Abstract:
The invention relates to a drive system for a scanning device of an information recording or reproduction device, with a carriage coupled to a toothed rack, a gear wheel mechanism driving the toothed rack and a gear housing. It achieves the object of designing a drive system of this type alternatively and in such a way that it ensures a high speed and positioning accuracy of the carriage. For this purpose, the gear wheel mechanism is secured on a supporting element and the gear housing, the gear housing consisting of a dimensionally stable material and being pivotable with the gear wheel mechanism about a spindle which is arranged perpendicularly with respect to the toothed rack.

Description:
FIELD OF THE INVENTION 
   The invention relates to a drive system for a scanning device of an information recording or reproduction device, in which the scanning device reads or stores information or data in one or more tracks of a recording carrier. The recording carrier may in this case be a compact disc, known as a CD, a digital versatile disc, known as a DVD, a CD ROM or DVD ROM or a re-writable CD or DVD, or else a magnetooptical or other recording carrier. 
   BACKGROUND OF THE INVENTION 
   Devices for recording or reproducing information or data in one or more tracks of a recording carrier which are provided with a scanning device for reading or recording information, referred to as a “pickup”, are generally known. The respective scanning device is usually arranged on a carriage which can move obliquely or perpendicularly with respect to the recording track. To achieve a high speed and positioning accuracy, combined with a short access time to different locations of the recording carrier, this carriage is coupled to a toothed rack, which is driven by an electric motor via a gear mechanism. The output shaft of the electric motor is provided for this purpose with a pinion or with a worm wheel, which is in engagement with the gear mechanism. In order to prevent positional changes of the carriage, and consequently of the scanning device, when the drive is switched off or the electric motor is switched off, the gear mechanism is of a self-locking type of design. To meet the requirement for high positioning accuracy and short access time, a gear mechanism with a high transmission ratio is used. The toothed rack arrangement and the gear wheel driving the toothed rack are preferably formed with straight teeth, in order to avoid deflections of the scanning device in the direction of the recording carrier, such as the focusing direction in the case of an optical recording carrier, during tracking or track skipping and when reversing the driving direction. 
   To reduce gear noises and to improve the tracking behavior of the gear mechanism, small gear modules are preferred, the gear elements of which must have high precision and the production of which requires great care. Generally, gear mechanisms are also greased, in order to avoid running noises. However, the use of lubricating grease for noise reduction entails the risk of the other components of the scanning device, especially the optical components, being soiled by the lubricating grease, whereby the functional capability of the scanning device is impaired. Therefore, the respective gear mechanism is usually accommodated in a housing, which may at the same time advantageously bring about a further reduction in noise. 
   It is further known to use a flexible toothed rack or else an additional toothed rack on the scanning device side to minimize gear play. Similarly it is known to use coupling systems or flexible gear shafts or spindles or else flexible gear housings on the drive side, in order to protect the gear mechanism from mechanical damage. However, flexible gear shafts and/or flexible gear housings are problematical with regard to the accuracy of the system, because the gear wheel engagement is not optimal under normal circumstances and a flexible gear shaft or gear wheel shaft may bend under operational loading, to the detriment of accuracy. Additional elements in the drive system for the scanning device increase the diversity of the components, the care required and the effort involved in the assembly process, and consequently the production costs. 
   SUMMARY OF THE INVENTION 
   It is therefore an aspect of the invention to design the drive system for a scanning device of an information recording or reproduction device according to the preamble of claim  1  alternatively in such a way that it ensures a high speed and positioning accuracy of the carriage along with low noise development and simple assembly. 
   This is achieved in the case of a drive system according to the preamble of claim  1  by the defining features of the latter. Advantageous refinements are presented in the subclaims. 
   The invention consists in that the gear wheel mechanism of a drive system for a scanning device of an information recording or reproduction device which is in engagement with a toothed rack coupled to a carriage is secured on a supporting element and a dimensionally stable gear housing. In this case, the gear housing is pivotable to a predetermined degree together with the gear wheel mechanism about a spindle which is arranged perpendicular to the toothed rack and parallel to the gear spindles. The latter are likewise produced from a solid material and are not flexible. The arrangement and design of the gear housing, in particular of the pivoting spindle, make it possible for said housing to be pivoted together with the gear wheel mechanism as a whole against the toothed rack during the operation of the drive device and always kept in an exact and fixed engagement with the latter, in particular even when there is a reversal of the direction of movement of the drive system. The engagement optimized in this way has the effect of compensating for the play of the gear wheel or of the gear mechanism with respect to the toothed rack, which in turn increases the positioning accuracy of the carriage. The pressure which is thereby exerted on the gear wheel in engagement with the toothed rack, and its shaft or spindle, is also reduced. Furthermore, exact engagement, and the associated optimized running of the gear system, reduces running noises. 
   The gear housing is formed in such a way that it partly encloses and covers the gear wheel on the toothed rack side, so that undesired impairments of further components of the scanning device associated with lubrication of the gear mechanism are avoided. The drive system can be assembled in a reliable process. Production tolerances are also compensated, so that the risk of damage to the gear mechanism during normal operation is essentially ruled out. 
   In order that the shaft or spindle of the gear wheel on the toothed rack side can perform a movement corresponding to a pivoting movement of the gear housing, a guiding slot in which the end region of the gear wheel shaft on the supporting element side engages is formed in the supporting element. This guiding slot has a curvature with a radius which corresponds to the distance from the spindle of the gear wheel shaft to the pivoting spindle of the gear housing. 
   Positioning of the gear housing, and consequently also of the gear mechanism, with respect to the toothed rack is made possible by means of a resilient arm which is formed on the gear housing and, at a distance from the latter, engages in a clearance which is formed in the supporting element and provided with a detent. The detent fixes the arm in a defined position. While the drive device is not in operation, the arm is relaxed. 
   During operation, the gear mechanism is acted on by a drive torque. As a result, the gear mechanism and the gear housing coupled to it are pivoted about the pivoting spindle, so that the arm fixed by its free end in the supporting element is also pivoted along with it and prestressed as a result. This prestressing in turn causes a torque on the drive housing and the gear mechanism in such a way that the gear wheel on the toothed rack side is pressed against the toothed rack. As a result, an integral toothed rack can be used in an advantageous way. 
   In a preferred embodiment, the gear housing is connected to the supporting element via connecting means similar to bayonet fasteners. These are arranged and formed in such a way that their closing position, in which the gear housing is connected to the supporting element, is obtained when the arm is in its relaxed position—its position without any prestress. In this case, the connecting means are formed in such a way that they permit a pivoting movement of the gear housing within the predetermined limits without the gear housing being detached from the supporting element. The gear mechanism is self-locking and nevertheless the gear mechanism is protected from mechanical damage by the pivoting movement. The connecting means similar to bayonet fasteners permit considerably easier assembly. 
   In a preferred embodiment, the gear mechanism is formed by a number of gear wheels, and the pivoting spindle is at the same time the spindle of an intermediate gear wheel included as part of the gear mechanism. The gear wheels may be produced from a flexible plastic and the spindles of the gear wheels are formed by webs of the gear housing. 

   
     BRIEF DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention is explained below in drawings on the basis of an exemplary embodiment. In the associated drawings: 
       FIG. 1  shows a plan view of a scanning device, 
       FIG. 2  shows an exploded representation of the gear wheel mechanism coupled to a gear housing, 
       FIG. 3  shows a plan view of this, enlarged, and 
       FIG. 4  shows a bayonet hook in engagement with a supporting plate, greatly enlarged. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The scanning device  1  represented in  FIG. 1  is arranged on a supporting plate  2  and coupled to a drive system formed by an electric motor  3 , a gear wheel mechanism  4  and a toothed rack  5  in engagement with the latter, the toothed rack  5  being integrally formed and securely connected to a carriage  7  guided on guiding rods  6 . The carriage  7  bears the scanning device  1 , which is intended for the scanning of optical recording carriers. It has an objective lens  8 , which is used for focusing a light beam or laser beam for recording or playing back information or data on a recording carrier (not shown), which is detachably arranged on a turntable  9  by which the recording carrier is set in rotation. The gear wheel mechanism  4  is formed by two straight-toothed gear wheels  10  and  11 , which are coupled to a gear housing  12  made of a dimensionally stable plastic, such as for example polypropylene. Integrally formed on the gear housing  12  are an arm  13 , which is resilient due to the choice of the plastic, and also three bayonet hooks  14 , which engage at clearances  15 ,  16  arranged in the supporting plate  2  and corresponding to them, the bayonet hooks  14  engaging behind the supporting plate  2  in the region of the clearances  15  in the connection position. The connection position is provided by the arm  13  engaging in the supporting plate  2  at a distance from the gear housing  12  and being relaxed. For the assembly of the gear housing  12 , this arm  13  is easily pushed away to the side, in such a way that it is possible both for the latter to be pushed into the clearance  16  and for the bayonet hooks  14  to be pushed through the clearances  15 . By removing the pressure from the arm  13 , the latter relaxes as a result of its resilient property and turns the gear housing  12 , and consequently also the bayonet hooks  14 , so that the angled-away ends of the latter go under the supporting plate  2 . 
   As an alternative to the embodiment described above, the bayonet hooks  14  may be provided, according to  FIG. 4 , with a snap projection  26 , which is directed radially with respect to the spindle  21  and brings about the assembly-facilitating effect that it engages with the supporting plate or snaps into it already after it has been pushed through the clearance  15 , without turning into the connection position taking place. The snap projection represents an additional securement for the connection arrangement between the supporting plate  2 , the gear wheel mechanism  4  and the gear housing  12 . 
     FIG. 2  shows the arrangement and formation of the gear wheel housing  4  and of the gear housing  12  coupled to the latter. The two straight-toothed gear wheels  10  and  11  are in engagement with each other via a pinion  17 , arranged on the gear wheel  10  on the electric motor side, the gear wheel  10  is in engagement with the electric motor  3  via a pinion  18  arranged on the output shaft of the latter and the gear wheel  11  on the toothed rack side is in engagement with the toothed rack  5 , not represented in this figure, via a pinion  19  arranged on it. In this case, the output shaft of the electric motor  3  protrudes with the pinion  18  through an opening  20  arranged in the supporting plate  2 , from the underside to the upper side of the same, on which the gear wheels  10  and  11  and the gear housing  12  are secured. 
   Arranged on the gear housing  12  are two spindles  21  and  22  for the gear wheels  10  and  11 , which in the assembly position of the gear housing  12  are aligned perpendicularly with respect to the toothed rack  5 . The spindle  21  thereby engages with its free end fixedly into a bore  23  formed in the supporting plate  2 , and the spindle  22  receiving the gear wheel  11  on the toothed rack side engages in a curved long-hole guide  24 , which has a radius of curvature which corresponds to the distance of the two spindles  21  and  22  from each other. The long-hole guide  24  permits a pivoting movement of the gear housing  12  and consequently of the spindle  22  and of the gear wheel  11  about the fixed spindle  21  and at the same time limits this movement by its length. In this case, the spindle  21  is at the same time the axis of rotation of the gear wheel  10 . 
     FIG. 2  also clearly shows the bayonet hooks  14  formed on the gear housing  12  and the clearances  15  provided for them in the supporting plate  2 . Also represented are the arm  13  and the clearance  16  provided for it. Formed in the latter is a detent  25 , by which the arm  13  is fixed in a defined engagement position. This corresponds on the unactuated gear wheel mechanism  4  to the closed position of the bayonet hooks  14  and a relaxed arm  13 . The gear housing  12  and the gear wheels  10  and  11  can only be disassembled by detaching the arm  13  from the clearance  16  while overcoming the detent  25 . In  FIG. 3 , the gear wheel—and gear housing arrangement—are illustrated in an enlarged representation. 
   The drive system is assembled by firstly screwing the electric motor  3  in its predetermined position onto the underside of the supporting plate  2 , whereby it protrudes through the supporting plate  2  with the pinion  18  arranged on its output shaft. Subsequently, the two gear wheels  10  and  11  are pushed onto the spindles  21  and  22  in the gear housing  12  and pre-assembled in this way, the pinion  17  arranged on the gear wheel  10  coming into engagement with the gear wheel  11 . After that, this preassembly unit is mounted in a simple way onto the supporting plate  2 , by the bayonet hooks  14  and the free end of the arm  13  being inserted into the clearances  15  and  16  provided for them, the arm  13  or its free end having to be pressed to the side and stressed, in order to be able to snap into the clearance  16 . As this happens, the pinion  18  comes into engagement with the gear wheel  10  and the pinion  19  comes into engagement with the toothed rack  5 . The gear housing  12  is firmly pressed onto the supporting plate, whereby the angled portions of the bayonet hooks  14  go under the supporting plate  2  and, when the arm  13  is relaxed, are turned into their closed position, in which they can slide on the supporting plate  2  within the limits of the extent of the long-hole guide  24  for the spindle  22 . Disassembly of the drive system takes place in a simple way, by the gear housing  12  being turned into the insertion position for the bayonet hooks  14  in the clearances  15  and pulled away from the supporting plate  2 , so that the bayonet hooks  14  and the free end of the arm  13  disengage from the clearances  15  and  16 . 
   The gear wheel  11 , which is pivotable about the spindle  21  within the limits of the extent of the long-hole guide  24 , is in an exact and fixed engagement with the toothed rack  5 , the gear housing  12  with the spindle  21  being prepositioned by the arm  13 . A change in the direction of rotation of the gear wheel mechanism caused by a controlled reversal of the drive direction of the electric motor  3 , associated with a reversal of the torque, is taken up by the gear housing  12 , which is pivotable about the spindle  21 , and the prestressable arm  13 , and play occurring between the gear wheel  11  and the toothed rack  5  is compensated. The gear wheel  11  on the toothed rack side is pressed against the toothed rack  5  independently of the direction of rotation of the electric motor  3 , so that, by contrast with toothed racks complexly braced against one another, an integral toothed rack  5  is used and can be used. On the other hand, the gear mechanism is protected from mechanical damage by the resiliently supported pivotability of the gear housing  12 . The gear housing  12 , fastened onto the supporting plate  2  by bayonet hooks  14 , has webs which advantageously form the spindles  21  and  22  of the gear wheels  10  and  11  and the gear housing  12  further serves both for noise reduction and for protection of the surroundings from influences of the gear mechanism, if for example it has lubricants. 
   LIST OF DESIGNATIONS 
   
       
         1  scanning device 
         2  supporting plate 
         3  electric motor 
         4  gear wheel mechanism 
         5  toothed rack 
         6  guiding rod 
         7  carriage 
         8  objective lens 
         9  turntable 
         10  gear wheel 
         11  gear wheel 
         12  gear housing 
         13  arm 
         14  bayonet hook 
         15  clearance 
         16  clearance 
         17  pinion 
         18  pinion 
         19  pinion 
         20  opening 
         21  spindle 
         22  spindle 
         23  bore 
         24  long-hole guide 
         25  detent 
         26  snap projection