TWI571355B - Two-way grinding system for polishing machines - Google Patents

Description

Two-way grinding system for polishing machine

This invention relates to a polishing machine, and more particularly to a two-way grinding system for a polishing machine.

As shown in Figures 1 and 2, a polishing machine (U.S. Patent No. 5,733,180) comprises a conveyor belt 1 for transporting wood to be polished (not shown) along a length direction, and a set of four and two sets of spaces. And the sliding brush 2, the two axially spaced apart sliding saddles 3, and the two sets are respectively pivotally mounted on the sliding saddles 3 and the axial center is parallel to the length direction. a longitudinal brush wheel 4, a rocking mechanism 5 disposed between the sliding saddles 3, and a motor 6 for driving the rocking mechanism 5, the swinging mechanism 5 having a central shaft 501 and two fixed a crank 502 at both ends of the central shaft 501 and offset from each other by 180°, and two connecting rods 503 respectively pivoted between the cranks 502 and the sliding saddles 3, whereby the motor 6 is oscillated via the swing The mechanism 5 can drive the sliding saddles 3 to reciprocate the longitudinal brush wheels 4 in the lateral direction, so that the longitudinal brush wheels 4 produce a polishing direction different from the polishing of the transverse brush wheels 2 for the wood to be polished. Function; however, such a polishing machine needs to be disposed on the sliding saddles 3 respectively. Different drive motors (not shown) are used to drive the longitudinal brush wheels 4 on the individual sliding saddles 3, the number of drive motors used is large, and in order to allow the rocking mechanism 5 to be placed on the sliding saddles 3 Between the sliding saddles 3, a large spacing 301 (greater than the thickness of the individual longitudinal brush wheels 4) is required in the longitudinal direction, resulting in the sliding saddles 3 and the longitudinal direction mounted thereon. The brush wheel 4 cannot be closely arranged in the longitudinal direction, and therefore, the length of the machine of such a polishing machine in the longitudinal direction is long and takes up space.

In addition, conventional polishing machines (for example, Taiwan Patent No. M425738 or US Pat. No. 7,351,130 B1) arrange a part of the brush wheels in such a manner that the axis is inclined to the conveying direction of the conveyor belt, although different polishing directions can be produced. Polishing effect, however, the inclined arrangement of the brush wheel will inevitably occupy more space in the conveying direction, and the length of the machine of the polishing machine will be longer, and the length of the machine cannot be reduced.

Accordingly, it is an object of the present invention to provide a two-way grinding system for a polishing machine that can halve the number of motors used to drive the brush wheel and allow the front and rear brush wheels to be closely aligned.

Thus, the present invention is directed to a two-way polishing system for a polishing machine that feeds in a first direction, the two-way polishing system including a saddle, and at least one polishing device.

The grinding device is disposed on the saddle, the grinding device includes a rotatable front brush wheel unit, a rear brush wheel unit that is rotatable downstream of the front brush wheel unit in the first direction, and a driving unit The rotation axis of the front brush wheel unit is parallel to the first direction, and the rotation axis of the rear brush wheel unit is parallel to the first direction. The driving unit has a common motor, and is disposed on the common motor and the front. a front transmission mechanism between the brush wheel units, and a rear transmission mechanism disposed between the common motor and the rear brush wheel unit, wherein the common motor drives the front brush wheel through the front transmission mechanism and the rear transmission mechanism respectively When the unit and the rear brush wheel unit, the front brush wheel unit and the rear brush wheel unit rotate in opposite directions.

The utility model has the advantages that the front and rear brush wheel units are synchronously driven by the common motor, and the number of motors for driving the brush wheel is halved, and the front and rear brush wheel units can be closely arranged in the same saddle. Seat, making the overall space design more compact.

Referring to FIG. 3, an embodiment of a two-way polishing system 100 for a polishing machine 200 of the present invention has a machine table 210 and a conveyor belt 220 fed in a first direction X. The two-way grinding system 100 includes: a rail 10, a saddle 20, two grinding devices 30, and a reciprocating drive 40.

As shown in FIGS. 3 and 4, the rail 10 is disposed on the machine table 210 in a second direction Y perpendicular to the first direction X.

The saddle 20 is movably disposed on the rail 10, and the saddle 20 is slidable relative to the rail 10 in the second direction Y. In this embodiment, the saddle 20 has a top wall 21, two side walls 22 connected to the top wall 21, and eight spaced-apart fixed arms 23 having four spaced-apart slots 211. Two sets of the fixed arms 23 are disposed at the bottom ends of the side walls 22 correspondingly to each other.

As shown in FIGS. 5, 6, and 7, the grinding devices 30 are spaced apart from the saddle 20 in the second direction Y, and each of the grinding devices 30 includes two fixed to the saddle 20 and parallel to the first a spindle X in a direction X, a rotatable front brush wheel unit 60, a rear brush wheel unit 70 located downstream of the front brush wheel unit 60 in the first direction X, and a drive unit 80 .

The mandrels 50 are spaced apart from each other in the second direction Y. In the present embodiment, each mandrel 50 is fixed between the corresponding two fixed arms 23.

The rotation direction of the front brush wheel unit 60 is parallel to the first direction X, and the rotation axis of the rear brush wheel unit 70 is parallel to the first direction X. In the embodiment, the front brush wheel unit 60 has two a front brush wheel 61 spaced apart in the second direction Y, the rear brush wheel unit 70 has two rear brush wheels 71 spaced apart in the second direction Y, and the front brush wheels 61 are respectively pivoted at the same One end portion of the mandrel 50 is pivotally disposed at the other end of the mandrel 50, and the front brush wheel 61 of the front brush wheel unit 60 and the front brush wheel of the rear brush wheel unit 70 61 is coaxially disposed in the first direction X, and the rear brush wheels 71 correspond to the front brush wheels 61, respectively.

In the present embodiment, each of the front brush wheels 61 has a front hub 611, a plurality of front bristle rows 612 disposed on the front hub 611, a rotation axis 613 parallel to the first direction X, and one at the first The wheel thickness W in the direction X. The front hub 611 has two end faces 614, and an outer peripheral surface 615 connected between the end faces 614. The outer peripheral surface 615 of the front hub 611 forms a plurality of front positioning grooves 616 extending to the end faces 614, each front positioning The direction in which the groove 616 extends from one of the end faces 614 to the other end face 614 is inclined to the axis of rotation 613. The inner ends of each of the front bristle rows 612 are disposed in respective front positioning grooves 616, each of the front bristle rows 612 having a plurality of bristles 617 extending outwardly from the respective front positioning grooves 616 and extending in a direction oblique to the axis of rotation 613. Similarly, each rear brush wheel 71 has a rear hub 711, a plurality of rear bristle rows 712 disposed on the rear hub 711, an axis of rotation 713 parallel to the first direction X, and a first direction X. The wheel thickness is W. The rear hub 711 has two end faces 714, and an outer peripheral surface 715 connected between the end faces 714. The outer peripheral surface 715 of the rear hub 711 forms a rear positioning groove 716 extending to the end faces 714, and each rear positioning The direction in which the groove 716 extends from one of the end faces 714 to the other end face 714 is inclined to the axis of rotation 713. The inner ends of each of the rear bristle rows 712 are disposed in respective rearward positioning grooves 716, and each of the rear bristle rows 712 has a plurality of bristles 717 extending outwardly from the individual rearward positioning grooves 716 and extending in a direction oblique to the axis of rotation 713.

A gap H is formed in the first direction X between the front brush wheel 61 and the rear brush wheel 71 on the same spindle 50, and the gap H is smaller than the wheel thickness of the front brush wheel 61 and the rear brush wheel 71. One-half of W.

The driving unit 80 has a common motor 81, a front transmission mechanism 82 disposed between the common motor 81 and the front brush wheel unit 60, and a common motor 81 and the rear brush unit 70. Rear transmission mechanism 83.

The common motor 80 has an output shaft 811. In this embodiment, the output shaft 811 is parallel to the second direction Y.

The front transmission mechanism 82 has a first pulley 821 disposed on the output shaft 811, a second pulley 822, a first belt 823 and a third pulley disposed on the first pulley 821 and the second pulley 822. 824. The fourth pulley 825 is respectively disposed on the mandrel 50 and is respectively fixed to the front hub 611 of the front brush wheel 61, and the set is disposed on the third pulley 824 and the fourth pulley 825. A second belt 826 that passes through one of the slots 211 (see FIG. 4) of the saddle 20, and a front reducer 827 that is coupled between the second pulley 822 and the third pulley 824. In the present embodiment, the front reducer 827 has a worm 828 disposed coaxially with the second pulley 822, and a worm gear 829 coaxially disposed with the third pulley 824 and engaged with the worm 828.

The rear transmission mechanism 83 has a fifth pulley 831 disposed on the output shaft 811, a sixth pulley 832, a third belt 833 disposed on the fifth pulley 831 and the sixth pulley 832, and a seventh pulley. 834. The eighth pulley 835 is respectively disposed on the mandrel 50 and fixed to the rear hub 711 of the rear brush wheel 71, and the set is disposed on the seventh pulley 834 and the eighth pulley 835. A fourth belt 836 that passes through the other slot 211 (see FIG. 4) of the saddle 20, and a rear reducer 837 that is coupled between the sixth pulley 832 and the seventh pulley 834. In the present embodiment, the rear reducer 837 has a worm 838 disposed coaxially with the sixth pulley 832, and a worm gear 839 disposed coaxially with the seventh pulley 834 and engaged with the worm 838.

In this embodiment, the rotation axes of the first, second, fifth, and sixth pulleys 821, 822, 831, and 832 are parallel to the second direction Y, and the third, fourth, seventh, and eighth The rotational axes of the pulleys 824, 825, 834, 835 are parallel to the first direction X, and the first and fifth pulleys 821, 831 are integrally connected.

When the common motor 81 drives the front brush wheel unit 60 and the rear brush wheel unit 70 via the front transmission mechanism 82 and the rear transmission mechanism 83, the front brush wheel 61 and the rear brush wheel of the front brush wheel unit 60 are respectively driven. The rear brush wheel 71 of the unit 70 is reversely rotated. In the present embodiment, the front brush wheel 61 is viewed from the front brush wheel 71, and the front brush wheel 61 is rotated clockwise. 71 is a counterclockwise rotation.

It can be understood that the front transmission mechanism 82 and the rear transmission mechanism 83 can be designed with the same or different reduction ratios, so that the front brush wheels 61 and the rear brush wheels 71 generate the same or different rotation speeds.

As shown in FIGS. 3 and 8, the reciprocating drive unit 40 includes a guide rack 41 fixed to the rail 10 in the second direction Y, a drive disposed on the saddle 20 and having an output shaft 421. a motor 42 , a driving wheel 43 disposed on the output shaft 421 and meshing with the guiding pinion 41 , and two idler wheels 44 pivotally disposed on the saddle 20 and symmetrical to the driving wheel 43 are disposed at intervals The switch frame 10 and the switch plate 45 outside the two ends of the saddle 20 in the second direction Y, and two are respectively disposed at two ends of the saddle 20 and interposed between the switch plates 45 Limit switch 46. In the present embodiment, the guide rack 41 is a belt which allows the guide rack 41 to be tightened on the drive wheel 43.

The driving motor 42 can drive the driving wheel 43 to reciprocate relative to the guiding rack 41 along the second direction Y belt to drive the saddle 20 and the grinding device 30 along the rail 10 along the second The direction Y reciprocates, it can be understood that, in the embodiment, in the manner of control, the limit switch 46 can be used to control the steering of the output shaft 421 of the drive motor 42. For example, as shown in FIG. As shown, the driving motor 4 can drive the driving wheel 43 clockwise to drive the saddle 20 and the grinding device 30 to move to the left side of FIG. 3 relative to the rail frame 10, and the limit switch to be located on the left side. When the corresponding switch panel 45 is touched, the drive motor 4 can reversely drive the drive wheel 43 to rotate counterclockwise to drive the saddle 20 and the grinding device 30 relative to the rail frame 10 When the limit switch 46 on the right side touches the corresponding switch plate 45, the drive motor 4 can reversely drive the drive wheel 43 to rotate clockwise. Thus, the reciprocating drive 40 That is, the saddle 20 and the grinding devices 30 can be opposed to the rail 10 Reciprocating along the second direction Y.

Thereby, as shown in FIGS. 3, 6, and 7, when the conveyor belt 220 of the polishing machine 200 conveys a wood to be polished (not shown) along the first direction X, each of the polishing devices 30 is rotated in the reverse direction. The brush wheel 61 and the rear brush wheel 71 can produce a polishing effect of different polishing directions on the wood to be polished to uniformly polish and reduce the generation of polishing dead angles, and at the same time, the reciprocating driving device 40 can synchronously let the saddle The seat 20 and the grinding device 30 reciprocate relative to the rail frame 10 in the second direction Y such that the front brush wheel 61 and the rear brush wheel 71 can be in the second direction Y of the wood to be polished. The entire range of polishing is performed to avoid the incomplete polishing of the wood to be polished.

In addition, it can be understood that the two-way grinding system 100 of the present invention can of course be used in combination with the transverse brush wheel of the conventional polishing machine (US Pat. No. 5,733,180) parallel to the transverse direction (ie, the second direction Y). Or in combination with a conventional polishing machine (Taiwan New Patent No. M425738) with a shaft parallel to the height direction (ie, perpendicular to the first and second directions X, Y), or in one Two bidirectional grinding systems 100 of the present invention are placed on the polishing machine to produce a more comprehensive polishing action.

Through the above description, the advantages of the present invention can be further summarized as follows:

1. The front and rear brush wheels 61, 71 of each grinding device 30 of the present invention can share the common motor 81 of the driving unit 80. Compared with the prior art, in the case where the number of brush wheels being driven is the same, The present invention can halve the number of motors used and reduce manufacturing costs.

2. The front and rear brush wheels 61, 71 of each grinding device 30 of the present invention are disposed on the same saddle 20, and the front and rear brush wheels 61, 71 are closely arranged in the first direction X. Compared with the prior art, the space design of the invention in the first direction X is more compact, and the length required for the machine table 210 of the polishing machine 200 in the first direction X is effectively reduced, thereby saving the overall occupation. Space.

3. The direction in which the bristles 617 of the front bristle row 612 of the front brush wheel 61 of the present invention extend outward is inclined to the axis of rotation 613 of the front brush wheel 61, and the bristles of the rear bristle row 712 of the rear brush wheel 71 The direction in which the 717 extends outward is also inclined to the axis of rotation 713 of the rear brush wheel 71, such that, in addition to reducing the bristles of the preceding and following brush wheels 61, 71, the wood to be polished which is advanced in the first direction X is encountered. The resistance received at 617 and 717 can also prevent the bristles 617, 717 of the front and rear brush wheels 61, 71 from being directly bent by the wood to be polished which is moved forward, but, more importantly, compared The front and rear brush wheels 61, 71 are arranged in such a manner that the rotation axis is parallel to the first direction X, which can effectively reduce the front and rear brush wheels 61, The space occupied by the first direction X is further reduced by the length required for the machine table 210 of the polishing machine 200 in the first direction X.

In summary, the two-way grinding system for the polishing machine of the present invention can not only halve the number of motors required for driving the brush wheel, but also closely arrange the front and rear brush wheels to make the overall space design more compact. Therefore, the object of the present invention can be achieved.

However, the above is only the embodiment of the present invention, and the scope of the invention is not limited thereto, and all the equivalent equivalent changes and modifications according to the scope of the patent application and the patent specification of the present invention are still The scope of the invention is covered.

200‧‧‧ polishing machine
210‧‧‧ machine
220‧‧‧ conveyor belt
100‧‧‧Two-way grinding system
10‧‧‧rails
20‧‧‧ saddle
21‧‧‧ top wall
211‧‧‧through slot
22‧‧‧ side wall
23‧‧‧Fixed Arm
30‧‧‧ grinding device
40‧‧‧Reciprocating drive
41‧‧‧Guided rack
42‧‧‧Drive motor
421‧‧‧ Output shaft
43‧‧‧Drive wheel
44‧‧‧ Idler
45‧‧‧Switch panel
46‧‧‧Limit switch
50‧‧‧ mandrel
60‧‧‧ front brush wheel unit
61‧‧‧Pre-brush wheel
611·‧‧‧ front wheel hub
612‧‧‧Pre-hair row
613‧‧‧Rotation axis
614‧‧‧ end face
615‧‧‧ outer perimeter
616‧‧‧ front positioning groove
617‧‧‧ bristles
70‧‧‧Back brush unit
71‧‧‧Back brush wheel
711‧‧‧ rear wheel hub
712‧‧‧ rear brush row
713‧‧‧Rotation axis
714‧‧‧ end face
715‧‧‧ outer perimeter
716‧‧‧ rear positioning ditch
717‧‧‧ bristles
80‧‧‧ drive unit
81‧‧‧Shared motor
811‧‧‧ Output shaft
82‧‧‧Front transmission
821‧‧‧First pulley
822‧‧‧Second pulley
823‧‧‧First belt
824‧‧‧ Third pulley
825‧‧‧fourth pulley
826‧‧‧Second belt
827‧‧‧Front reducer
828‧‧‧ worm
829‧‧‧ worm gear
83‧‧‧ Rear transmission mechanism
831‧‧‧ fifth pulley
832‧‧‧6th pulley
833‧‧‧ Third belt
834‧‧‧ seventh pulley
835‧‧‧8th pulley
836‧‧‧fourth belt
837‧‧‧ Rear reducer
838‧‧‧ worm
839‧‧‧ worm gear
X‧‧‧ first direction
Y‧‧‧second direction
W‧‧‧ wheel thickness
H‧‧‧ gap

Other features and effects of the present invention will be apparent from the following description of the drawings, wherein: Figure 1 is a front view of a conventional polishing machine; Figure 2 is a four-way brush wheel, two sliding of the polishing machine 3 is a perspective view of a side view of a two-way grinding system for a polishing machine of the present invention; FIG. 4 is a perspective view of a rail and a saddle of the embodiment. FIG. 5 is an exploded perspective view of a fourth pulley, a front brush wheel, a mandrel, a rear brush wheel and an eighth pulley of the embodiment; FIG. 6 is a rail frame and a saddle of the embodiment. FIG. 7 is a partial cross-sectional view taken along line VII-VII of FIG. 6; and FIG. 8 is an incomplete top view illustrating a reciprocating transmission of the embodiment.

10‧‧‧rails

20‧‧‧ saddle

23‧‧‧Fixed Arm

30‧‧‧ grinding device

50‧‧‧ mandrel

60‧‧‧ front brush wheel unit

61‧‧‧Pre-brush wheel

611‧‧‧ front wheel hub

612‧‧‧Pre-hair row

613‧‧‧Rotation axis

70‧‧‧Back brush unit

71‧‧‧Back brush wheel

711‧‧‧ rear wheel hub

712‧‧‧ rear brush row

713‧‧‧Rotation axis

80‧‧‧ drive unit

81‧‧‧Shared motor

811‧‧‧ Output shaft

82‧‧‧Front transmission

821‧‧‧First pulley

822‧‧‧Second pulley

823 first belt

824‧‧‧ Third pulley

825‧‧‧fourth pulley

826‧‧‧Second belt

827‧‧‧Front reducer

828‧‧‧ worm

829‧‧‧ worm gear

83‧‧‧ Rear transmission mechanism

831‧‧‧ fifth pulley

832‧‧‧6th pulley

833‧‧‧ Third belt

834‧‧‧ seventh pulley

835‧‧‧8th pulley

836‧‧‧fourth belt

837‧‧‧ Rear reducer

838‧‧‧ worm

839‧‧‧ worm gear

X‧‧‧ first direction

Y‧‧‧second direction

W‧‧‧ wheel thickness

H‧‧‧ gap

Claims (10)

A two-way grinding system for a polishing machine, the polishing machine feeding in a first direction, the two-way polishing system comprising: a saddle; and at least one grinding device disposed on the saddle, the grinding device comprising a rotatable a front brush wheel unit, a rear brush wheel unit that is located downstream of the front brush wheel unit in the first direction, and a driving unit, the rotation axis of the front brush wheel unit being parallel to the first direction, The rotation direction of the rear brush wheel unit is parallel to the first direction, and the driving unit has a common motor, a front transmission mechanism disposed between the common motor and the front brush wheel unit, and a common motor disposed on the common motor a rear transmission mechanism with the rear brush wheel unit, when the common motor drives the front brush wheel unit and the rear brush wheel unit via the front transmission mechanism and the rear transmission mechanism, respectively, the front brush wheel unit and the rear The brush wheel unit rotates in the reverse direction. A two-way grinding system for a polishing machine according to claim 1, wherein the front brush wheel unit and the rear brush wheel unit are coaxially disposed in the first direction. A two-way grinding system for a polishing machine according to claim 2, wherein the front brush wheel unit has at least one front brush wheel, the rear brush wheel unit having at least one rear brush wheel, the front brush wheel having a front wheel hub And a front bristles disposed on the front hub, the front hub having two end faces, and an outer peripheral surface connected between the end faces, the outer peripheral surface of the front hub forming a plurality of front positioning grooves extending to the end faces The extending direction of each front positioning groove extending from one end surface to the other end surface is inclined to the rotation axis, and each front bristle row is disposed in an individual front positioning groove, and each front bristle row has a plurality of individual front positioning grooves. a bristles extending outwardly and extending obliquely to the axis of rotation, the rear brush wheel having a rear hub and a plurality of rear bristles disposed on the rear hub, the rear hub having two end faces, and a connecting end face The outer peripheral surface of the rear hub forms a plurality of rear positioning grooves extending to the end faces, and the extending direction of each rear positioning groove extending from one end surface to the other end surface is inclined to the rotation axis, and each rear bristles Arrangement Placed in individual rearward positioning grooves, each of the rear rows of bristles having a plurality of bristles extending outwardly from the respective rearwardly located grooves and extending obliquely to the axis of rotation. The two-way grinding system for a polishing machine according to claim 2, wherein the front brush wheel unit has two front brush wheels spaced apart in a second direction perpendicular to the first direction, each front brush wheel Having a rotation axis parallel to the first direction, the rear brush wheel unit has two rear brush wheels spaced apart in the second direction, each rear brush wheel having a rotation axis parallel to the first direction, The rear brush wheels correspond to the front brush wheels, respectively. The two-way grinding system for a polishing machine according to claim 4, wherein the grinding device further comprises two mandrels fixed to the saddle and parallel to the first direction, the mandrels being in the second direction The front brush wheels are respectively disposed at one end of the mandrels, and the rear brush wheels are respectively pivotally disposed at the other ends of the mandrels. The two-way grinding system for a polishing machine according to claim 5, wherein the common motor has an output shaft, and the front transmission mechanism has a first pulley, a second pulley, and a set provided on the output shaft. a first pulley, a third pulley, and a second pulley respectively disposed on the first pulley and the second pulley and fixed to the front brush wheel respectively, and the set is disposed on the first pulley and the second pulley a third pulley and a second belt of the fourth pulley, and a front reducer connected between the second pulley and the third pulley, the rear transmission mechanism having a fifth pulley disposed on the output shaft, a sixth pulley, a third belt disposed on the fifth pulley and the sixth pulley, a seventh pulley, and an eighth pulley respectively pivoted on the spindles and respectively fixed to the rear brush wheels And a fourth belt disposed on the seventh pulley and the eighth pulleys, and a rear reducer connected between the sixth pulley and the seventh pulley. The bidirectional grinding system for a polishing machine according to claim 6, wherein the output shaft of the common motor is parallel to the second direction, and the rotation axes of the first, second, fifth, and sixth pulleys are parallel In the second direction, the rotation axes of the third and seventh pulleys are parallel to the first direction, the front reducer has a worm coaxially disposed with the second pulley, and a coaxially disposed with the third pulley a worm gear meshing with the worm, the rear reducer having a worm disposed coaxially with the sixth pulley, and a worm gear coaxially disposed with the seventh pulley and engaging the worm. The two-way grinding system for a polishing machine according to claim 2, wherein the front brush wheel unit has at least one front brush wheel, and the rear brush wheel unit has at least one rear brush wheel, the front brush wheel having a a wheel thickness in a first direction, the rear brush wheel has a wheel thickness in the first direction, and a gap is formed between the front brush wheel and the rear brush wheel in the first direction, the gap being smaller than the front brush wheel One-half the thickness of the wheel with the rear brush wheel. The two-way grinding system for a polishing machine according to claim 1, further comprising a rail disposed along a second direction perpendicular to the first direction, and a reciprocating driving device, the saddle being movably disposed on The reciprocating driving device includes a guiding rack fixed to the rail in the second direction, a driving motor disposed on the saddle and having an output shaft, and a driving shaft disposed on the output shaft a driving wheel engaged with the guiding pinion for driving the driving wheel to reciprocate in the second direction relative to the guiding pin to drive the saddle and the grinding device relative to the rail Reciprocating in the second direction. The two-way grinding system for a polishing machine according to claim 9, wherein the reciprocating driving device further comprises two idlers pivoted to the saddle and symmetrical to the driving wheel, the idler wheels making the guiding teeth The rail is tightened on the drive wheel, which is a belt.