Abstract:
A clock with a twenty four hour display includes a minute hand, a second hand, a minute scale, a date display, and an hour scale on a first conchoid. The first conchoid includes an outer loop for the hours of the day from 6-18 hours and an inner loop for the hours of the day from 18-6. A crossing point of the inner and outer loops is established at the hours of 6 and 18. To achieve unambiguous indication, the hour hand is made variable in length. In a second conchoid offset by a constant amount radially inwards with respect to the first conchoid, which for instance is milled in the form of a groove in the dial, a guiding element is moved azimuthally through the inner part of the hour hand, which receives an overlay of radial movement owing to the shape of the second conchoid. The second conchoid and the guiding element may be covered by a disc joined to the inner part of the hour hand and turning with it.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention concerns a clock, driven by a mechanical, electrical or electronic motor, with analog and unambiguous 24 hour display. 
     2. Description of the Related Art 
     Several clocks with an analog and unambiguous 24 hour display are known, for instance from DE 267 810 (D1), U.S. Pat. No. 5,696,740 (D2), WO 91/03774 (D3). 
     Both in D 1  and in D 2  the 24 hour unambiguity is obtained by means of two concentric number scales each of 12 hours, where the first 12 hour group comprises the times from 0-12 o&#39;clock, the second the time from 12-24 o&#39;clock. On the transfer from one scale to the other the hour hand always changes its position in an abrupt manner; it either travels outwards or is shortened. 
     In D 3  the unambiguity of the display of the hours is addressed similarly in that two concentric 12-hour scales are arranged on the dial, at the same time however a transparent disc is present which has a period of revolution of 24 hours and—in one embodiment—has two semicircular shaped covers, which cover the nonapplicable hour values. 
     Further documents though not under consideration here—(i.e. DE 33 05 414 and DE 40 376 57) show clocks with so-called pseudo-analog presentation, where using electronic auxiliary means, such as LEDs and liquid crystal displays, an unambiguous 24-hour display is, created. 
     The arrangements published in D 1  and D 2  for the changing of the length of the hour hand require either additional energy from the clock motor for tensioning a spring (D 1 ) or an additional source of energy (D 2 ). The solution proposed in D 3  shows the hours at all times of the day and night on two semi circles of different radius. Neither in terms of technical producibility nor in market acceptance were these solutions able to succeed. 
     Although it would be possible with the means described, the transfer from one scale to the to the other was never chosen to be other than at midday and midnight. 
     Further, clocks have become known, which have noncircular scales, such as for instance in DE 196 41 885 (D 4 ), DE 299 03 950 (D 5 ) and DE 299 34 451 D6). Whilst in D 4  an hour indicating element is moved on any desired curve as a guiding element, in D 5  the indicating element is guided on cycloids, which are generated by a four joint drive, by means of an additional gear wheel, means are described here to move the aforesaid indicating element on non-circular tracks, but a 24-hour indicator of an unambiguous nature is not published therein. 
     BRIEF SUMMARY OF THE INVENTION 
     It is therefore the aim of the present invention to move the hour marking indicating element—whether this is the hour hand or a clear and unmistakable element—on a track of this construction, which permits an unambiguous arrangement of the positions of the indicating element during the 24-hour passage of the day and so by its position effects a conspicuous difference between the daytime and night-time hours without the need to alter the customary angular positions of the indicator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The inventive idea is more closely explained using the attached drawing in several embodiments. 
     Shown are: 
     FIG. 1 the plan view of a first embodiment, 
     FIG. 2 a part of FIG. 1, with a first embodiment of a guide element, 
     FIG. 3 a longitudinal section through the embodiment in FIG. 1, 
     FIG. 4 a detail from FIG. 3 with a second embodiment of a guide element, 
     FIG. 5 a second embodiment in a schematic longitudinal section, 
     FIG. 6 the embodiment in FIG. 5 in a schematic plan view. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a plan view of a first embodiment of a clock according to the invention. Along with conventional and here adopted elements, such as a minute hand  1 , second hand  2 , date display  3  and a conventional circular minute scale  4 , an hour hand  5  with variable length is shown. The point of the hour hand  5  runs around a two-loop enclosed curve, such as a first conchoid  7 , with an outer loop  8  and an inner loop  9 , which have a crossing point  6 . The daytime hours from 6 to 18 hours are allocated to the outer loop  8  and the night-time hours from 18 to 6 hours to the inner loop  9 . Since these allocations are only of a graphical nature, they can obviously be reversed. On such two-loop curve is for instance the conchoid, also called the Pascal snail curve, (described, for instance, in Karel Rektorys, applicable Mathematics, Cambridge, Mass., USA 1969). FIG. 1 includes the representation of a second conchoid  10 , shown dashed, which is derived by a constant radial offset from the curve  7  with an outer loop  8  and an inner loop  9 . This second conchoid  10  is shown dashed because it can be covered by a disc  11 ; it is formed as a guide curve and together with the guiding elements is more clearly explained in FIG.  2 . 
     FIG. 2 is the representation of only the inventive part of the clock. The disc  11  is shown here only dashed and transparent and allows a clear view of the conchoid  10  lying below and covered by the disc  11 . The hour hand  5  is, as was already seen in FIG. 1 constructed from two parts. Its outer part, referenced with the reference  13 , is joined in a pivoting manner to a sliding element  12 ; this sliding element  12  lies in the for instance groove shaped conchoid  10  and follows the track of this conchoid during the circulation of the inner part of the hour hand  5 . This inner part of the hour hand  5  carries the reference  14 , and is joined firmly to the disc  11 . The disc  11  thus completes a revolution in 12 hours, together with the inner part  14  of the hour hand  5  The sliding element  12  is formed in this embodiment in a sickle shape such that the radius of curvature of the outer-lying surface is smaller than the smallest radius of curvature of the outer surface of the conchoid  10 , and that of the inner lying surface is greater than the greatest radius of curvature of the inner surface of the conchoid  10 . The longitudinal extension of the sliding element  12  measured in the tangential direction is made large enough so that at the crossing point of the two loops, of the conchoid  10  (which carry the references  15 ,  16 ) the sliding element  12  is guided securely from the outer loop  15  to the inner loop  16 , or from the inner loop  16  securely onto the outer loop  15 . 
     FIG. 3 is a longitudinal section through the embodiment of FIG. 1 for instance at 24 hours. A dial  24  serves here in the sense of a non-limited example of a mounting platform for all further named and yet to be named elements. This element named below as dial  24  can be attached either to the works, or the case. It is only essential that in the operation of the clock the relationship to the actual dial is fixed. The conchoid  10  with its outer loop  15  and its inner loop  16  is worked into the dial  24  for instance by milling. A hollow shaft, called the hour tube  18 , is mounted within the dial  24 , with which the disc  11  and the inner part  14  of the hour hand  5  are joined firmly. For stability reasons the inner part  14  of the hour hand  5  is joined to the disc  11  for instance with a support  19 . The disc  11  has a radial slit  20  running parallel to the inner part  14  of the hour hand  5 . A guide pin  12 , with which the outer part  13  of the hour hand  5  is joined to the sliding element  12 , can move in this slit  20 . The sliding element  21  is thus moved in an azimuthal direction by the disc  11 . The guide pin  21  is for instance firmly fixed to the sliding element  12  and mounted in the outer part  13  of the hour hand  5  so as to pivot about its long axis. In accordance with the invention this can however also be arranged so that the guide pin  21  is firmly fixed to the outer part  13  of the hour hand  5  and mounted on the sliding element  5  so as to pivot about its long axis. 
     The outer part  13  of the hour hand  5  is arranged so as to be able to slide in the longitudinal direction with respect to its inner part  14 , for which arrangement several solutions are known and not to be described here. 
     The remaining elements, such as the minute tube  22  with the minute hand  1  and the second axle  23  with the second hand  2  are known and only mentioned for completeness. The concept of the dial can be widely interpreted here; the decision as to which and whether figures appear on it is purely of an aesthetic nature. The technical significance of the dial  24  lies in its characteristic as, a baseplate for all the previously mentioned elements in the sense of the previous description. 
     A section of the conchoid  10  is shown in FIG. 4, together with a further embodiment of sliding element  12  from FIG. 2,  3  named a-guide element  17 . This comprises a carrying member  25  and here for instance three wheels  26 ,  27 ,  28  rotatably mounted within it. Their arrangement is selected such that the middle wheel  26  lies outside, so that it can touch the outer surface of the conchoid  10 ; the other two wheels  27 ,  28  can touch the inner surface of the conchoid  10 . The arrangement of the three wheels  26 ,  27 ,  28  is further so designed that the guiding element  17  both in that part of the conchoid  10  with the greatest radius and also that with the smallest it can be moved with radial play in the tangential direction. In the region of the middle wheel  26  the carrying member  25  carries the guide pin  21 , for which the same applies as previously stated under FIG.  3 . 
     Also included in FIG. 4, however dotted, is a modification of the carrying member  25 . One arm  29  of the carrying member  25  is constructed as a flexing spring  30 , so that all three wheels  26 ,  27 ,  28  can always touch the side surfaces of the conchoid  10  assigned to them. Alternatively both arms of the carrying member  25  can be constructed as flexing springs  30 , whereby the applied pressure of the wheels  26 ,  27 ,  28  onto the side surfaces can be better apportioned. 
     The length of the guiding element  17 , that is the separation of the wheels  27 ,  28  is chosen such that the crossing point of the two loops  15 ,  16  of the conchoid  10  can be passed in the correct sense. The number of wheels  26 ,  27 ,  28  can obviously be chosen to be different, for instance larger, with a corresponding adaptation of the form and construction of the carrying member  25 . 
     FIGS. 5 and 6 are representations of a second embodiment for the guidance of the point of the hour hand  5  onto the two-loop curve  7  provided. FIG. 5 is a section perpendicular to the plane of the dial  24 , FIG. 6 a plan view. For a better understanding, FIG. 5 is produced so that all the sequential axes lie in the same plane, which actually is never; the case. 
     In FIG. 6 a two-loop curve (also called a Pascal snail)  31  is shown dashed, with an outer loop  40  and an inner loop  41  and a crossing point  42 . This corresponds functionally to the conchoid  10  from FIG.  2  and also in so far as it at least indicates the track of the guide pin  21  in so far as that obviously a radial offset: by a constant, or also by a variable amount—for instance proportional—is included within the inventive idea. This curve  31  is generated in this embodiment by the interworking of several gear wheels and guide arms, as set out below: Firmly fixed to the dial 24—or the assembly platform corresponding to it—is a gear wheel A with radius r(A), coaxial with the hour tube  18 . The hour tube  18  carries an arm  32 , circulating with it, in which an axle  36  of a second gear wheel B with radius r(B) is mounted, whereby: 
     
       
           r ( B )= 2   r  ( A )  equation (1) 
       
     
     Further these radii and the crossing point  42  of the two loops  40 ,  41  of the curve  31 —whose distance from the centre of the hour tube is designated d( 31 )—are connected such that 
     
       
           r ( A )+ r ( B )= d ( 31 )  equation (2) 
       
     
     The arm  32  can be a flat-formed component in a plane parallel to that of thee gear wheels. It carries here, firmly fixed to it, a third gear wheel C with radius r(C), which meshes-with a fourthgear wheel D 1  with radius r(D 1 ), which is mounted on an axle  33 . This is mounted in a second arm  34 . The second arm  34  sits firmly on the axle  36  of the second gear wheel B and therefore runs around with this. The axle  33  of the fourth gear wheel D 1  carries—similarly joined firmly to it—a fifth gear wheel D 2  with radius r(D 2 ) which meshes with a sixth gear wheel E with radius r(E). This sixth gear wheel E is mounted on an axle  35 , which is fastened on the second arm  34  at a distance d(E) from the axle  36  and runs parallel to all the previously mentioned axles. The sixth gear wheel E carries at a distance d(F) from the axle  35  the guide pin  21  running parallel to the axles  33 ,  36 . 
     The following equations apply for the further named radii and distances: 
     
       
           r ( D   1 )= 1 / 2   r ( C )  equation (3) 
       
     
     
       
           r ( E )= r ( D   2 )  equation (4) 
       
     
     
       
           d ( E )= d ( F )  equation (5) 
       
     
     Whilst the crossing point  42  of the two loops  40 ,  41  is fixed by equation (2), the two loops  40 ,  41  themselves are only defined by the equations (3), (4), (5) and (6): 
       d ( 40 )− d ( 41 )= 4   d ( E )  equation (6) 
     The choice of r(C) is not dependent on r(A), but purely opportunistically based on the available space, with the limitation that—if the hour tube  18  is given the radius r( 18 ) 
     
       
           R ( C )&lt; r ( A )+ r ( B−r ( 18 )  equation (7); 
       
     
     The disc  11  and the outer and inner parts  13 ,  14  of the hour hand  5  are, not shown in FIG. 5,  6 . All these elements can be arranged as shown in the first embodiment. 
     As a modification to this the actual dial  24  can be made at least partly transparent and arranged such that the minute and second hands  1 ,  2  run above it, the hour display, however, below it. Instead of the guide pin  21  the gear wheel E then bears an especially prominent marking, owing to its brightness or colour—for instance a round small disc—which runs around the-two-loop curve  31 . This small disc then replaces the point of the hour hand  5 . The latter and also the aforesaid small disc are then indicating elements. 
     For the gearing specialist other arrangements of gear wheels and possibly the arms carrying them, can be realised and are included in the inventive idea, which fulfill the aim of generating the desired conchoid as a track for the indicating, element, using a guide pin  21  or a corresponding component.