Abstract:
To enable signals to be transmitted from a fixed machine part to a machine part opposite same which rotates on a hollow shaft or vice versa, light must be able to be transmitted or received over the entire circumference. This is achieved by using an optical waveguide which, unlike conventional optical waveguides, is designed to couple out some of the light passing through it and, conversely, to allow light to enter, at any locations on its circumference.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of European Patent Office application No. 07024402.5 EP filed Dec. 17, 2007, which is incorporated by reference herein in its entirety. 
     FIELD OF INVENTION 
     The invention relates to a machine as claimed in the claims. 
     BACKGROUND OF INVENTION 
     The machine therefore has a first machine part and a second machine part, and the second machine part can be rotated relative to the first machine part about an axis of rotation. Data signals are optically transmitted, i.e. an optical signal transmitting device is disposed on one machine part and a device for receiving optical signals is disposed on the other machine part. It is rarely possible to dispose an optical transmitter and an optical receiver precisely in the axis of rotation. If optical signals are now to travel from an optical transmitter to an optical receiver outside of the axis of rotation, the problem is that the optical signals must be transmitted at any angular positions of the second machine part. This problem has hitherto been solved by providing a plurality of light sources and ensuring by constructional means that the light rays emitted by the light sources spread out to form a luminous ring at a particular location in the machine. The optical receiver can be a point detector. When the rotating machine part rotates, it is then always ensured that light passes from the optical transmitter to the optical receiver. 
     SUMMARY OF INVENTION 
     Due to the fact that the light rays from the optical sources must be spread in order to form a luminous ring, a certain distance must be provided for the ray path. This means that, in the machine, space must be provided for a cylinder of a particular length in which the light is guided until it is emitted as a ring on an edge of the cylinder. The plurality of light sources also takes up a relatively large amount of space in the machine. 
     An object of the invention is to provide a machine of the generic type mentioned in the introduction which is of relatively short construction (referred to the axis of rotation) and therefore of compact design. In particular, the machine shall be able to incorporate a hollow shaft, i.e. for the transmission of data signals beyond the axis of rotation. 
     This object is achieved by a machine having the features set forth in the claims. One of the machine parts is thus provided with an annular optical waveguide which is disposed concentrically with respect to the axis of rotation and has the characteristic of allowing some of the coupled-in light to emerge or, conversely, of allowing light to enter from outside. The design and arrangement of the annular optical waveguide must be such that the light emerging from the optical waveguide reaches the other machine part, i.e. the part where the optical waveguide is not disposed, or that the light emitted by the other machine part can enter. 
     According to an explicit embodiment of the invention, the optical waveguide is part of the device for receiving optical signals. However, in a particularly simple embodiment the optical waveguide is part of the optical signal transmitting device, said optical signal transmitting device comprising a light source which can couple light in at a coupling point. 
     As a result of the optical waveguide being provided there is no necessity to use a plurality of light sources. No space is required for the spreading of the light ray emitted by the light source. In fact the optical waveguide and associated light source can be disposed in very close axial proximity to an optical signal receiving device, so that the machine is of short construction. 
     There are different methods of ensuring that light emerges from the optical waveguide. An exit point can be specified in a defined manner whereby, in the case of an optical waveguide comprising in per se known manner a core and a cladding with the material constituting the core having a lower refractive index than the material constituting the cladding, the cladding is broken all round the circumference of the optical waveguide ring (i.e. not over the cross-section of the optical waveguide, but around the circumference defined concentrically to the axis of rotation). This can be particularly simply implemented as a continuous slit in the cladding. 
     In another embodiment, a plurality of scattering centers is implemented in the optical waveguide. These are designed to diffract the light not randomly, but in a predefined direction from the optical waveguide and are therefore oriented in a predefined manner in the optical waveguide. Such scattering centers can be implanted in an optical waveguide core e.g. using a laser. 
     Finally it is also possible to provide one side of the optical waveguide with indentations which cause the light normally reflected by that side to be sent out obliquely, namely toward the side of the optical waveguide opposite the indentations, where the machine part on which the optical waveguide is not disposed must be arranged, i.e. generally the machine part incorporating the receiving device. 
     The optical signals from the optical signal transmitting device can be transmitted axially (with respect to the axis of rotation of the second machine part) to the receiving device in the conventional manner. However, using the optical waveguide also makes it possible, e.g. by suitably positioning the breaks in the cladding of the optical waveguide, to transmit the light radially, i.e. so that light is coupled out over the entire circumference of the optical waveguide ring. The non-rotating machine part can then be disposed radially around the rotating machine part, thereby enabling the machine to be of particularly short construction in the axial direction. 
     As already mentioned, the invention is particularly suitable in the case where the second machine part rotates via a hollow shaft, the optical waveguide then only needing to surround the hollow shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Particular embodiments of the invention will now be described with reference to the accompanying drawings in which: 
         FIG. 1  shows a plan view of one of two machine parts of a machine and 
         FIG. 2  shows a cross-sectional side view of a machine, 
         FIGS. 3 and 4  illustrate a first embodiment of an optical waveguide in different cross-sections, 
         FIG. 5  illustrates a second embodiment of an optical waveguide in a longitudinal section through the optical waveguide and 
         FIG. 6  and  FIG. 7  illustrate a third embodiment of an optical waveguide in different cross-sections, 
         FIG. 8  to  FIG. 10  illustrate different possibilities for coupling in optical signals for the optical waveguides, 
         FIG. 11  shows a variant of the embodiment shown in  FIG. 1  and 
         FIG. 12  shows an alternative embodiment of a machine. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     In a machine, part of which is shown in  FIGS. 1 and 2 , data is transmitted from a fixed component to a component which rotates relative to said fixed component. The rotation takes place in particular via a hollow shaft  10  which is mounted via bearings  12  in a housing  14 . Fixedly connected to the housing  14  is a mount  16  for devices used for electronic data processing. The mount  16  can be implemented as a circuit board, or the electronic components can be provided on a ceramic substrate. Corresponding to the mount  16 , which is fixed to the housing  14 , is another mount  18  which is coupled to the hollow shaft  10  and rotates with same. An optical signal transmitting device is disposed on the mount  16 , while a device for receiving optical signals is disposed on the mount  18 . 
     The optical signal transmitting device and the receiving device must be suitably arranged with respect to one another such that data signals reach the receiver at any angle of rotation of the hollow shaft  10 . In the embodiments shown in  FIGS. 1 and 2 , this is effected in such a manner that the optical signal transmitting device emits light over its entire circumference, whereas a point optical receiver is used. However, the invention can also be similarly applied to a point light source and an annular detector. In the present case, light is emitted from an optical waveguide  20  into which light is coupled by a light source not shown in  FIGS. 1 and 2 . Conventional optical waveguides are designed so that no light escapes from them. In the present case, a conventional optical waveguide is modified such that at least some of the light coupled in by the light source does actually escape, a suitable measure being taken to ensure that light escapes over its entire circumference. There is therefore no angle at which no light escapes from the optical waveguide  20 . 
     There are various ways of implementing this emission of light from an optical waveguide.  FIG. 3  shows a cross-section through an optical waveguide and  FIG. 4  the same optical waveguide in untwisted form, wherein the horizontal axis constitutes the angle. The optical waveguide  20   a  from  FIG. 3  or  FIG. 4  has a core  22  which is made e.g. of polymer fiber and is surrounded by a cladding  24  having a higher refractive index than the polymer fiber. Because of the higher refractive index of the cladding, a light ray  26  is reflected by the cladding  24 . The optical waveguide  20   a  differs from conventional optical waveguides in that the cladding  24  has a break  28 . This break  28  extends, as shown in  FIG. 4 , over the entire angular range. As the cladding  24  is broken, a light ray  30  emerges at the break  28 . The break  28  is now arranged such that the light ray  30  emerges axially (referred to the axis of rotation  32  of the hollow shaft) and light is therefore transmitted to the receiver  32  on the mount  18 . 
     In the case of an optical waveguide  20   b  as shown in  FIG. 5 , the cladding  24  is unbroken. In contrast there is disposed in the optical waveguide core  22  a plurality of scattering centers  34  at which a light ray  36  is scattered. In this case the scattering centers  34  are oriented such that the light ray  36  is deflected in such a way that its deflection, as light ray  38 , is essentially perpendicular to the cladding  24  so that it is not reflected by same, but escapes from the cladding  24 . 
     The scattering centers  34  can be implemented in the optical waveguide core  22  by the application of heat using a laser. 
     The perpendicular exit of a light ray  40  from a cladding  24  is also provided for in an optical waveguide  20   c  as shown in  FIGS. 6 and 7 . For this purpose a plurality of indentations  42  are made in the optical waveguide  20   c , namely on the side opposite the nominal exit side of the light ray  40 . Indentations  42  deflect a light ray  44  propagating in the optical waveguide  20   c  such that it is perpendicularly incident on the cladding  24 , penetrate same and exits as light ray  40 . In order to keep the exit cone small, the optical waveguide  20   c  is flattened on the exit side, cf. surface  46 . 
     Now that three different embodiments  20   a ,  20   b ,  20   c  of the optical waveguide have been described with reference to  FIGS. 3 to 7 , attention will now be turned to the coupling of a light ray into the optical waveguide. In the present case this involves implementing the coupling-in of the light ray such that the optical waveguide  20  is not interrupted at any angle so that it would not emit light at that angle. It must be ensured that the optical waveguide emits light over its entire circumference. 
       FIG. 8  illustrates an embodiment in which a light source  48  is disposed radially outside the optical waveguide  20 . In the present case, the optical waveguide  20  does not form a completely closed ring, but has an obliquely cut first end  50  and an obliquely cut second end  52 , the ends  50  and  52  being brought together. The light source  48  transmits light perpendicularly, i.e. radially to the axis of rotation  32  of the hollow shaft  10 , onto the obliquely cut end  50 , and a light ray  54  emitted in this way is deflected at the obliquely cut end  50  to form the light ray  56  and propagates further in the optical waveguide  20 . 
     In the embodiment according to  FIG. 9 , an optical waveguide  20  has, at one end, a coupling-in branch  58  which has a much smaller cross-section than the optical waveguide  20  overall. The other end of the optical waveguide  20  abuts the first end of the optical waveguide  20  above the coupling-in branch  58 . A light source  48  can now couple light into the coupling-in branch  58  such that it propagates in the entire optical waveguide  20  after passing through a transition region  60 . At the other end of the optical waveguide  20 , just a little light escapes at a projecting location  62 , but most of the light is transmitted from one end of the optical waveguide  20  to the other so that the light can pass through the optical waveguide in a multiple manner. 
     In an embodiment as shown in  FIG. 10 , an optical waveguide  20  is multiply wound over the circumference of a circle. This enables the optical waveguide  20  to have a different, in particular a smaller, cross-section than the optical waveguide from  FIGS. 8 and 9 . This means that no special coupling-in arm  58  as in  FIG. 9  is required, but light can be coupled in over the entire cross-section of the optical waveguide  20  by a light source  48 . 
     Unlike normal prior art practice, the invention only needs one light source, and it is the optical waveguide  20  that distributes the light evenly over its circumference. However, the invention does not exclude the possibility of using a plurality of light sources  48  which are distributed over the circumference. This is shown by way of example in  FIG. 11 . 
       FIG. 12  shows an alternative embodiment of the invention. It differs from the embodiment in  FIG. 2  in that the fixed mount  16  radially encloses the mount  18  that rotates with the hollow shaft  10 . The optical waveguide  20  emits light, not in the axial direction, but radially to the axis of rotation  32  of the hollow shaft to the receiver  32  on the mount  18 . The embodiment according to  FIG. 12  is of particularly short construction.