perspective view of the gearing with permanent magnets and tilted output axle as well as driving pins. 
       FIG. 3   c  a side view with a partial section of the drive gear with permanent magnets having different bar height, and with partial output gear. 
       FIG. 3   d  is a partial view of the gearing having permanent magnets magnetized in the circumferential direction. 
       FIG. 3   e  is a partial view of the gearing with permanent magnets magnetized in the circumferential direction, in combination with permanent magnets magnetized in the radial direction. 
       FIG. 4  is a perspective exploded view of the output gear with permanent magnets and shielding plate. 
       FIG. 5   a  is a plan view of the drive gear having grooves. 
       FIG. 5   b  is a side view with a partial section of the drive gear having grooves. 
       FIG. 6   a  is a plan view of the drive gear with balls in a ball cage. 
       FIG. 6   b  is a side view with a partial section of the drive gear with balls in a ball cage. 
       FIG. 6   c  is a perspective exploded view of the output gear with a ball cage and balls. 
       FIG. 7  is a spatial exploded representation of a rotary encoder with partial sections. 
   

   DETAILED DESCRIPTION 
   Equally acting components of different exemplary embodiments are provided with identical reference signs in the Figures. 
     FIG. 1   a  is a plan view of drive gear  100  of the gearing according to an example embodiment of the present invention as it is installed as first gear step in a rotary encoder  400  ( FIG. 7 ). Drive gear  100  has a large central bore to accommodate a hollow shaft  401  (shown in  FIG. 7 ), the rotational position of which is measured during operation of rotary encoder  400 . At a front end of drive gear  100 , aligned along a spiral curve in each case, are two longitudinal permanent magnets  101 ,  102  ( FIG. 1   b ), which are arranged at a 180° offset, arranged on top is a spiral-shaped plate  104 , the edges of which extend according to the form of permanent magnets  101 ,  102 . Plate  104  is bonded to permanent magnets  101 ,  102 . Plate  104  is made of a ferromagnetic alloy, so that the magnetic field of permanent magnets  101 ,  102  is intensified. Body  106  of drive gear  100  is made of a ferromagnetic FeNi alloy, which has a relative permeability μ r  of at least 10, and, e.g., of 1000. In the example illustrated, μ r  is approximately 3000. 
   In this exemplary embodiment, the spiral curve is configured as part of an Archimedean spiral according to the equation r=a·φ, r representing the radius of the spiral and a representing a constant positive number. φ should be understood to represent the pivoting angle (in radians) of a radial beam about the pole of the spiral curve. Since the spiral in the illustrated example is centrically arranged with respect to drive gear  100 , the pole is located on axis of rotation  103 . In this type of spiral, two consecutive intersections of an arbitrary beam originating from the pole of the spiral have the same spacing, namely 2·φ·a. 
   Permanent magnets  101 ,  102  and plate  104  are of different thickness in the radial direction, the thinnest regions being at the beginning and the end of permanent magnets  101 ,  102  or plate  104 . 
   As illustrated in  FIG. 1   b , permanent magnets  101 ,  102  are magnetized in the axial direction with respect to drive gear  100 , which means that the connecting line between north pole and south pole of a permanent magnet  101 ,  102  extends substantially in parallel to axis of rotation  103  of drive gear  100 . The two spiral-shaped permanent magnets  101 ,  102  are arranged such that in one permanent magnet  101  the south pole is facing body  106  of drive gear  100 , and in the other permanent magnet  102  it is the north pole. 
     FIG. 1   c  illustrates drive gear  100  with permanent magnets  101 ,  102  and plate  104  in a perspective illustration. 
   As illustrated in  FIGS. 2   a ,  2   b , and  2   c , output gear  200  also includes permanent magnets  201 ,  202 , which are arranged along a circular line  205  at the end face of output gear  200 . As an alternative to a circular line  205 , permanent magnets  201 ,  202  may also be arranged along an ellipsis, for example. Permanent magnets  201 ,  202  may be placed along a circumferential line, which means that a virtual beam, originating from axis of rotation  203  and directed radially outwardly, intersects the circumferential line in every angular position between 0° and 360°. The edge regions of the end faces of permanent magnets  201 ,  202  are beveled in a radially outward direction with respect to axis of rotation  203 , at an angle α, which is 5° in this example ( FIG. 2   b ). Permanent magnets  201 ,  202  are bonded to body  206  of output gear  200 , which is made of a ferromagnetic FeNi alloy and has a relative permeability μ r  of at least 10 and, e.g., of 1000 as in the case of drive gear  100 . In the illustrated example, μ r  is also approximately 3000. This comparatively high relative permeability may significantly intensify the magnetic field. 
   Permanent magnets  201 ,  202  are magnetized in the axial direction (relative to axis of rotation  203  of output gear  200 ) and aligned such that two adjacent permanent magnets  201 ,  202  exhibit opposing magnetization in each case. This means that the north pole of permanent magnet  201  points in the direction of body  206  of output gear  200 , whereas it is the south pole in adjacent permanent magnet  202 . So-called driving pins  204 , made of aluminum, are arranged on output gear  200  between permanent magnets  201 ,  202 . 
   As an alternative, driving pins  204 , instead of being arranged between permanent magnets  201 ,  202 , may be arranged inside permanent magnets  201 ,  202 , rotationally offset by one-half of a pole distance, as illustrated in  FIGS. 2   d  and  2   e . Driving pins  204  are made of a magnetizable material and magnetized themselves as well, having the same alignment and polarity as permanent magnets  201 ,  202 . 
   As an alternative to driving pins  204  in the form of separate components, driving pins  204  may be monolithically integrated within permanent magnets  201 ,  202  by appropriate shaping of the permanent magnets. 
     FIG. 3   a  illustrates drive gear  100  in its operation-appropriate position relative to output gear  200 . During operation, axis of rotation  103  of drive gear  100  and also axis of rotation  203  of output gear  200  are stationary. Due to the fact that axis of rotation  203  of output gear  200  is inclined at an angle α (=5°) with respect to axis of rotation  103  of drive gear  100 , the front-side spacing between drive gear  100  and output gear  200  is of different size depending on the location. Consequently, the magnetic forces between permanent magnets  101 ,  102  of drive gear  100  and permanent magnets  201 ,  202  of output gear  200  are of different magnitude as well, depending on the clearance or the air gap. Furthermore, driving pins  204  are free in the region of the large clearance, which means that their ends do not project into the gaps of spiral-shaped plate  104  in this region. 
     FIG. 3   b  is a perspective partial view of the gearing with drive gear  100  and output gear  200  in the operating position. 
   If drive gear  100  is set in motion, the north pole of permanent magnet  201  virtually “catches” the south pole of permanent magnet  201  of output gear  200  as soon as a sufficiently small air gap or clearance comes about between the poles of permanent magnets  101 ,  201  of drive gear  100  and output gear  200 . In this manner, a force transmission is achieved from drive gear  100  to output gear  200 . Due to the fact that bodies  106 ,  206  of drive gear  100  and output gear  200  are made of a NiFe alloy, which has a relative permeability μ r  of approximately 3000, the magnetic field and thus the transmittable force may be intensified or increased. Furthermore, this effect may be reinforced by ferromagnetic, e.g., magnetically hard sheet  104 , which may lead to a field concentration, which may increase the force yield further. Since the rotary motion about axis of rotation  103  of spiral-shaped permanent magnet  101  has a directional component, which has a tangential orientation with respect to output gear  200 , a torque going out from drive gear  100  is introduced into output gear  200 . The force transmission essentially occurs into the region in which a small air gap prevails. Due to the tilting at angle α, it may be ensured that the sum of all magnetic forces between permanent magnets  101 ,  201  of drive gear  100  and output gear  200  triggers a rotary motion. Since the thickness is uneven in the radial direction of permanent magnet  101  and plate  104  at the beginning and end of permanent magnet  101 , the threading procedure of driving pins  204  into the clearance between the spiral lines may be improved. 
   The reduction ratio of the gearing depends on the number of threads of the spiral line along which permanent magnet  101  extends, on the one hand, and on the number of permanent magnets  201  of output gear  200  able to be brought into operative connection therewith, on the other hand. In the example illustrated, permanent magnet  101  is aligned along a one-gear spiral line, its north pole pointing to output gear  200 . The number of associated south poles or the number of corresponding permanent magnets  201  of output gear  200  is eight. Since the reduction is the quotient of the number of threads of the spiral line and the number of permanent magnets  201  of output gear  200  in reciprocal action thereto, a reduction of 8:1 results in this case. This means that output gear  200  rotates eight times more slowly than drive gear  100  during operation. 
   To optimize the force yield and the synchronism of the gearing, the form of the spiral line of permanent magnet  101  is adapted to the arrangement of permanent magnets  201 . Since the spiral line along which permanent magnet  101  is aligned is configured as Archimedean spiral, the constant clearance between the spiral lines is given as 2·π·a as explained earlier. In the example shown, 2·π·a=4.4 mm, or a≈0.7 mm. 
   The eight permanent magnets  201  of output gear  200  are arranged along a circular curve  205 , so that a circular area is able to be formed by extending outer contour  207  of permanent magnets  201 . The clearances between permanent magnets  201  are adapted to the variable 2·π·a=4.4 mm, e.g., such that one north pole is “caught” by one south pole in every operating position. Expressed in geometrical terms this means that an equilateral octagon having an edge length of 2·π·a=4.4 mm is able to be placed completely inside the afore-described outer contour  207  of the circular area. The action function of the gearing may be provided if the following geometrical criterion is satisfied: According to the number n of homopolar permanent magnets  201  of output gear  200 , an n-gon having an edge length of 2·π·a is formed. This n-gon may be placed on the circular area (each corner onto a permanent magnet  201 ) such that it comes to be completely inside outer contour  207  of the circular area. 
   Analogous relationships with respect to the above statements apply when the antipolar operative connection is examined. Accordingly, second permanent magnet  102  of drive gear  100  is also arranged along a one-gear spiral line. Its south pole interacts with the eight north poles of permanent magnets  202  of output gear  200 . The reduction ratio between permanent magnet  102 , which is aligned along a one-gear spiral line, and the eight corresponding permanent magnets  202  of output gear  200  is thus 8:1 as well. 
   This additional operative connection may therefore not result in a change of the reduction ratio with respect to the afore-described force transmission between permanent magnets  101  and  201 . It may merely serve to increase the force yield or to increase the transmittable torque since permanent magnets  101  and  102 , in interaction with permanent magnets  201  and  202 , work virtually in parallel with one another. In particular when the gearing is to be used in rotary encoders, this parallel method of operation of north-pole and south-pole couplings may be provided since the danger of an asynchronous operation, i.e., slippage between drive gear  100  and output gear  200 , should be avoided within the meaning of a precise measurement. 
   Using the gearing as described herein may allow the required torque to be transmitted without any contact whatsoever. However, to safeguard against possible asynchronous, i.e., slip-encumbered, operating states, the non-magnetic driving pins  204  of aluminum are additionally used in output gear  200  in the example illustrated. Instead of aluminum, some other non-magnetic material such as brass or bronze, but also a plastic such as PTFE or PA, etc., may be used as well. Furthermore, as mentioned earlier, driving pins  204  may be magnetized as well and thus may be made of a magnetic material. These driving pins  204  are provided to move output gear  200  in a synchronous and non-slip manner with respect to drive gear  100  even if the power coupling via permanent magnets  101 ,  102 ,  201 ,  202  should no longer be sufficient to transmit the torque. This danger may arise for example when torque spikes occur in high angular accelerations, but also in the presence of an interference magnetic field or when vibrations occur. Plate  104  may ensure that the driving pins will not contact permanent magnets  101 ,  102  of drive gear  100  since driving pins  204  have such short dimensions that they do not reach permanent magnets  101 ,  102 . In the event that the occurring torque is so great that driving pins  204  come to have an effect, the contacting force transmission occurs between driving pins  204  and plate  104 . Possible wear of permanent magnets  101 ,  102  may be avoided in this manner. 
   As mentioned previously already, driving pins  204  are magnetized in the exemplary embodiment illustrated in  FIG. 2   e . In this case, a torque may already be transmitted even without contact or at reduced contact pressure at plate  104  or at permanent magnets  101 ,  102 . 
   Furthermore, wear of a gearing according to the described example may be negligible since a contactless force transmission takes place during normal operation. 
   As an alternative to the described exemplary embodiment, plate  104  may also be omitted. In this case, the edges of permanent magnets  101 ,  102  of drive gear  100  may be provided with a hard material layer, or composites may be used. 
     FIG. 3   c  illustrates another exemplary embodiment, which is distinguished in that permanent magnets  101 ,  102  have different bar heights H, h. In this case, permanent magnets  201 ,  202  engage between permanent magnets  101 ,  102  without making contact with the magnets during normal operation of the gearing. A corresponding force is transmitted by the attractive and repulsive forces of permanent magnets  101 ,  102  of drive gear  100  and permanent magnets  201 ,  202  of output gear  200 . In the event that the gearing is subjected to excessive stress, a force is mechanically transmitted via contact with permanent magnets  101 ,  102 ,  201 ,  202 . To reduce wear for this emergency operation, appropriate hard material coatings are provided here. This function is also aided by the conical shape of permanent magnets  201 ,  202  of output gear  200 . 
   Other geometric forms, which deviate from a cylindrical form, may also be selected for driving pins  204  of the other exemplary embodiments, for example, to improve the emergency-running properties. 
     FIG. 3   d  illustrates an additional exemplary embodiment of the gearing in which permanent magnets  101 ,  102  are magnetized in the radial direction and permanent magnets  201 ,  202  are magnetized in the circumferential direction. Accordingly, in each case four magnetic poles are arranged opposite each other per permanent magnet  101 ,  102 ,  201 ,  202  in the gearing. In the case of a relative displacement between permanent magnets  101 ,  102  of drive gear  100  and permanent magnets  201 ,  202  of output gear  200  as a result of the torque to be transmitted, the magnetic forces of the poles will counteract this displacement, thereby resulting in a relatively stiff power-transmission characteristic of the gearing. 
   In an additional example embodiment of the gearing, permanent magnets  101 ,  102  illustrated in  FIG. 3   e  may be magnetized in the radial direction, as in the previous exemplary embodiment, but such that poles of the same type are arranged opposite one another. In the example illustrated, the north pole of permanent magnet  101  is arranged across from the north pole of permanent magnet  102 . In contrast, permanent magnets  201 ,  202  of output gear  200  are magnetized in the axial direction. Furthermore, analogously to  FIG. 2   e , driving pins  204  are magnetized as well, e.g., such that the north pole of a driving pin  204  projects between the two north poles of permanent magnets  101 ,  102  of drive gear  100 . During operation, the south pole of permanent magnet  202  of output gear  200  is thus attracted by the two north poles of permanent magnets  101 ,  102 , so that the system strives for the shortest distance between the poles having different polarization. This function is aided by the repelling forces between the north pole of driving pin  204  and the north poles of permanent magnets  101 ,  102 . In this arrangement, driving pins  204  may thus contribute to the centering of output gear  200  relative to permanent magnets  101 ,  102  of drive gear  100  and may ultimately lead to an increase in the torque transmittable in a contactless manner. 
     FIG. 4  illustrates an additional exemplary embodiment in which the force transmission is performed via permanent magnets  101 ,  102 ,  201 ,  202 . However, in this case an arrangement is selected in which axes of rotation  103 ,  203  of drive gear  100  and output gear  200  are aligned in parallel. This may be advantageous, for example, for the subsequent gear steps since it may allow the axes of all gear wheels to be aligned in parallel with respect to axis of rotation  103 , so that no bevel-gear step or similar device may need to be used. 
   The parallel alignment of axes of rotation  103 ,  203  may be made possible by a screening plate  300  into which a window  301  is introduced. Screening plate  300  is also made of a NiFe alloy having comparatively high relative permeability, which has the property of significantly weakening magnetic fields. As an alternative, it is also possible to utilize an SiFe alloy or amorphous or nanocrystalline alloys, etc., having high relative permeability. In this manner, the magnetic coupling between drive gear  100  and output gear  200  may spatially be limited to the area of window  301 . The remaining area of output gear  200  is magnetically insulated to a large extent by screening plate  300 , so that the transmittable torque is virtually zero in this region. 
   As an alternative to a circumferential annular shape of screening plate  300 , it is also possible to select only a ring-segment form which covers only the relevant effective area. 
   A system illustrated in  FIGS. 5   a  to  6   c  is described in the following as an exemplary embodiment in which the force-transmission element of drive gear  100  is a groove  101  aligned along a spiral line. Balls  208 , which are stored in a ball cage  201  of output gear  200 , engage with this groove  101 . As illustrated in  FIG. 6   b , ball cage  201  is arranged such that, on the one hand, balls  208  are able to rotate freely therein about all axes and are axially secured against falling out, on the other hand. In the illustrated example, ball cage  201  or entire output gear  200  is made of plastic, so that balls  208  may be installed in ball cage  201  by snapping into place. 
   As illustrated in  FIG. 6   a , output gear  200  has sixteen balls  208 , which interact with a groove  101  (single-gear spiral). On the basis of this information the reduction ratio of 16:1 may be determined. 
   In this exemplary embodiment, axis of rotation  103  of drive gear  100  is tilted with respect to axis of rotation  203  of output gear  200  in the assembled state. In contrast to the exemplary embodiments illustrating contactless force transmission, there are friction losses and wear in this example of a contacting force-transmission device. These effects may be reduced by lubricating the gearing and by using suitable material pairings. Wear may be reduced in that the rolling partners, e.g., groove  101 , balls  208  and ball cage  201 , are provided with a wear-reducing hard-material coating such as a tungsten-carbide layer in combination with slideable plastics, such coating being applied to all or some of the mentioned components. Ball cage  201  may be manufactured from sintered metal with incorporated lubricants. As an alternative, balls  208  and/or the other rolling partner may be made of a ceramic material. 
   As illustrated in  FIG. 7 , the gearing is installed in a multiturn rotary encoder  400  for ascertaining the absolute angular position. Via its large central bore, drive gear  100  of the gearing is connected to a hollow shaft  401  of rotary encoder  400  in a rotatably fixed manner. Hollow shaft  401  holds a shaft in a rotatably fixed manner, the rotational position of which is to be measured during operation of rotary encoder  400 . Mounted at a shoulder of hollow shaft  401  is a code disk  402 , which is bonded in this example, so that during measuring operation code disk  402  rotates with the same frequency as hollow shaft  401 . To record the absolute position within one rotation of hollow shaft  401 , code disk  402  carries a multi-track code, e.g., a Gray code, the finest track being a high-resolution incremental track which may be positioned as far as possible outside at the periphery of code disk  402 , to permit the arrangement of as many graduation periods as possible over the periphery. The more graduation periods are disposed across the entire circumference, the higher the angular resolution of the rotary encoder to be detected. 
   Positioned in non-rotating housing  410  of rotary encoder  400  are a light source  411 , a lens  412  and a scanning plate  413 . Furthermore, a wafer  414  on the underside of which photodetectors are affixed, is joined to housing  410  in a rotatably fixed manner. With the aid of this optical angle scanner the individual angular position within one rotation of hollow shaft  410  is determined in an incremental and/or absolute manner. 
   A multiturn measurement may require the gearing and the additional gear steps cooperating therewith. These are integrated in a gear box  420 , the outer wall of which is partially omitted in  FIG. 7  for clarity. Gear box  420  is joined to housing  410  in a rotatably fixed manner and thus does not participate in the rotary motion of hollow shaft  401  or drive gear  100 . In contrast, axis of rotation  203  of output gear  200  is immoveable also with respect to gear box  420  and thus with respect to housing  410 . Drive gear  100 , in a slip-free manner and at the given reduction, transmits the rotary motion of hollow shaft  401  to output gear  200 , which is supported in bearing P so as to allow rotation about axis of rotation  203  relative to gear box  420 . A gear wheel, which meshes with a gear wheel of an additional reduction step, is connected to output gear  200  in a rotatably fixed manner. Mounted on the shaft of this additional reduction step is a graduated disk  421  having magnetic graduation. Furthermore, additional gear steps having further graduated disks  422  and  423  are arranged accordingly. The axes of rotation of graduated disks  421 ,  422 ,  423  are aligned in parallel with hollow shaft  401 . Each graduated disk  421 ,  422 ,  423  is made up of a magnetic body having magnetic poles (north, south) arranged by turns in the circumferential direction. In the simplest case, graduated disks  421 ,  422 ,  423  each take the form of short bar magnets having a single north pole and south pole. The magnetic graduations of graduated disks  421 ,  422 ,  423  are arranged in a common plane. 
   In this example, graduated disk  421  rotates more slowly than hollow shaft  401  by a factor of 16, the additional gear steps leading to a further reduction of the rotational frequencies of corresponding graduated disks  422 ,  423 . 
   Via detector devices at the upper side of wafer  414 , which are Hall sensors in this case, the angular positions of graduated disks  421 ,  422 ,  423  are determined. Graduated disks  421 ,  422 ,  423  thus measure the number of rotations of hollow shaft  401 , each graduated disk  421 ,  422 ,  423  being driven in a geared-down manner via the reduction gear by the particular gear step connected upstream. For a space-saving design, graduated disks  421 ,  422 ,  423  as well as pivot bearing P of axis of rotation  203  of output gear  200  are arranged within the peripheral region of code disk  402 . 
   Instead of Hall sensors, it is also possible to use magneto-resistive sensors such as AMR, GMR (giant magneto-resistive) or TMR sensors (tunnel magneto-resistive), etc., as detector devices. 
   Output gear  200  is installed between drive gear  100  and wafer  414  in the described example. Because of this configuration and due to the fact that the magnetic graduations of graduated disks  421 ,  422 ,  423  are arranged in one plane, it may be relatively easy to accommodate the associated detector devices on the upper face of wafer  414 . As described above, the corresponding photodetectors are affixed to the underside of wafer  414 . Both sides of wafer  414  may be fitted with electronic components, which may provide certain advantages with respect to the required space and also the production economy. 
   The components of the optical scanner (e.g., light source  411 , lens  412 , sampling plate  413  and code disk  402 ) are thus situated underneath wafer  414  in rotary encoder  400  illustrated in  FIG. 7 , the photoelements being affixed to the underside of wafer  414 . Mounted on the upper face of wafer  414  are, among others, the detector devices for recording the rotational positions of graduated disks  421 ,  422 ,  423 . As illustrated in  FIG. 7 , the gearing and the additional gear steps are mounted above the wafer. Output gear  200 , which similar to drive gear  100  is part of the novel gearing, does not project beyond the outer diameter of housing  410 . In this case, it is possible to use a housing  410  of a conventional rotary encoder since, compared to earlier gearings, the gearing may not enlarge the radial dimensions of rotary encoder  400 . Disposed above output gear  200  is drive gear  100  of the gearing, which is dimensioned such that its diameter is not greater than that of housing  410 . Due to the described arrangement, it is therefore possible to produce a rotary encoder  400  which may have exceedingly small structural dimensions both in the radial and the axial direction and may be equipped with a gearing that may have the already described advantages. 
   As mentioned previously, it may be provided in the described configuration that output gear  200  is arranged such that it does not project, or projects to only a negligible degree, beyond the outer diameter of body  106  of drive gear  100 . In other words, the clearance between bearing P and axis of rotation  103  of the drive gear is not greater than one-half of the outer diameter of body  106  of drive gear  100 . In the example illustrated, the clearance between bearing P and axis of rotation  103  of the drive gear is also not greater than one-half of the outer diameter of code disk  402 . In the event that two or more bearings P are provided in which axis of rotation  203  of output gear  200  is supported, the particular bearing P having the shortest clearance with respect to axis of rotation  103  may be considered in this examination, provided axis of rotation  203  of output gear  200  is arranged in a correspondingly inclined manner with respect to axis of rotation  103  of drive gear  100 . As a result of satisfying these criteria, the arrangement of the rotary encoders may have a relatively small diameter. 
   The use of the gearing is not limited to rotary encoders whose incremental scanning is based on an optical principle or whose counting of rotations is based on a magnetic scanning principle. It also covers, among others, rotary encoders having a capacitive or an inductive effect.