Belt Conveyor For Sheet Material

Abstract

A perforated conveyor belt for cardboard sheets and the like travels over a row of suction chambers sequentially evacuated in synchronization with the belt travel by a suction pump connected with the chambers through a rotary distributor valve in which the orifice of an exhaust conduit in the valve rotor sweeps circumferentially offset ports on the valve shell, the ports being connected to the chambers respectively. The circumferential width of the orifice may be adjusted for varying the number of simultaneously evacuated chambers. The valve rotor and the belt are driven synchronously by a common motor.

Description

This invention relates to a belt conveyor, and particularly to a conveyor for cardboard blanks and like pieces of sheet material which need to be held to the conveyor belt by suction.

When cardboard blanks are processed in a plurality of stages in the manufacture of cartons or the like by equipment consisting of individual units connected by transfer conveyors, it is often important to maintain precise alignment of the blanks with their direction of movement on the conveyor. It is usually preferred to employ belts in which perforations extend between the two major belt faces, and to move the belt over open chambers in which at least a partial vacuum is maintained by a suitable pump. It is not desirable to maintain such vacuum at all times. It is particularly undesirable to connect a chamber to the vacuum pump while the perforations in the belt are not covered by a conveyed sheet, and thus connect the chamber with the ambient atmosphere. It is not even desirable nor necessary in many instances to connect all chambers subjacent the traveling sheet with the pump since the power required for driving the belt and the wear-inducing contact pressure between belt and chambers increase with the number of evacuated chambers.

It has therefore been proposed to equip a conveyor of the type described with sensitive limit switches, relays, and solenoid valves. The limit switches sense the presence or absence of sheet material on the conveyor belt, and they are connected with solenoid valves in the vacuum lines to the individual chambers through relays to connect the vacuum pump only to selected chambers. Relay and solenoid coils cause a time lag between the actuation of the limit switch and the opening of the valve, which lag is unavoidable and not acceptable at very high conveyor speeds. Moreover, limit switches relay for operativeness on freedom from contaminants not always capable of being achieved under the conditions common in box manufacturing plants, and the known electrically operated vacuum controls for belt conveyors of the type described require relatively frequent preventive maintenance operations even if their relatively sluggish response is acceptable.

The object of the invention is the provision of a suction-type conveyor in which proper synchronization between the evacuation of the suction chambers and the movement of the conveyor belt is achieved at all practical conveyor speeds and with great reliability over extended periods of operation without requiring overhaul or other maintenance of the vacuum controls.

With this object and others in view, the invention provides a conveyor of the type described with a rotary valve interposed between the suction pump and the vacuum chambers under the conveyor belt which sequentially connect the pump to the chambers. A common drive motor is connected to the belt and to the valve for moving the belt in a closed loop and for sequentially connecting the chambers to the pump in timed sequence.

More specifically, the rotary valve includes an outer shell having an axis and formed with ports angularly distributed relative to the axis. conduits respectively connect the ports to the chambers, and a rotor mounted in the housing shell for rotation about the axis of the latter by the drive motor defines an exhaust conduit having two orifices of which one sequentially sweeps the ports during rotation while the other orifice is connected to the pump.

The performance characteristics of the vacuum system may be adapted to various conveyed materials by adjusting the circumferential width of the exhaust conduit orifice, and by thereby varying the number of simultaneously evacuated chambers.

Other features, additional objects, and many of the attendant advantages of this invention will readily be appreciated as the same becomes better understood by reference to the following detailed description of a preferred embodiment when considered in connection with the appended drawing in which:

FIG. 1 shows a conveyor of the invention in side elevation, and partly in section, and the associated pneumatic circuit in a conventional manner;

FIG. 2 illustrates a valve in the circuit of FIG. 1 in side elevational section;

FIGS. 3 and 4 are front elevational sections of the valve of FIG. 2 taken on the lines III--III and IV--IV respectively; and

FIG. 5 shows the valve of FIG. 2 in rear elevational section on the Line V--V.

Referring now to the drawing in detail, and initially to FIG. 1, there is seen an endless conveyor belt 10 trained over four pulleys 12. One of the pulleys 12 is driven by an electric motor 14 and draws the belt 10 horizontally over the open tops of a row of ten contiguously justaposed suction chambers 16. As is conventional in itself and not capable of pictorial representation on the scale of FIG. 1, the major faces of the belt 10 are connected by a multiplicity of perforations, and the orifices of the perforations in the bottom face of the belt communicate with the chambers 16 when traveling over the same.

The chambers 16 are sequentially connected with a vacuum pump 18 by two sections 20, 22 of a rotary distributor valve more fully illustrated in FIGS. 2 to 5, each section having five suction ports 24 respectively connected with associated chambers 16 by pipes 26. As indicated by a broken line, the valve sections 20, 22 are coupled to the motor 14 and the driven guide pulley 12 for synchronous operation.

The distributor valve, as shown in FIG. 2, has an outer cylindrical shell 28 fixedly mounted on the supporting frame 30 of the belt conveyor which also carries the pulleys 12 in a known manner, not shown. Axially spaced ball bearings 32 in the shell 28 support the valve rotor which includes a partly hollow shaft 34. The solid axial end portion of the shaft 34 is coupled to the motor 14 by a gear transmission 36 including bevel gears 38 on the shaft 34 and on the ouput shaft of the transmission whose input shaft is coupled to the motor 14 in an analogous manner.

Two flanged sleeves 40, 42 carry the inner races of the ball bearings 32 and are rotatably mounted on the shaft 34. The sleeve 40 on the solid end portion of the shaft 34 projects from the shell 28 and carries a clutch disc 44 axially slidable on the sleeve 40, but secured against rotation by a key 46. In the illustrated position, the disc 44 is held in driving connection with the flange 48 fixed on the shaft 34 by a fork 50 engaging a circumferential groove in the disc 44 in a manner not specifically shown but well known in clutch disengaging mechanisms of automotive friction clutches. The fork 50 is pivotally mounted on the frame 30 and operated by means of a double-acting hydraulic or pneumatic cylinder 52 which is also mounted on the frame 32 and manually controlled in a conventional manner, not shown.

A worm wheel 54 normally rotates freely on the sleeve 40 when a worm 55 journaled in the frame 30 is turned by means of a non-illustrated handwheel. The clutch disc 44 may be engaged with the worm wheel 54 by means of the cylinder 52, friction facings being provided on the axially opposite, radial engagement faces of the wheel 54, the disc 44, and the flange 48.

The tubular part of the shaft 34 has an internal annular shoulder 56 which separates an inner portion 58 of the bore in the shaft 34 from an outer, wider bore portion. A coaxial tube 60 fixedly sealed in the shoulder 56 and the wider, tubular, axial portion of the shaft 34 radially bound an annular conduit 62. The tube 60 axially projects beyond the shaft 34 through a cap 64 on the shell 28 and into a chamber 66. The tube 60 is slidably sealed in the cap 64 whose cavity 68 freely communicates with the conduit 62. Respective radial openings 70, 72 in the tubular portion of the shaft 34 connect the bore portion 58 and the conduit 62 with respective axial portions of the space between the shaft 34 and the shell 28 which are separated from each other by an annular disc-shaped partition 74. Suction lines 76, 78 respectively lead from the cavity 68 and the chamber 66 to the pump 18.

As is shown in FIGS. 3 and 4, two vanes 80, 82 are attached to the hollow portion of the shaft 34 by screws 84 on opposite axial sides of the partition 74. Two corresponding vanes 86, 88 are mounted on respective pairs of axial bolts 90 between the partition 74 and the flanges of the sleeves 40, 42 so that the flanges are axially connected by the bolts 90 and the partition 74 into a fixedly connected portion of the rotor which is normally coupled to the shaft 34 by the clutch disc 44 for joint rotation.

The rotor thus defines two exhaust conduits of which one extends from the suction line 78 through the chamber 66, the tube 60, the bore portion 58, the opening 70 to an orifice circumferentially bounded by the vanes 80, 86 and axially bounded by the flange of the sleeve 40 and the partition 74. The other exhaust conduit extends from the suction line 76 through the cavity 68, the annular conduit 62, the opening 72, to its orifice between the vanes 82, 88, the flanged sleeve 42 and the partition 74. The partition axially separates the two groups of five ports 24 of the respective valve sections 22, 22' arranged in the upper half of the cylindrical shell 28, the lower half being imperforate. The openings 70, 72 respectively associated with the valve sections and the associated orifices are offset 180.degree. relative to the axis of rotation of the shaft 34 so that the orifices of the two exhaust conduits sweep the ten ports 24 consecutively and at uniform intervals during each revolution of the shaft 34.

In the illustrated relative angular position of the vanes 80, 82, 86, 88 on the shaft 34 and between the flanged sleeves 40, 42, the orifices are wide enough only to connect one port 24 and the associated chamber 16 at one time to the pump 18, and the shaft 34 is synchronized with the pulleys 12 in such a manner that the belt 10 progresses at the same rate as the vacuum in the row of chambers 16. If a relatively light and stiff piece of cardboard 92 is presented to the conveyor as is indicated in FIG. 1 in phantom view, the front end of the piece, as viewed in the direction of belt movement, is attached to the belt 10 by the vacuum in a subjacent chamber 16 and travels thereafter with the belt, its front end being held in contact with the belt by the vacuum produced by the pump 18. The vacuum gradually decays by leakage in the chambers shut off from the pump by the rotary distribution valve, and the piece of cardboard is ultimately discharged from the conveyor belt 10 and free to be grasped by the feed mechanism of the next machine in the production line, not itself shown.

When blanks of relatively heavy or resilient material are to be conveyed on the belt 10, it may be desirable to secure them to the belt 10 by vacuum over much of their length, and the number of consecutive chambers 24 which are simultaneously held at the highest available vacuum can be adjusted by shifting the vanes 86, 88 circumferentially away from the vanes 80, 82. For this purpose, the motor 14 is stopped, the clutch disc 44 is disengaged from the flange 48 and engaged with the worm wheel 54, whereupon the latter is turned by means of the non-illustrated handwheel on the worm 55 until the desired orifice sizes of the two exhaust conduits are set. The setting is fixed by returning the clutch disc 44 to the illustrated position.

The valve arrangement illustrated and described has been found more reliable than the combination of limit switches and solenoid valves employed heretofore. Its initial performance is better at high conveying speeds than that of the best available electromagnetic systems, and its durability is very great since it is immune to contaminants and does not rely for operativeness on absolutely tight seals between the moving valve parts. It need not be built to extremely close tolerances, and is not subject to deterioration by wear over long periods.

The division of the rotary valve into two sections 20, 22 respectively controlled by the vanes 80, 86 and the vanes 82, 88 permits dynamic balancing of the valve rotor in a manner not readily achieved otherwise, and essential for high-speed operation.

It should be understood, of course, that the foregoing disclosure relates only to a preferred embodiment, and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.

Claims

What is claimed is:

1. A conveyor comprising, in combination:

a. a perforated, elongated, endless belt having two opposite major faces and being formed with a multiplicity of perforations connecting said faces;

b. guide means for longitudinally guiding said belt in a closed loop;

c. a row of stationary chambers contiguously adjacent one of said faces and open toward the perforations in said one face;

d. a suction pump;

e. rotary valve means operatively interposed between said pump and said chambers for sequentially connecting said pump to said chambers; and

f. common drive means connected to said belt and to said valve means for moving said belt in said loop and for sequentially connecting said chambers to said pump in timed sequence, said valve means including

1. an outer shell having an axis and formed with a plurality of ports angularly distributed relative to said axis, a plurality of conduits respectively connecting said ports to said chambers,

2. a rotor mounted in said shell for rotation about said axis by said drive means, said rotor defining an exhaust conduit having two orifices, one of said orifices sequentially sweeping said ports during said rotation, the other orifice being connected to said pump, said rotor having a radially inner portion and a radially outer portion carrying respecive vanes circumferentially bounding said one orifice,

3. means for angularly moving said outer portion relative to said inner portion about said axis, and for thereby varying the circumferential width of said one orifice,

4. clutch means normally coupling said outer portion to said inner portion for joint rotation, and

5. clutch disengaging means for disengaging said clutch means during said angular moving of said outer portion.