Abstract:
Transport device for work-pieces or the like, which are set upon plate or pallet-shaped work-piece carriers, with a support device, upon which the work-piece carrier is translationally displaceably seated, and a drive device, which is continuously driveable by a drive motor and in frictional contact with the work-piece carrier is brought, wherein the support device is comprised of plurality of sequentially arranged support rollers ( 26 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention concerns a transport device for work-pieces or the like. 
     2. Description of the Related Art 
     This type of device is generally well known and is employed in industries with substantially automated processes. 
     These known transport devices include plate or pallet-shaped work-piece carriers, upon which the material to be transported is deposited. The work-piece carriers are seated upon two drive belts running parallel to each other in the form of belt bands, which for their part are supported upon slide rails. The two belt bands are driven to rotate by a drive motor and thereby take along the work-piece carrier seated thereupon. It is thus necessary that the work-piece carrier frictionally engage the belt bands. 
     The problem in this regard is the contact occurring between the belt bands and the slide rails, since as a consequence of the high weight of the work-pieces inclusive of the work-pieces carried thereon, a high friction force occurs. This problem is enhanced in the case of a traffic jam of work-piece carriers, which occurs regularly, for example when work-pieces arrive at specific work stations for processing and thus the associated work-piece carriers are stopped. Thereby supplemental frictional forces occur between the belt and the stopped work-piece carrier. 
     As a consequence of this effect, high drive forces are required in order to ensure operation of the device. Nevertheless, there is a great danger, that in the case of an overload of the conveyor belts the drive motor becomes damaged. There is a further problem in that in the case of continued driving under a high loading a strong fouling occurs. Even if the glide rails are made of stainless steel with a stamped or indented upper surface, this cannot satisfactorily solve the above-mentioned problem. Finally, it can occur in the case of large volume work-pieces, that on the basis of the their larger area, the surface of the work-piece carrier does not have sufficient friction engaging contact and thus can slide on the conveyor belt. 
     The present invention is thus concerned with the task, of improving a transport device of the above-mentioned type in such a manner, that the above-mentioned disadvantages no longer occur. In particular, a reliable transport of work-piece carriers should be achieved under all operating conditions, without causing an overload of the drive motor. 
     SUMMARY OF THE INVENTION 
     The invention is based upon the idea, of providing the work-piece carrier upon support rollers, and in this manner to replace the conventional sliding friction, which occurs during transport of the work-piece carrier, with roller friction. Thereby the capacity of the drive means needed to operate the device is substantially reduced. In the case of a continuous operation, this results in a substantial savings and energy costs. Practical tests have found that a savings potential of up to 90% can be achieved. 
     Preferably two rows of support rollers are provided parallel to each other, wherein the spacing of the two rows is set to correspond to the (standardized) breadth of the workpiece carrier. 
     Preferably side guides are provided, between which the work-piece carrier is guided with close sideways tolerance. The close tolerance prevents a tipping of the work-piece carrier during the transport movement. 
     Further variants are concerned with optimizing the design of the drive device. 
     A first variant envisions the use of a conventional drive belt. As a result of the substantially reduced drive requirement, it is in most cases sufficient to employ a single drive belt, which frictionally engages with the work-piece carriers in the translation direction in a conventional manner. 
     It has been found to be particularly advantageous when, for the production of the press force necessary for frictional engagement, a multiplicity of sequential, individual slide bars are provided which act upon the drive belt via a spring or biasing device. As a consequence of the spring device, the drive belt is raised slightly, for example 1 to 5 mm. When a work-piece carrier passes over, the respective glide bar is pressed downwards by the weight of the work-piece carrier inclusive of the thereupon situated work-piece, producing a press force which ensures the frictional engagement between the drive belt and the work-piece carrier necessary for the transport. In this manner, the glide bar bars are loaded sequentially one after the other or, as the case may be, in groups, by the work-piece carrier being guided over them. In the case of a traffic jam, the drive belt continues to move below the stopped work-piece carriers. On the basis of the substantially reduced press force, there is, however, no danger of overheating of the drive motor. Also, overall the wear due to friction of the drive is substantially reduced. As a supplemental side effect, it has been determined that the noise level of the overall installation is very much reduced in comparison to the state of the art transport devices. 
     Preferably, each glide bar is individually spring biased. This makes possible an optimal loading of the drive belt, since the glide pieces are deflected by the work-piece carrier passing over without any reciprocal change-out action. 
     In a sense of a kinematic reverse, it is likewise possible to run the drive belt over a fixed—that is—not spring biased glide rail and in its place to provide on the work-piece carrier a spring-biased take-along rail, which ensures a defined pressure force for production of the frictional engagement with the drive belt. In this variant also, each work-piece carrier is supported via support rolls. 
     In a further variant the support rollers are spring-biased. Herein the spring characteristics are so determined, that the main load of the respective impacted support rollers is taken over and a pre-determined residual loading remains for production of the friction-locking contact to the non-yielding or unbiased drive belt. 
     It is understood that, on the basis of the above-described concept, transport devices can be run in any of various lengths. It can, however, be of advantage, to divide the drive unit into multiple, sequentially arranged, sectional drives, since if the drive belt is too long it must be tensioned too tightly. 
     A last variant is concerned therewith, to completely dispense with a drive belt in the design of the drive device and instead of this to employ a friction roller drive. Herein at certain separations or distances friction rollers are provided, this being between the support rollers. In this case it must also be ensured, using a spring device, that the friction rollers are pressed against the respective work-piece carriers, in order to produce a friction-locking contact. 
     According to an inventive concept, so-called “translators” can be constructed, with the help of which, using conventional means and manner, work-piece carriers can be removed perpendicularly to the transport direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     On the basis of the illustrative embodiment shown schematically in the drawing, the invention, advantageous embodiments, and improvements of the invention as well as particular advantages of the invention shall be discussed and described. 
     There is shown in: 
     FIG. 1 a diagonal view of a known transport device; 
     FIG. 2 a diagonal view of a transport device according to the invention; 
     FIG. 3 a cross-section through the transport device according to FIG. 2; 
     FIG. 4 a cross-section through a first variant of the transport device; and 
     FIG. 5 a side view of a second variant of the transport device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1 a conventional transport device  10  corresponding to the state of the art is shown in diagonal view. It includes two drive belts  12  arranged parallel to each other, which are acted upon by a motor  13  and of which the upper running segment is respectively supported by a support rail. A work-piece carrier  16  resting upon the drive belt  12  presses the drive belt against the support rails  41  and produces thereby the friction locking contact necessary for the translational displacement with the drive belt  12 . Side guides  18  arranged longitudinal along the sides direct the work-piece carrier  16  and ensure, that it is continuously centered on the transport device  10 . 
     The support rails, here not shown in detail, a stamped or indented upper surface, over which the drive belt  12  slides or guides. The stampings or indentations ensure for a reduced frictional rubbing of the drive belt  12  against the support rails. 
     In FIG. 2 an inventive transport device  20  is shown likewise in diagonal representation. Here also the transport movement occurs via a drive motor  21  acting on—in this case, one—drive belt  22 , of which the upper segment likewise is supported. 
     A substantial departure from the state of the art is comprised therein that, while the work-piece carrier  16  to be transported may work in cooperation with a drive belt  22 , its mass however is respectively taken up by support rollers  26  provided along both longitudinal sides, which take up the weight resting thereon. 
     The support rollers  26  are provided or arranged in a very close proximity a to each other, for example a ≦3/2 R with R=Radius support roll , so that surface pressing is minimized. The support rollers  26  are preferably provided with a (here not shown in greater detail) roller bearing, for example, pin bearings, ball bearings, or needle bearings, whereby a very low rolling resistance is achieved and therewith a comparatively small drive force is required for transport of the work-piece  16 . As a result, the capacity of the drive motor  21  can be reduced by at least one-half in comparison to those used in the state of the art. 
     A further departure from the state of the art is that in the inventive transport device  20 , in the place of two continuous one-piece support tracks, a multitude of individual, longitudinally aligned, sequentially arranged glide bars  24  are provided. 
     The glide bars  24  are respectively provided with a spring means  23 , which is here indicated only symbolically and in FIG. 3 is shown in greater detail. 
     In FIG. 3 a cross-section through the drive side of the  10  transport device is shown. A glide bar  24  with L-shaped cross section is guided into a box profile  30  and urged upwardly against the drive belt  22  via a helical pressure spring  33  in the direction of arrow F. 
     The glide bar  24  has, on its surface contacting the drive belt  22 , a glide strip  25  of finely imprinted or indented stainless steel, which has particularly suitable gliding characteristics, that is, as a consequence of its low frictional value has a low gliding or sliding resistance. 
     The glide bar  24  has on its sides a side guide  28  directed  20  against the work-piece carrier  16  in the manner of an abutment glide bar. 
     In the inner side of the box profile  30 , supports  36  for respectively one support roller  26  are secured. The supports  36  are height-adjustable, so that an optimal support height for the work-piece carrier  16  can be set for achievement of the pressure force exercised by the glide bars  24  on the drive belt  12 . 
     In FIG. 4 a variant of the inventive transport device  20  is shown. 
     Departing from the variant shown in FIG. 3, here the glide  30  bar  24  is provided stationary on the box profile  30 , wherein the pressure force is produced by a spring device  33  integrated in the work-piece carrier  16  and transmitted to the drive belt  22  via a take-along bar  32 . The further characteristics correspond to the design shown in FIG.  3 . 
     In FIG. 5 a side view of an alternative drive concept for the transport device  40  according to the invention is shown with friction rollers  27  acting upon the work-piece carrier  16 . 
     In the place of a drive belt, friction rollers  27  are provided spaced apart from each other, which are provided between the support rollers  26 , wherein in the shown example respectively two support rollers are situated between two drive rollers. The friction rollers  27  are spring mounted as discussed above, so that also here an optimal press-force for achievement of a friction locking is produced, in order to transport the work-piece carrier. 
     From the preceding description there can be seen as a common fundamental concept that the work-piece carriers  16  are supported so as to be easily transportable as a consequence of the support provided by the support-rollers  16 , as a result of which, for a transport movement from stationary, essentially only the roller friction must be overcome. For the drive means a comparatively small capacity drive unit will suffice, in order to overcome the mass moment of inertia of the work-piece carrier inclusive of the thereupon placed work-pieces. Insofar as belts continue to be used for the drive, the friction rubbing is limited to a comparatively small amount. 
     In accordance with the inventive concept, it is possible not only to design conveyors for conventional transport devices. It is possible, beyond this, to also design translators. 
     REFERENCE NUMBERS LIST 
       10  Transport device (state of the art) 
       12  Drive belt 
       13  Drive motor 
       14  Carrier glide track (glide bar) 
       16  Work-piece carrier 
       18  Side guide 
       20  Transport device (inventive) 
       21  Drive motor 
       22  Drive belt 
       23  Spring device 
       24  Glide bar 
       25  Glide track 
       26  Support roller 
       27  Friction roller 
       28  Longitudinal guide 
       30  Box profile 
       32  Take-along bar 
       33  Spring device 
       36  Support 
       40  Alternative transport device (inventive) 
       44  Transport device