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(11) | EP 0 250 117 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Positive workpiece drive machine and method |
| (57) A positive workpiece drive machine comprises a positive endless drive belt (106)
for forwarding workpieces (20) or other parts to a workpiece grinder (16). The drive
belt (106) adjusts for variations in workpiece thickness and creates the high output
force necessary to push a train of the workpieces through a pair of grinding wheels
(112, 114). This drive machine also includes a precise hold-down air spring (150) which, in the specific application to the grinding of fragile ceramic magnet blanks, is gentle to the magnet blanks while providing the required positive drive. |
[0002] Prior to the present invention, endless-belt workpiece drive systems were used to serially feed parts or other workpieces through grinders and other types of machinery which inherently resist workpiece input. Although such systems were an improvement over other feeders, they did not accept a wide size range of workpieces, and they did not provide sufficient feed force to effectively and efficiently feed the workpieces through resistive work forces such as are encountered in part-grinding machines. The prior system also caused many workpieces to break, particularly those of brittle ceramic material used for magnet blanks, so resulting in increased part cost and excessive "down time" for machine repair and cleaning.
[0003] The present invention is concerned with the provision of a positive workpiece drive machine in the form of a part drive assembly by means of which fragile workpieces, for example magnet blanks of brittle ceramic, can be fed into the high resistance of a grinder or other type of machinery without breakage.
[0004] To this end a part drive assembly in accordance with the present invention comprises the combination of features specified in claim 1.
[0005] In contrast to the prior drive systems, a part drive assembly in accordance with the present invention utilises a new and improved endless belt workpiece drive system having a linear drive force which makes it possible to effectively feed a line of abutting workpieces into a work station, for example a grinding machine, and counter to the grinding force produced by opposing grinding wheels driven by high-horsepower motors. Such a part drive assembly has the potential to feed without breaking or otherwise damaging workpieces of brittle material, such as ceramic material used to make high-quality permanent magnets. Such materials are often highly abrasive, and have caused abrasion and wear of prior machinery for handling such workpieces, thus often involving extensive down-time for maintenance and replacement of parts.
[0006] With the new and improved construction provided by the present invention, less maintenance is required, and the part-drive components potentially have a longer service life.
[0007] With the construction provided by the present invention, also, tooling can be adjusted to accommodate new workpiece shapes, without the need for replacement by different-sized drive belts and other components.
[0008] These results are made possible by a part drive assembly in accordance with the present invention, inasmuch as such an assembly provides a positive-type part drive which utilises a drive belt with a resilient frictional drive surface that automatically conforms to the shape of workpieces, for a more positive and gentle gripping of the parts being driven.
[0009] The part drive assembly in accordance with the present invention thus makes available an effective means for feeding workpieces to a work station, and more particularly a highly efficient workpiece driver which has the potential to accommodate a wide size range of workpieces and provide a positive force to firmly and gently grip and automatically feed a train of separate workpieces, even through machinery providing a high resistive force to the feed drive.
[0010] A part drive assembly in.accordance with the present invention thus represents a new and improved workpiece driver which utilises an endless drive belt having an outer drive surface that readily conforms to the contoured surfaces of the workpieces and which accommodates a wide variation in size of the workpieces being driven.
[0011] A part drive assembly in accordance with the present invention may utilise a new and improved air hold-down of the drive belt as it is driving the workpieces, to ensure that all the parts are positively driven in a train into a work station, and to accommodate a wide range of part sizes and tolerances. An advantageous feature of the invention is the available low-friction support of the workpieces as they are being fed in an abutting train into the resistive force of grinding wheels or other types of part-working machine.
[0012] The present invention inter alia makes available a new and improved positive-type workpiece driver which can automatically adjust for variation in workpiece shape and thickness while exerting a constant and slip-clutch-limited high output force necessary to push fragile blanks through oppositely opposed grinding wheels which simultaneously grind the outer and inner surfaces of these blanks.
[0013] It is thus possible to have a continuous in-line workpiece drive machine that has the drive force necessary to push a series of contacting workpiece blanks through grinding wheels which finish the parts.
[0014] In a preferred embodiment of a part drive assembly in accordance with the present invention, the part drive assembly includes a specially designed gear-drive belt that provides positive transfer drive, and has a high-strength corded elastomeric inner belt part that provides a surface for back-up rollers, as well as drive teeth for co-operation with a drive sprocket. The belt has an outer surface of a soft rubber material forming a backing which is bonded or otherwise secured to the inner belt part to provide the surface contact necessary to positively grip the magnet blank parts and prevent slippage. Co-operation between the upper rollers (that is, the back-up rollers) and the belt allows the soft rubber of the belt to conform to the curved surface of the magnet blanks. Lower rollers provide continuous low-friction support and improved transfer of the magnet blanks to the grinding wheels. Air springs pushing down on an upper roller mounting block provide the force necessary to conform the soft rubber to the surface of the magnets and allow for variation in part thickness. If the magnets become jammed after leaving the part drive station, an adjustable air-operated overload clutch prevents the drive belt from slipping on the train of magnet blanks, thereby eliminating belt damage to the blanks. The entire part drive station is mounted for vertical movement, to provide clearance under the drive belt for the clearing of jams and for servicing of the tooling.
[0015] The invention further relates to a method of force-feeding a plurality of substantially identical and contoured workpieces into a resistive force of a pair of opposed grinding wheels, specifically by the use of the measures specified in claim 9. This method makes possible the positive gripping and feeding of workpieces through machinery which exerts a high resistive work force counter to the feeding drive force.
[0017] In the drawings:
Figure 1 is a diagrammatic side view of a preferred embodiment of a part drive assembly in accordance with the present invention embodied in a part or other workpiece grinding machine having a part drive station and a part conveyer;
Figure 2 is a side view of the part drive station of the grinding machine of Figure 1;
Figure 3 is a view partly in section on the line 3--3 of Figure 2, in the direction of the arrows;
Figure 4 is an end view of the part drive station of Figure 2,,on the line 4--4 of Figure 2, in the direction of the arrows;
Figure 5 is a fragmentary sectional view, with parts shown in elevation, on the line 5--5 of Figure 2, in the direction of the arrows, showing a portion of the part drive station;
Figure 6 is a fragmentary side view, partly in section, illustrating the construction of a drive belt in conformity with the present invention;
Figure 7 is a top view on the line 7--7 of Figure 2, in the direction of the arrows, showing lower support tooling and a train of parts to be ground; and
Figure 8 is a fragmentary sectional view, with parts in elevation, on the line 8--8 of Figure 2, in the direction of the arrows, showing a part overload clutch.
[0018] With reference now to the drawings, Figure 1 shows a part grind and feed machine 10 which generally comprises a conveyor 12, a part drive station 14 and a grinder 16. A series of individual parts 20, in this embodiment partially cylindrical workpieces of strontium ferrite material forming magnet blanks to be ground and subsequently magnetised, are loaded on to a track formed by an endless polyurethane belt 22 that extends around sprockets 24 and 26 which are rotatably mounted on opposite ends of a horizontal support 28 that is in turn supported by uprights 29 and 30 each having a foot pad 31 supported on a floor 32. The conveyer 12 is tied to the base 33 of the machine 10 by means of a suitable bracket 34 and threaded fasteners 36. A variable-speed DC motor 38 supported by the upright 29 drives the sprocket 24 by way of a drive belt or chain 40, so that the polyurethane belt 22 is driven to advance the parts 20 into the part drive station 14 in conformity with the present invention. The load conveyor preferably runs about 10% faster than the part drive, for part stack-up.
[0019] The part drive station 14 is best seen in Figures 2 and 4, and includes a DC motor 46 that drives a tachometer 47 and a speed reducer 49, which in turn drives an upper sprocket 48 that is mounted on a vertically adjustable support plate 50. The upper sprocket 48 drives a drive overload clutch assembly 54 that is shown in detail in Figure 8. This assembly 54 incorporates a spindle 56 extending laterally from a main support plate 58. A drive sprocket 60 is rotatably mounted on the spindle 56 and is driven by the upper sprocket 48 by way of an endless chain 62. The drive sprocket 60 is secured to a hub plate 63 that is rotatably mounted on the spindle by means of a bearing 64. An annular disc 66 of friction material is secured to the side face of the hub plate 63 by means of threaded fasteners 68.
[0020] A drive belt sprocket 72 is rotatably mounted on the spindle 56 by means of a pair of side-by-side bearings 74, and has a frictional side surface 76 that is operatively engageable with the friction disc 66 by the application of a selected side force from an air spring piston 78 which is operatively mounted in a cover 80 mounted on the spindle 56. A plurality of helical clutch apply springs 82 are mounted between the cover 80 and the axially movable piston 78, and provide a spring apply force to effect driving engagement of the drive belt sprocket 72 with the friction disc 66. In this preferred embodiment, the piston 78 has an annular contact 81 on the inboard side surfaces which bears against the inner race 83 of the outboard bearing 74, and the resulting side force is transmitted by the ball-bearing assemblies to the inner flange 84 of the drive belt sprocket 72.
[0021] With this pneumatically generated apply force supplementing that of the helical springs 82, there is a predetermined frictional drive of the belt drive sprocket 72 by way of the chain drive sprocket 80.
[0022] 0-ring seals 86 and 88 are sealingly interposed between the inner diameter of the air spring piston 78 and the cylindrical spindle 56, and between the outer diameter of the piston 78 and the cover 80, to effect air sealing of this element. The cover 80 is fixed to the outer end of the spindle by means of a threaded fastener 90. An O-ring face seal 92 prevents air leakage from an inner air pressure chamber 94 that is pneumatically connected by means of air passages 98, 100, 102 and 104 to a source 96 of regulated pressure air.
[0023] With this arrangement, air pressure will act on the piston 78 to transmit an axial drive force to the drive belt sprocket 72. This force can be readily increased or decreased by correspondingly increasing or decreasing the force of the regulated air pressure. With this slipping clutch arrangement, the drive belt sprocket will slip if the drive belt 106 which moves the parts 20 from the conveyer belt into the grinder 16 is overloaded. This protects the machinery, and prevents breakage of, or other damage to, the workpiece 20.
[0024] The drive belt 106 is a composite endless belt best seen in Figure 6 as having a toothed inner belt portion 108, which may be made of a cord-reinforced elastomeric material, on which is bonded a soft foam rubber backing (outer portion) 110. This backing may be of a suitable closed-cell foam rubber material having a durometer hardness of 40. The belt 106 is driven in a clockwise direction by the driving engagement of the teeth of the drive sprocket with the teeth of the belt. As is best illustrated in Figure 3, the soft foam rubber backing 110 of the lower segment of the belt 106 that runs between the lower pulleys is pressed downwardly to automatically conform to the cylindrical shape of the train of abutting parts 20, regardless of size variation, to provide uniform loading and positive- friction drive of the parts for effective feed between the grinding wheels 112 and 114 of the grinder 16. Furthermore, this foam backing readily conforms to any profile variations and shapes of the workpieces, and more surface area is contacted and gripped by the drive belt.
[0025] As is best seen in Figure 2, the belt 106 as driven by the drive belt sprocket 72 wraps around a gear belt idler pulley 120 rotatably mounted on the outwardly extending spindle of an adjustment plate 122 the fore and aft position of which can be adjusted by means of a hand wheel 124 for selective tensioning of the drive belt 106. By turning of the hand wheel 124 to a predetermined position to remove the idler pulley 120 from effective contact with the belt, belt changing is facilitated. After the part drive belt 106 has been installed and an appropriate tension has been selected, threaded fasteners 126 extending through longitudinally extending adjustment slots 128 are tightened down to maintain the selected belt tension.
[0026] From the tension adjustment pulley 120, the part drive belt 106 is routed around a pair of longitudinally spaced lower guide pulleys 129 and 130 horizontally mounted,on spindles 132 and 134 that extend from the support plate 58. The belt then feeds upwardly and back to the drive belt sprocket 72.
[0027] An important feature of the present invention is an upper and lower pair of tooling assemblies 142 and 144. The upper tooling assembly 142 comprises a support block 146 suitably secured to the support plate 58. Secured to the top of the support block 146 are a pair of air spring assemblies 150 each having an air piston housing 152 secured by threaded fasteners 154 on the top of the support block 146. Pistons 156 are mounted in these housings and have a downwardly extending pressure rod 157 that extends downwardly through the support block 146 into contact with the upper surface of a pressure block 158 which is mounted for vertical movement within the confines of the support block 146. Vertical slide bushings 159 are used for guiding and limiting the vertical movement of the pressure block 158.
[0028] As is shown in Figures 2 and 3, the pressure block 158 carries at its lower end a longitudinally extending series of back-up rollers 160 which fit in a central groove 162 of the inner part of the part drive belt 106 and extend along the top of the drive belt from the pulley 129 to the pulley 130. A regulated source of pressure air 164, shown diagrammatically in Figure 2, supplies pressure air to the top of the pistons 156, so that a constant pressure is applied by way of the pressure block 158, the upper back-up rollers 160 and the part drive belt 106 to each of the workpieces 20. The foamed surface of the drive belt 106 will grip the arcuate top of the workpieces with a constant gripping force, to effect the required lateral feed of the parts into the grinding wheels 112 and 114 when the part drive belt 106 is driven in a clockwise direction. This gripping force, although high, is cushioned by the resiliency of the closed-cell part drive backing of the belt 106 so that the workpieces will not be destroyed or otherwise damaged by the downward force of the drive belt.
[0029] The lower support tooling assembly 144 has a support block 166 secured to the base of the machine. An elongate carrier 168 for lower rollers 170 closely arranged in series and supported by pins 172 is mounted for vertical adjustable movement on the support block 166. As is shown in Figure 5, these rollers 170 contact the centre-line of the inner surfaces of the workpieces 20, and fully support these parts with reduced friction, so that the workpieces are readily fed by the drive belt 106, with good support, into the grinder 16. Vertical slots 174 in the carrier 168 receive threaded fasteners 176 that thread into the support block 166. This fastener and slot arrangement provides for the vertical adjustment movement of the lower carrier 168 for supporting the workpieces 20. Screws 180 threaded through the support block 166 engage the bottom of the carrier 168 to hold the carrier in its adjusted position.
[0030] A pair of laterally spaced upper and lower carbide rails 184 and 185 shown in Figures 4, 5 and 7 are secured to the upper surface of the support block 166 by means of threaded fasteners 182, and form an elongate channel-like track 183 for guiding the workpieces 20 as they are moved in a train from the conveyer belt. Similar tracks 186 are provided adjacent the pulley 130 for guiding the workpieces 20 into the grinder. A power cylinder 187 and suitable controls are employed to move the support plate and tooling off the workpieces to permit the clearance of jammed parts, or tooling repairs, if needed.
[0031] The part drive station 14 develops sufficient drive force to push-feed the train of abutting workpieces 20 between the outside-radius and inside-radius grinding wheels 112 and 114, while accommodating variations in thickness of the workpieces 20 by virtue of the resilience of the foam rubber backing of the drive belt 106. The workpieces 20, after having their outer and inner surfaces ground, are pushed by the force of the drive belt 106 between a foot grinding wheel 188 and a hold-down rack 198. After leaving the foot grinding wheel 188, the workpieces 20 are fed through a wash enclosure 190, where the workpieces are washed by pressure water fed through nozzles 192. While still on their tracks, the workpieces 20 pass through a drying enclosure 194 which uses compressed air fed through nozzles 196 to dry the workpieces. The hold-down rail 198 may be movable upwardly to a retracted position to clear the relevant workpieces if required.
[0032] From the drying enclosure, the workpieces 20 are fed to a chute-like discharge tray 200, from which they may be removed to be magnetised or for other subsequent treatment.
[0033] An important feature of the described preferred embodiment is that the drive belt 106 has a resilient face or backing 110 effective to conform to and grip the contoured surface of the workpieces with uniform gripping force so that they can be fed into the grinder without breakage, even when there is a relatively large force overall.
1. A part drive assembly comprises a lower support for supporting workpieces (20)
to be fed into an adjacent station (16), an upper-part drive comprising a drive sprocket
(60) adapted to be power-driven in a predetermined rotary direction, a pair of longitudinally
arranged and spaced-apart pulleys (129,130) disposed immediately above the lower support
for the workpieces (20), an endless drive belt (106) operatively routed around the
drive sprocket (60) and the pulleys (129,130), the drive belt (106) having an outer
continuous backing (110) of resilient material which resiliently conforms to the contour
of the workpieces (20) to thereby grip workpieces (20) of varying size for feeding
the workpieces (20) across the lower support into the adjacent station (16).
2. A part drive assembly according to claim 1, characterised in that the lower support
is provided by a plurality of rollers (170) which fit along the inside surface of
the workpieces (20).
3. A part drive assembly according to claim 1, characterised in that an air-pressurised
hold-down assembly (142) is provided for the inner part of the drive belt (106) immediately
above the lower support, with variable-pressure means (150) for exerting a pressure
by way of the hold-down assembly (142), and the drive belt (106) is adapted to contact
and grip the upper portion of each of the workpieces (20) with a constant pressure
as they are fed along the lower support.
4. A part drive assembly according to claim 3, characterised in that a plurality of
rollers (160) are supported by an upper block (158) and contact the drive belt (106)
to provide a force on the drive belt (106) so that a portion of the belt (106) conforms
to the shape of the workpieces (20).
5. A part drive assembly acording to claim 1, characterised in that, for feeding a
train of the workpieces (20) into upper and lower grinding wheels (112,114), the drive
sprocket (60) of the upper-part drive comprises an upper drive sprocket, the outer
continuous backing (110) of the drive belt (106) comprises resilient foam material,
and the drive belt (106) with its continuous backing (110) of resilient foam material
is effective to grip each of the workpieces (20) with a substantially constant gripping
force for feeding the workpieces (20) across the lower support into the grinding wheels
(112,114).
6. A part drive assembly according to claim 5, characterised in that the lower support
is provided by a line of rollers (170) which fit along the inside surface of the workpieces
(20) to support the workpieces (20) from the bottom side thereof.
7. A part drive assembly according to claim 5, characterised in that an air-pressurised
hold-down assembly is provided for the inner part of the drive belt (106) immediately
above the lower support, and pressure means is provided for transmitting a pressure
by way of a support block (158) to the drive belt (106) so that the drive belt (106)
contacts the upper portion of the workpieces (20) with a constant gripping force.
8. A part drive system according to claim 7, characterised in that a line of rollers
(160) is supported by the support block (158) and contacts the drive belt (106) to
provide a force on the drive belt (106) such that the drive belt (106) conforms to
the shape of the workpieces (20) all along the drive surfaces thereof.
9. A method of force-feeding a plurality of substantially identical and contoured
workpieces (20) into a resistive force of a pair of opposed grinding wheels (112,114),
comprising loading the workpieces on a conveyor (12), actuating the conveyor (12)
so that it moves the workpieces (20) as a train on to a track (22) in a part drive
station (14), operating a drive belt (106) of the drive station (14) to grip the workpieces
(20) and serially move the workpieces (20) from the track (22), with resilient deformation
of at least an outer portion of the drive belt (106) to conform to and grip the contour
of the workpieces (20), and forcing the workpieces (20) in an abutting train between
the grinding wheels (112,114) by the action of the drive belt (106) so that the workpieces
(20) will be ground by the grinding wheels (112,114).