Grinding Machine With Belts

Abstract

A belt grinding machine, including a workpiece conveyor mechanism, an endless grinding belt circulating above the conveyor transversely or longitudinally of the direction of movement of the workpiece, a resilient pressure member, associated with the said grinding belt to move and hold the grinding belt against the surface of a workpiece to be ground, a plurality of double acting pressure medium-operated cylinders and pistons arranged at intervals in the direction of the grinding movement of the belt, wherein each pressure medium operated cylinder is secured by its piston rod directly to the pressure member and is provided with a duct feeding a pressure medium moving the piston to a raised position of the grinding belt, and a duct feeding a medium for moving the piston to a working position of the grinding belt, and a control valve feeding the medium for the grinding pressure to the cylinder against the lifting pressure, or evacuating the medium from the cylinder, inserted in the duct supply medium effecting the raised position of the grinding belt, said valve being connected to a senser actuating a switching and control device in dependence on the presence of a workpiece, and a timing relay operated by the said switching and control device to operate the control valve.

Description

PRIOR APPLICATION

In Germany on May 9, 1972 and numbered P 22 22 616.0.

The present invention concerns a grinding machine with means for conveying workpieces therethrough. The machine comprises a conveyor mechanism including belts, chains or the like moving the workpieces to be ground, an endless grinding belt circulating transversely or longitudinally with respect to the direction of movement of the workpieces and located above the conveyor mechanism, and a resilient pressure member associated with this grinding belt to urge it against the surface of the workpieces to be ground. The said member includes a plurality of double acting cylinders operated by a pressure medium and arranged at adjacent spaced intervals along the direction of movement of the grinding belt.

Such belt grinding machines which are known in various forms more particularly for grindng flat workpieces having regular or irregular shapes, are usually provided, with a complicated and expensive mechanical control device for moving the grinding belt towards the workpieces to be ground and away from the workpieces to an inoperative position. In spite of this complication, these machines do not give perfect grinding results, particularly in the case of somewhat uneven workpiece surfaces.

It is an object of the present invention to improve a belt grinding machine of the type described and to provide it with a control means for moving a pressure member which is simply and economically designed and which operates reliably independently of the movement and shape of the workpiece, for a pressure member moving the workpiece into the grinding position and inoperative position respectively.

In a further object of the present invention, the belt grinding machine is to be constructed with a simply designed and reliably operating pulse transmitter for parts which move the grinding belt.

Furthermore, the grinding belt is to be moved by simple, reliable and smoothly operating means positively controlled in its type of movement by the configuration of the workpiece.

A further object resides in the simple, economical and durable construction of a grinding belt support enabling the operative surface of the grinding belt to be adapted to the surface of the workpiece to be ground.

In addition, individual parts or all of the grinding surface of the belt are to be reliably moved to the grinding position in accordance with the surface of the workpiece.

A further object is seen in the provision of grinding belt pressure elements rendering possible grinding of both plane and uneven workpiece surfaces.

According to the present invention there is provided a belt grinding machine, including a workpiece conveyor mechanism, an endless grinding belt circulating above said conveyor mechanism in a direction selected from transversely and longitudinally of the direction of movement of the workpiece, a resilient pressure member associated with the said grinding belt, moving and holding the grinding belt against the surface of the workpiece to be ground, a plurality of double-acting pressure medium-operated cylinders and pistons arranged at spaced intervals in the direction of the grinding movement of the belt, each said cylinder, secured by its piston rod directly to said pressure member, is provided with a duct feeding a pressure medium to move the piston to a raised position of the grinding belt and a duct feeding a medium to move the piston to a working position of the grinding belt, a control valve which feeds the medium for the grinding pressure to said cylinder against the lifting pressure, or evacuates it from said cylinder is interposed in said duct effecting the raised position of the grinding belt and is connected by means of an electrical switching and control device to a time relay adjustable in dependence on the presence of a workpiece to a scanning member actuating said switching and control device.

According to the present invention there is also provided a belt grinding machine wherein the two actuated piston surfaces of the piston vertically reciprocated at right angles to the plane of movement of the workpiece, of each said cylinder are connected by way of said duct each to a pressure medium chamber extending over all adjacent said cylinders, preferably a closed pipe sealed at the ends, and, from the lower pressure medium pipe of the two superimposed said pipes, a medium is fed continuously loading the lower actuating surface of said piston and holding or bringing it in a lifted position and from the upper pipe a medium is fed, greater in pressure, loading the upper piston surface and bringing said piston into a working position dependent on the movement of the workpiece, whilst a valve, preferably a magnetic valve, is inserted in said pressure medium duct for the pressure movement, said valve being controllable dependently on the workpiece, wherein the said control valve associated with each said cylinder is connected by way of an adjustable switching and control device, preferably a time-relay, with a contact switch which holds on a contact lever, a sensing member formed by a roller or the like and actuated by the moving workpiece, wherein supporting brackets are secured to extension arms of the machine chassis, which brackets support on their rear side, in the direction of movement of the workpiece, said superimposed pipes with the said cylinders secured thereto, and the said control valve disposed thereon, and carry, on the front side, in the direction of movement of the workpiece, said contact switches on a vertically adjustable holding rail, wherein the piston rod of each said cylinder is directly secured to a cross-bar of a resilient pressure member preferably formed by an air cushion pressure beam.

A belt grinding machine of the present invention is fitted with control means for the respective operating and resting positions of the grinding belt, which control means presses the grinding belt against a workpiece surface to be ground and lifts it from the workpiece when the grinding process is finished.

The pressure member holding the grinding belt against the workpiece is moved by means of hydraulic cylinders under control of means for sensing the pressure of the workpiece. Electrical switching and control devices are actuated so that the resilient pressure member only adapts itself to the surface of the workpiece, its capacity to do so being improved by providing separate movement of each individual cylinder. The pressure member is thus moved flexibly against the workpiece by the individual cylinders, with the result that any irregularities in the surface of the workpiece are compensated.

The same pressure is exerted on each piston of the cylinders, and since each piston can effect a certain stroke, compensation for tolerances in the workpiece surface is possible within this range; one piston may extend further than another in the direction of the workpiece surface and thus individual portions of the grinding belt are brought by the pressure member into contact with the workpiece surface to be ground.

Each hydraulic cylinder is controlled by its own sensing member which senses the edge of the workpiece and then initiates the pressure movement of the driving belt with a delayed action. In order that the edges of the workpieces can be perfectly ground and grinding errors avoided, adjacent cylinders can be moved independently of each other by one or more sensing members and one or more coordinated electrical switching and control devices.

The control means is economically designed by the avoidance of complicated mechanical means and the provision of time relays as switching and control devices, and is greatly improved in its operation compared with conventional control means.

An embodiment of the present invention is illustrated in the accompanying drawings, in which:

FIG. 1 is a perspective view of a belt grinding machine of the present invention;

FIG. 2 is a side view in partial section of the pressure member;

FIG. 3 is a plan view of the pressure member arranged above the conveyor; and

FIG. 4 is a front view of the pressure member showing the pressure operated cylinders.

A belt grinding machine according to the present invention for grinding regularly or irregularly shaped plate-like workpieces 10, which may have an even or somewhat uneven surface, has a machine frame 11, a motor-driven conveyor 12, shown as including endless belts, the conveyor moving the workpieces 10 to be ground, in a continuous process. Above this conveyor 12 is mounted an endless grinding belt 13 which circulates transversely to the direction of movement of the workpieces and is motor-driven independently of the conveyor 12. The belt is held against the workpiece 10 in the grinding position by a resilient pressure member 14, extending substantially over the lower length of the grinding belt 13 between its two guide pulleys 15, or between guide pulleys 49 of a laminated pressure belt 48.

This pressure member 14 has a plurality of fluid pressure operated cylinders 16 which are arranged adjacent each other at uniformly spaced intervals along the direction of movement of the grinding belt and effect a movement of the pressure member 14 into a grinding position (the grinding belt 13 is pressed against the workpiece surface to be ground) or into a raised position (no grinding contact between grinding belt 13 and workpiece surface).

Each cylinder 16 is attached to the pressure member 14 by its piston rod 17 which is displaceable at right angles to the plane of movement of the workpiece; this piston rod 17 is actuated by a double-acting piston 18 in cylinder 16 which may be displaced backward or forward by a pressurised fluid, preferably air, though it may also be oil or other liquid. This moves the pressure member 14 into a resting or operative position.

Each cylinder 16 is provided with ducts feeding the pressure medium to produce a raised or working position of the grinding belt. In the duct producing the working position of the grinding belt is inserted a control valve 19 which supplies the medium for applying grinding pressure to the pressure operated cylinder 16 or evacuates it from the cylinder. The valve is actuated by a relay 20 and a senser 21.

The cylinder space of each pressure operated cylinder 16 is divided into two chambers 22, 23 by double acting piston 18. It is provided, near the chamber 22 adjacent to the pressure member 14, with a duct 25 connecting this chamber 22 to a pressure medium chamber 24, and near its chamber 23 with a duct 26 which connects the chamber 23 to a pressure medium chamber 27 and the control valve 19.

The two pressure medium chambers 24, 27 are separated from each other and extend across all the pressure operated cylinders. These two pressure medium chambers are of rectangular cross section, the depth of which corresponds to the length of each cylinder.

Two spaced apart supporting brackets 28 are disposed on extension arms 11a on the machine chassis 11 above the grinding belt 13. They carry on their rear sides the two superimposed chambers 24, 27 and on their front sides, a support member 29 on which the sensers are mounted.

The housing 30 of each pressure medium cylinder 16 is provided at its lower end with a projecting piston rod 17, displaceable in a vertical plane and, at its upper end, carries the control valve 19. Near each pressure medium cylinder 16, each chamber 24, 27 is traversed by a connecting means, preferably a bolt 31, 32 which acts to keep the cylinders 16 in contact with the chambers 24, 27 and thus with the holding brackets 28, and also effects a flow path between the chambers 24, 27 and respective ducts 25, 26. For this purpose each bolt 31, 32 provided with an axial blind bore 33, 34 extending in the longitudinal direction of the bolt, the bores being connected to the chambers 24, 27 by several transverse bores 35, 36 formed in the portion of the bolts extending within the chambers 24, 27.

Each of the two bolts 31, 32 for each pressure medium cylinder 16 screws into the housing 30 of the cylinders and the ducts 33, 34 then communicate with the ducts 25, 26 of the housing 30. The duct 25 is an angle member which is connected with the bolt duct 33 and terminates in the bottom of the chamber 22.

The duct 26 is composed of two parts, angled part connected to the bolt duct 34 and communicating with the control valve 19 and a part extending from the control valve 19 and terminating in the bottom of the housing opposed to the angled duct 25.

The scanning member 21 is a scanning roller journalled to rotate on a switching lever 37a of a contact switch 37. The contact switches 37 are mounted with the interposition of spacers 38, on a vertically adjustable supporting rail 39 which is secured by means of the spacers 38 to the support member 29. Each contact switch 37 is connected by an electrical lead 40 to a switching and control device 20 and each switching and control device 20 is connected by an electrical lead 41 to the control valve 19 whch is electro-magnetically operated.

A control valve 19 is associated with each pressure medium cylinder 16, senser 21 is provided with a contact switch 37 and a time delay relay 20, and each pressure medium cylinder and piston is actuated independently of the other cylinders.

Alternatively a scanning member 21 with contact switch 37 and a time relay 20 is provided in common to several pressure medium cylinders 16 so that the control valves of several cylinders are controlled by one scanning member 21.

The two chambers 24, 27, as supply means for all the cylinders 16, are each connected by a pipe with a pressure reducing valve, to a pressure medium supply.

In the chamber 24 there is always a pressure medium which transmits its force through the bores 35, the duct 33 and the duct 25 in the housing 30 to the chamber 22 so that there is always a pressure medium in the chamber 22 acting on the underside of each piston 18. If there is no workpiece 10 passing through the machine, the contact roller 21 is not actuated and the control valve 19 is not operated, so that the pressure medium (compressed air) in the chamber 22 displaces the piston 18 into a resting position, the pressure member 14 being in the upper resting position. The piston 18 is held against a stop 30a of housing 30 in this resting position by the compressed air. When a workpiece 10 passes into the machine to be ground, it presses the scanning roller 21, adjusted to a point somewhat lower than the upper edge of the workpiece, in the direction of the pressure member 14 so that the contact switch 37 is operated by the switch lever 37a. After a time which is previously set on the time delay relay 20, and which corresponds to time taken by the front edge of the workpiece to move to approximately the centre of the pressure member 14, the control valve 19 is operated so that the pressure medium reaching the control valve 19 from the chamber 27 through the bores 36, the duct 34 and the angle duct 26, can now flow through the control valve and enter the upper chamber 23 through the straight duct 26. The pressure of this medium is greater than the pressure of the medium in the chamber 22 and this forces the piston 18 into a working position in which the pressure member 14 holds the grinding belt 13 against the surface of the workpiece to be ground.

The lowest position of the piston 18 is determined by a stop 30b on the housing 30.

When the rear edge of the moving workpiece 10 releases the scanning roller 21, this roller returns to its original position and opens the contact switch 37; after a time previously set on the timing relay which corresponds to the time taken by the rear edge of the workpiece to move from the roller 21 to approximately the centre of the pressure member 14, the magnetic valve 19 is released and the chamber 25 above the piston 18 is evacuated by the valve 19.

The pressure of the medium in the chamber 22 then returns the piston 18 and the pressure member 14 to the upper resting position.

The resilient pressure member 14 is formed as a beam which has a cross bar 42 which is secured to the piston rods 17 and on which two spaced apart steel plates 24 are mounted by bolts 43. An air cushion 45 is located between the plates. A felt mat 46 is secured below the lower steel plate 44 by cementing the lower side (the side adjacent the grinding belt 13,) is covered by a sliding mat 47 secured at one end to the pressure member 14 and held at the other end with adjustable tension by a tensioning device.

This pressure member 14 formed in such manner can act by its sliding mat 47 on the grinding belt 13 or bear against the grinding belt 13 with the interposition of an endless circulating laminated pressure belt 48.

The air pressure in the air cushion 45 of the pressure member 14 corresponds to the pressure of the grinding belt 13 so that any tolerances (unevenesses) in the surface of the workpiece can be compensated by the elastic construction of the pressure member 14 within the air cushion 45.

Due to the large number of pressure operated cylinders 16 and scanning members 21 associated therewith, individual portions of various widths and shapes of the workpieces 10 passing through are scanned and then the pressure operated cylinders 16 are actuated. Each piston 18 has a certain stroke so that unevenesses in the workpiece surface are compensated by strokes of the pistons 18 of different length and the grinding belt 13 rests, due to the pistons 18, on the complete surface of the workpiece to grind it.

FIG. 4 of the drawings shows the grinding of a hollow round workpiece surface; the pistons 18, due to the contact pressure are displaced downwardly to a varying extent, the pistons 18 being lowered in their lowest position to the portion of the surface which is deepest and the pistons lowered to a portion of the surface which is not so deep being lowered to a lesser extent.

Individual portions of the pressure member 14 are moved more or less downwardly by the pressure operated cylinders 16 so that the grinding belt 13 is always completely in contact with the surface of the workpiece to be ground, thus any uneven surfaces are ground and tolerances in the surface of the workpiece compensated.

The pressure of all the pressure operated cylinders 16 is the same over the pressure member 14, only individual portions of the pressure member are pressed further down against the workpiece 10 according to the surface of said workpiece. By a fine adjustment of grinding pressure and counter-pressure it is possible for the piston 18 to float between the upper and lower end position (30a, 30b) so that comparatively large workpiece tolerances can be compensated in this manner, this compensation of tolerances being also assumed by the elastic pressure member 14.

It is preferable to use relays 20 having five poles and accommodated in the switch cabinet 50 so that not only the contact switches directly operated by the workpiece 10 and hence the associated cylinders 16 are operated, but also a plurality of adjacently disposed cylinders 16; this ensures that the edges of the workpieces are also exactly ground.

It is also within the scope of the present invention to provide more or less than five pole relays if the switching and control device 20 requires this.

In a special switching arrangement two or more groups of pressure operated cylinders may be combined so that they are controlled by respective scanning members. This enables a double or multi-track feeding of the machine to be possible in the grinding of regularly shaped workpieces.

Claims

What is claimed is:

1. A belt grinding machine comprising a grinding belt, a flexible pressure member for pressing an operative portion of said belt from a normally maintained inactive position downwardly against a workpiece conveyed in a first direction beneath said operative portion of said belt, said pressure member extending transversely of said first direction entirely across the width of the surface of the workpiece to be ground, a plurality of double acting, fluid pressure motors each having a first and a second internal chamber divided from each other by a piston having a rod projecting from the first chamber end of sad motor, the rods of said motors being connected to said pressure member at spaced locations transversely of said first direction and operable upon actuation of the associated motor to raise or lower the section of said pressure member connected thereto, a first pressure source commonly connected to all of said first chambers to urge said pistons and the connected pressure member toward a position of maximum elevation wherein said grinding belt is in said inactive position, a second pressure source maintained at a pressure higher than that of said first source, valve means on each motor operable to selectively connect the second chamber of the motor to said second source or to vent, and delayed action control means associated with each motor engageable with a workpiece surface at a location upstream of the direction of movement of the workpiece from each motor for actuating said valve means to position the grinding belt beneath the associated motor at a position corresponding to the position of the control means when the engaged portion of the workpiece subsequently arrives in operative relationship with the grinding belt.

2. A machine as defined in claim 1 wherein each of said pressure sources comprises an elongate tank extending transversely of said motors and fixedly secured to each of said motors.

3. A machine as defined in claim 2 wherein each of said motors has a first passage communicating with said first chamber and a second passage communicating with its valve means, first and second bolt means fixedly securing said first and second tanks respectively to said motors, said bolt means being respectively received in said first and second passages and placing said passages respectively in fluid communication with said first and second tanks.

4. A machine as defined in claim 3 wherein each of said bolt means comprises a shank having a threaded end threadably received in the motor passage, means defining an axial bore in said shank extending from the threaded end partially the length of the bolt, and a cross bore intersecting the axial bore establishing communication between the axial bore and the interior of the tank.

5. A machine as defined in claim 4 wherein said first passage opens into said first chamber at the end from which said rod projects and said second passage communicates with said valve means, each motor having a third passage extending from its valve means into said second chamber at the end of said second chamber remote from said rod.

6. A machine as defined in claim 5 further comprising stop means in each motor establishing opposite end limits of movement of its piston.