Abstract:
The subject matter of the invention is a continuous through-feed grinding machine for machining a workpiece surface, said grinding machine having a grinding station with at least two rotating grinding tools, more specifically disc or roll grinders, with the grinding tools being continuously advanced along an endless path. The objective of providing a continuous through-feed grinding machine allowing for even machining of the workpiece surface with even wear of the grinding tools is accomplished by providing the endless path ( 128 ) with two work segments ( 140, 142 ) alternating with two transfer segments ( 144, 146 ) or by continuously advancing grinding tools that are moved along an endless path configured as an oval or elliptical shape.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims Priority from German Application No. DE 203 19 366.0 filed on 13, Dec. 2003.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a continuous through-feed grinding machine and method for machining a workpiece surface, said grinding machine having a grinding station with at least two rotating grinding tools, more specifically disc grinders or rolls.  
         [0004]     The manufacturing of pieces of furniture, room doors or the like requires surface grinding of the various components after machining in order to remove possible burs and/or to smooth the surface and to eliminate therefrom fine wood fibers. Only if the surface is thus made smooth can it be varnished properly. This applies in equivalent fashion to pre-varnished workpieces. Further, continuous through-feed grinding machines are utilized for deburring metal workpieces.  
         [0005]     Especially if actually plane surfaces comprise raised portions, depressions or recesses, discrete workpieces are transported on a conveyor system along one or several grinding stations in such type continuous through-feed grinding machines, said grinding stations being provided with abrasive discs and/or rolls to which abrasive paper is mounted in a lamellar fashion. The abrasive discs or rolls thereby machine the workpiece, more specifically the profile thereof, from different angles in order to break possible edges and/or to remove burs.  
         [0006]     2. Description of the Prior Art  
         [0007]     From DE 100 35 977A1 for example it is known to integrate into a continuous through-feed grinding machine both an abrasive flap roll leading over the entire width of the workpiece and a number of abrasive flap discs (also known as “disc grinders”). Thereby, the abrasive flap roll is intended to grind the surface of the workpiece in the direction of transport, while the disc grinders rotate about their vertical axis, thus machining the surface of the workpiece from different directions. The disc grinders are not only rotated, they are also moved in an oscillating manner across the infeed direction so as to machine every point of the workpiece surface from different angles.  
         [0008]     A grinding station for a continuous through-feed grinding machine is known from DE 196 11 932 A1 in which four secondary rotation axes are provided on one primary rotation axis, four roll grinders being mounted to each secondary rotation axis. The roll grinders thereby rotate about their horizontal axis and both the primary and the secondary rotation axes cause the roll grinder to rotate once more. As a result, the respective one of the roll grinders is caused to move diffusely across the surface of the workpiece, the objective being to grind each point of the workpiece surface as far as practicable from different angles in order to make it possible to sufficiently grind even complex edges, profiles or other patterns.  
         [0009]     A grinding station is known from WO 99/22905 in which a number of roll grinders is mounted to a vertical axis, the roll grinders rotating about their horizontal axis on the one side and about the vertical axis on the other side.  
         [0010]     In all the continuous through-feed grinding machines mentioned herein above, the surface of the workpiece is ground by the various grinding tools from different directions and angles. Actually, the surface of the workpiece is not machined uniformly thereby. Accordingly, there are regions of the workpiece surface that are mainly contacted at a certain angle or that are machined at a high or a low relative velocity, which leads to different grinding results and to different wear of the grinding tool. The oscillating movement across the direction of transport, combined with the rotation of the grinding tool and the movement of the workpiece, causes the grinding tool to move relative to the surface of the workpiece in a manner that is locally very irregular. Additionally, this causes the various grinding tools to wear unevenly if the workpiece to be machined does not extend over the entire machining width but only covers a portion of said width. Such unevenly worn grinding tools however compromise the grinding results of subsequent workpiece surfaces since different grinding results within the workpiece are obtained due to differing wear.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011]     In view thereof, it is the object of the present invention to provide a continuous through-feed grinding machine of the type mentioned herein above that permits to achieve even machining of the workpiece surface and even wear of the grinding tools.  
         [0012]     As a technical approach to achieve this object, the invention proposes a continuous through-feed grinding machine according to the features of claim  1  or the features of claim  5 . Advantageous developed implementations of this continuous through-feed grinding machine will become apparent from the subordinate claims.  
         [0013]     A continuous through-feed grinding machine formed in accordance with this technical teaching has the advantage that the endless path permits to achieve a defined movement of the grinding tools over the workpiece surface, said grinding tools being at all times evenly guided over the surface of the workpiece so that even machining of the workpiece surface and even wear of the grinding tools are achieved.  
         [0014]     Another advantage is that this defined movement may be used by the machine upsetter to place the various workpieces on the conveyor in accordance with their profile in such a manner that they are optimally contacted with the grinding tools, thus ensuring thorough grinding.  
         [0015]     In a preferred embodiment, the endless path is dimensioned such that only a portion of the endless path is located in the region of the expected workpiece surface whilst another portion of the endless path is disposed outside of the workpiece surface. The endless path is advantageously configured in such a manner that those segments of the endless path in which the grinding tools are moved linearly or almost linearly are disposed above the expected workpiece surface, more specifically above the conveyor, whilst those portions of the endless path that are sharply curved or in which the workpieces are merely transferred are disposed outside of the expected workpiece surface. As a result thereof, the grinding tools are moved exclusively or almost linearly over the workpiece surface. It may thereby be left open whether the grinding tools are moved along the direction of transport of the workpieces or across thereto or at an angle of between +45° and −45° to the direction of transport. In any case, uniform movement of the grinding tools is achieved through the linear movement in the region of the grinding process.  
         [0016]     This offers the advantage that the relative velocity of the tools relative to the workpiece surface is always the same so that even grinding is achieved. Another advantage is that this even grinding also results in even wear of the grinding tools, which on the one side enhances the quality of the grinding result and on the other side leads to a more profitable utilization with the capacity of the grinding tools being better utilized.  
         [0017]     In a preferred embodiment the grinding station includes a guide rail configured to conform to the endless path and on which a number of carriages are guided, each carriage in turn holding one grinding tool. This has the advantage that the grinding tools can be reliably guided at lower cost. The utilization of a guide rail-carriage combination also allows for a low-friction, failure free movement of the grinding tools.  
         [0018]     It has been found advantageous to connect via a tie rod said carriages to a positively driven chain so that a chain that is driven by an electric motor pulls the carriage.  
         [0019]     In a particularly preferred developed implementation, a gear rim is held on the guide rail, said gear rim cooperating with a gearwheel mounted to the grinding tool so that the grinding tool rotates about its vertical axis as long as the carriage is moved forward. The rpm of the grinding tools is thereby coupled to the revolving velocity of the grinding tools along the endless path. This permits to achieve at low cost rotation of the grinding tool about its vertical axis so that the grinding tool does not grind the workpiece surface in a direction across the direction of transport only but also performs grinding at any other angle as a result of its motion of rotation. By thus indirectly driving the grinding tools, the entire grinding station can be driven with but one drive motor, which again reduces the cost of manufacturing.  
         [0020]     In an alternative embodiment, each grinding tool is driven by its own electric motor. This has the advantage that the rpm of the grinding tools may be adjusted independently of the speed of the carriages revolving on the endless path. The grinding tools may likewise be operated at much higher speed. As a result, it is possible to machine both wood or wood substitutes (low rpm) and metal (high rpm) using but one continuous through-feed grinding machine. This widens the range of applications and, as a result thereof, increases the profitability of the continuous through-feed grinding machine of the invention.  
         [0021]     Another advantage is that, as a result of the higher rpm of the grinding tools, the entire grinding process is completed sooner, which increases the throughput.  
         [0022]     In a preferred embodiment, the grinding tools are individually controllable. This has the advantage that, depending on the required grinding conditions, the grinding tools may be connected on or off or their speed may be adjusted or they may be operated in the desired direction of rotation, which makes it possible to optimally adjust the grinding process to the requirements of the workpiece.  
         [0023]     In another preferred embodiment, the grinding station is equipped with disc grinders only since these offer advantages in the multi-sided machining of workpieces.  
         [0024]     In another preferred embodiment, the grinding station is equipped with roll grinders only since these allow for more aggressive machining. Such type machining is particularly advantageous for deburring metal pieces.  
         [0025]     In still another preferred embodiment, the grinding station is provided with both disc grinders and roll grinders. The roll grinders may thereby be disposed with their rotation axis in the infeed direction, across the infeed direction or at any angle, more specifically at an angle of 45°, to the infeed direction. This has the advantage that the grinding station may be adapted to the workpieces to be ground in order to achieve the best possible grinding result with, as far as possible, even wear of the grinding tools.  
         [0026]     Another advantage is that a desired grinding pattern can be achieved by individually arranging the grinding tools. This grinding pattern may thereby be oriented in the direction of the set angle of the angle grinder but may also be diffuse if different grinding tools are being utilized or if the grinding tools are differently aligned.  
         [0027]     In a most preferred embodiment, the grinding station is equipped with three identical groups of grinding tools, each group of grinding tools including one disc grinder, one roll grinder mounted in the infeed direction, one mounted across the infeed direction and one inclined at an angle of 45° to the infeed direction. As a result, the depressions and raised portions as well as the borders and edges of the workpiece are ground from many different sides so that the workpiece is thoroughly machined.  
         [0028]     Another advantage is that while the workpiece is so thoroughly and completely machined the transport speed of the workpiece may be increased without compromising the machining quality. This increased speed results in greater throughput and in greater profitability of the continuous through-feed grinding machine of the invention.  
         [0029]     Further advantages of the continuous through-feed grinding machine of the invention will become apparent in the appended drawings and in the following description of embodiments thereof. Likewise, the above mentioned features and those described herein after may be used alone or in any combination with each other within the scope of the present invention. The embodiments discussed herein are merely exemplary in nature and are not intended to limit the scope of the invention in any manner. 
     
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING  
       [0030]     In the drawings:  
         [0031]      FIG. 1  is a top view of a first embodiment of a grinding station of a continuous through-feed grinding machine of the invention;  
         [0032]      FIG. 2  is a front view of the grinding station of  FIG. 1 ;  
         [0033]      FIG. 3  is a front view of an enlarged detail of a part of the grinding station of  FIG. 2  taken along line III of  FIG. 2 ;  
         [0034]      FIG. 4  is an enlarged detail of a part of a second embodiment of a grinding station of a continuous through-feed grinding machine of the invention;  
         [0035]      FIG. 5  is a top view of a third embodiment of a grinding station of a continuous through-feed grinding machine of the invention;  
         [0036]      FIG. 6  is a front view of an enlarged detail of a part of the grinding station of  FIG. 5 ;  
         [0037]      FIG. 7  is a top view of the continuous through-feed grinding machine of  FIG. 5 , but with obliquely mounted roll grinders;  
         [0038]      FIG. 8  is a top view of the continuous through-feed grinding machine of  FIG. 5 , but with crosswise mounted roll grinders;  
         [0039]      FIG. 9  is a top view of the continuous through-feed grinding machine of  FIG. 5 , but with both obliquely and crosswise mounted roll grinders;  
         [0040]      FIG. 10  is a top view of a fourth embodiment of a grinding station of a continuous through-feed grinding machine of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]     The  FIGS. 1 through 3  illustrate a first continuous through-feed grinding machine in which workpieces  112  having a plane workpiece surface are conducted on a conveyor  110  past a grinding station  114 . Generally, the workpieces  112  are doors, boards or other furniture components or the like made of wood or wood substitute, with the substantially plane or profiled surfaces being uniformly ground, polished or roughened. After the surface of these workpieces  112  has been mechanically machined, it must be ground in order to remove burs and protruding wood fibers and to smooth the surface. Depressions and raised portions such as for example milling cuts, mounted ledges or the like which are oriented across or along the infeed direction or at any angle thereto should thereby also be ground uniformly as far as practicable. The workpieces may be metal parts comprising milling cuts, holes, openings or recesses.  
         [0042]     The grinding station  114  includes an electric drive  116  and a return pulley  118 , an endless moving chain  120  being guided about the electric drive  116  and the return pulley  118 . Said chain  120  pulls a number of grinding tools which, in the embodiment illustrated herein, are configured to be disc grinders  122 . On its side turned towards the workpiece, each disc grinder  122  is equipped with a number of grinding lamellae and on the side turned toward the grinding station, the grinding tool  122  comprises a vertical axis.  124 . The disc grinder  122  is retained at its vertical axis  124  on a travellable carriage  126  and can be caused to move along an endless path  128  by the carriage  126 . The endless path  128  is implemented as a guide rail  130  that retains the respective one of the carriages  126  and slidably guides them along the endless path  128 . The carriage  126  is connected to the chain  120  through a tie rod  132 , said tie rod  132  being pivotally carried both on the chain  120  and on the carriage  126 .  
         [0043]     A gearwheel  134  that meshes with a gear rim  136  mounted to the inner side of the guide rail  130  is mounted to the vertical axis  124 . This gear rim  136 -gearwheel  134 -combination causes the grinding tool  122  to rotate about its vertical axis  124  as soon as the disc grinder  122  is advanced. This construction makes it possible to readily move the grinding tools  122  along the endless path  128  using but one single electric drive  116 .  
         [0044]     The endless path  128  is composed of four segments, namely a first work segment  140 , a second work segment  142 , a first transfer segment  144  and a second transfer segment  146 . Like the two transfer segments  144 ,  146 , the two work segments  140 ,  142  are oppositely disposed from each other. The actual grinding process only occurs in the work segments  140  and  142  which are located above the expected workpiece surface. The work segments  140  and  142  thereby extend over the entire width of the conveyor  110 . The transfer segments  140  and  146  are disposed outside of the conveyor  10  and merely serve to transfer the respective disc grinder  122  from the first work segment  140  to the second work segment  142  and reverse.  
         [0045]     The work segments  140  and  142  are configured to be linear, meaning rectilinear, and are oriented exactly across the direction of transport of the workpieces  112 . This arrangement of the disc grinders  122  ensures that the disc grinders  122  extend uniformly over the entire width of the workpiece, independent of the actual width of the individual workpiece. Moreover, it is thus achieved that the disc grinders  122  are caused to move over the workpieces  112  at a uniform speed so that machining of the workpiece surface is perfectly uniform. In thus designing the grinding station  114 , the surface of the workpiece is optimally ground across the direction of transport and by having the disc grinders  122  rotating about their vertical axis  130  the workpiece  112  is also ground at a great variety of different angles. It has thereby been found advantageous to adjust the distance between two neighboring disc grinders  122  as a function of the infeed direction of the workpieces  112  in such a manner that a grinding tool  122  is passed over actually each point of the workpiece surface.  
         [0046]     The entire grinding station is height adjustable by means of a hoist, thus being capable of machining workpieces of different sizes.  
         [0047]      FIG. 4  illustrates a second embodiment of a continuous through-feed grinding machine of the invention that only differs from the first embodiment by the kind of drive used for the disc grinder  222 . In this embodiment, each disc grinder  222  has its own electric motor  248  that drives the vertical axis  224  of the disc grinder  222 . In an embodiment that has not been illustrated herein, each disc grinder  222  is individually driven.  
         [0048]     To supply the electric motors  248  with energy, an open power supply line  250 , which has not been illustrated in detail herein, is mounted in the inner side of the guide rail  230 . On the electric motor  248 , there is provided a corresponding sliding contact  252  that is carried along by the disc grinder  222  and rests against the power supply line  250 . Through this sliding contact  252 , the electric motor  248  can be supplied with power at any time.  
         [0049]     In a preferred developed implementation that has not been illustrated in detail herein, a control line is additionally mounted in the guide rail and a corresponding control device to the electric motor so that each electric motor of every single grinding disc can be individually controlled. This makes it even easier to individually control the various grinding tools.  
         [0050]     The  FIGS. 5 and 6  illustrate a third embodiment of a continuous through-feed grinding machine of the invention in which the grinding tools retained on the grinding station  314  are configured to be roll grinders  323 . Said roll grinders  323  are driven by an electric motor  348  and rotate about their rotation axis  354 . In the illustration according to  FIG. 5 , the roll grinders  354  are disposed in the infeed direction, meaning the rotation axis  354  is oriented at right angles to the direction of movement of the roll grinder  323  (revolving direction). As a result, the rotation axis  354  is coaxial with the direction of transport of the workpieces  312 .  
         [0051]     The electric motor  348  is retained in a frame  356  to which the roll grinder  323  is also secured, said roll grinder  323  being driven by the electric motor  348  via a V-belt  358 . The frame  356  is retained on the carriage  326  by a screw  360 , said carriage being guided on the guide rail  330 . A peripheral power supply line  350  through which the necessary power is carried to the electric motor  348  is mounted parallel to the guide rail  330 . The power supply line  350  is thereby configured to be a contactless energy transfer rail.  
         [0052]     The  FIGS. 7 through 9  also illustrate the continuous through-feed grinding machine according to the  FIGS. 5 and 6 , with the roll grinders  323  being now positioned differently. In  FIG. 7 , the roll grinders  323  are disposed so that their rotation axis is inclined at an angle of 45° to the infeed direction whilst the roll grinders  323  of  FIG. 8  are disposed across the infeed direction. In  FIG. 9 , the roll grinders are alternately disposed in the infeed direction, at an angle of 45° to the infeed direction and across the infeed direction. Three differently mounted roll grinders  323  thereby form one group of grinding tools, three such groups of grinding tools being mounted to the grinding station  314 .  
         [0053]     The discrete roll grinders  323  can readily be brought from one position to another by untightening the screw  360  and by rotating the frame  358  accordingly prior to again tightening the screw  360 . The roll grinder  323  may thus be mounted in any position.  
         [0054]      FIG. 10  illustrates a fourth embodiment that only differs from the embodiment shown in  FIG. 9  by the fact that here one group of grinding tools comprises one disc grinder  422  in addition to the three differently mounted roll grinders  423 .  
         [0055]     As a matter of course, other combinations and arrangements of the grinding tools are possible even if these are not explicitly represented herein.  
         [0056]     The grinding stations  114 ,  214 ,  314  illustrated herein can be complemented by further grinding stations  114 ,  214 ,  314  and at need by roll grinders for example that extend over the entire width of the workpiece. Also, there may be provided spindles with rotating cylinder bodies having abrasive lamellae, said spindles being disposed across the infeed direction or belt grinding units disposed across or along the infeed direction or cylinder bodies across which an abrasive paper is stretched and that are disposed across the infeed direction.  
         [0057]     In another embodiment that has not been illustrated herein, the endless path is configured as an oval or elliptical shape with the sharply curved regions being again disposed outside of the conveyor. With such an oval or elliptical endless path, the above mentioned advantages are achieved in much the same way.  
         [0058]     In still another embodiment that has not been illustrated herein, the work segments are inclined at an angle of between 45° and 135° to the direction of transport of the workpieces. Depending on the design of the workpiece surface and on their profile, such an angled arrangement may yield a further optimized grinding result.  
         [0059]     In still another embodiment that has not been illustrated herein, the grinding tools are driven with compressed air.  
         [0060]     During the actual grinding process, it is possible to cause the discrete grinding tools to rotate at different speeds or to operate discrete grinding tools in opposing directions. This depends on the respective one of the workpieces that is to be ground.  
         [0061]     It has been found out that wood or wood substitute is preferably to be ground with grinding tools at a speed of 100 to 500 rpm whilst metal is preferably to be ground at a speed of 1000 to 3000 rpm, the speed of the grinding tools revolving along the endless path being preferred to range from 1 m/min to 10 m/min. It has thereby also been found advantageous to equip the grinding station with multiple disc grinders for machining wood and wood substitutes, whereas multiple roll grinders are advantageous for machining metal. A workpiece made of wood or wood substitute is moved on the conveyor at a transport speed ranging between 1 m/min and 20 m/min whereas a workpiece made of metal is moved at a transport speed of from 0.5 m/min to 10 m/min.  
         [0062]     It has also been found advantageous to choose the speed at which the workpieces revolve to be about four times the transport speed of the workpieces in order to make certain that the grinding tool sufficiently passes over the respective workpiece.  
         [0063]     In order for the roll grinders to be readily rotatable on the grinding station, it has been found advantageous to configure the roll grinders as a square shape so that the diameter (including the abrasive means) corresponds approximately to the width of the roll.  
         [0064]     The abrasive means mounted to the grinding tools are lamellae of abrasive paper. Preferably, the back side of the lamellae rests against bristles or bristle bundles supporting the lamella.  
         [0065]     Further, pure abrasive bristles may be mounted to the disc or roll grinder for machining metal workpieces, the abrasive bristles being formed from a plastic bristle provided with an abrasive means.  
       Listing of Numerals  
       [0000]    
       
         
           
               110  conveyor  
               112 ,  312  workpiece  
               114 ,  214 ,  314  grinding station  
               116  electric drive  
               118  return pulley  
               120  chain  
               122 ,  222 ,  422  disc grinder 
             323 ,  423  roll grinder      
               124 ,  224  vertical axis  
               126 ,  326  carriage  
               128  endless path  
               130 ,  230 ,  330  guide rail  
               132  tie rod  
               134  gear wheel  
               136  gear rim  
               140  work segment  
               142  work segment  
               144  transfer segment  
               146  transfer segment 
             248 ,  348  electric motor      250 ,  350  power supply line      252  sliding contact 
                 354  rotation axis      356  frame      358  V-belt      360  screw