GB2111247A

GB2111247A - Method of and device for automatically correcting the offset between two endless conveyor belts conveying a set of pieces

Info

Publication number: GB2111247A
Application number: GB08231790A
Authority: GB
Inventors: Anna Bravin
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-11-16
Filing date: 1982-11-08
Publication date: 1983-06-29
Also published as: GB2111247B; FR2516488A1; IT8168486A0; IT1145734B; DE3241397A1; NL191559B; NL191559C; CH651804A5; NL8301725A; FR2516488B1

Abstract

The arrival of a product piece (2) onto an upstream belt (4), is used to initiate the storing of a digital signal representing the position of a downstream belt 17, having recesses for receiving product pieces. The output of the store (11) is connected to an input of an adder (13), the second input of which is connected to an up-down counter (14) fed by pulses from a detector (12) coupled to the belt (4), the output of the adder, through a D/A converter (16) controls the position of the upstream belt so that the delivery of product pieces from the upstream belt is such that the recesses of the downstream belt are filled. <IMAGE>

Description

SPECIFICATION Method of and device for automatically correcting the offset between two endless conveyor belts conveying a set of pieces The present invention relates to a method of automatically correcting the offset between two endless conveyor belts conveying a set of product pieces which are identical or have at least the same length and to a device for carrying out the method.

The method may be used in several industrial fields; but for sake of simplicity reference will be made to a packing machine and to the corresponding feeding group.

That group consists of a chain of conveyor belts, arranged one after the other, which receive mutually contacting product pieces, suitably space apart and supply them to a belt provided with equally spaced, outward projecting transversal teeth, defining a continuous succession of recesses each receiving a product piece and delivering it to the packing machine. Said belt moves at a speed dictated by the packing machine, while the feeding belts and particularly the one on which the products are spaced apart are driven by their own motors.

It is easy to understand that, while thousands of cycles are carried out, the speed ratio may vary thereby creating problems. In effect, in the event of a lead in the arrival of a piece, the recess is still occupied and the piece cannot be received. It can therefore fall down and become deteriorated. In case of a lag in the arrival, the piece is not in time to occupy the recess which then remains empty.

Therefore, the packing machine makes one or two operations in vain, wasting the packing material.

It is an object of the invention to eliminate these drawbacks by acting on the member driving the spacing belt, by increasing or decreasing its speed.

The method of the invention consists in detecting the arrival of a product piece on a first belt (upstream belt), generating a pulse train representing the position of the second belt (downstream belt), storing the position of the downstream belt whenever the arrival of product onto the upstream belt is detected, converting the stored value into an error signal which is fed to members controlling a motor associated with the upstream belt to cause or adjust the movement thereof, and generating at each intervention on said motor feedback signals in order to annul the error signal when the offset between the two belts has been corrected.

The error signal may be obtained by converting into analog form and subsequently amplifying a signal obtained as the algebraic sum of the stored value and of the output signal of an up-down counter which counts forward the pulses representing the position of the second belt and backward the feedback signals. As an alternative, the error signal may be the signal generated by a discriminator on the basis of the stored value.

The error signal may directly act on the control members of the motor driving the upstream belt, which members also receive a signal representing the speed of the downstream belt. According to an embodiment in which the upstream belt is driven by the downstream belt through a differential gear, the error signal may start a motor connected with the shaft of a bell member carrying the planet gears of the differential.

The feedback signal may be signals representing the angular position of the motor driving the belt or the bell: when the bell is driven by a step-by-step motor receiving as error signal the signals generated by the discriminator, the same signal may form the feedback pulses.

The device for carrying out the method comprises a detector of the arrival of a product piece onto the upstream belt; a first pulse generator which generates digital signals representing the position of the downstream belt; a memory device for storing the signals emitted by the first pulse generator whenever the arrival of a product piece on the upstream belt is detected; means for obtaining from the stored value an error signal which is fed to means for driving a motor associated with the upstream belt to cause or adjust the movement thereof; and means for generating, whenever the upstream belt motion is varied, feedback signals intended to annul said error signal when the offset between the two belts has been corrected.

The invention will be better explained with reference to the accompanying drawings, which schematically show three possible embodiments of the invention.

In Fig. 1, a first conveyor belt 1 conveys mutually contacting product pieces 2, which the belt receives from a manufacturing station. The pieces are spaced apart by one or more other conveyor belts, for instance two belts 3, 4 driven by a motor 5, which in the embodiment of Fig. 1 is a low-inertia d.c. motor. Belt 4 is followed by a further belt 6 which is to forward the product pieces to a feeding belt 7 for the packing machine or for another machine which is to handle individual pieces.

The surface of belt 7 has equally spaced transverse teeth 8 which define on the surface itself recesses intended to receive each a product piece 2. Belt 7 is exactly synchronized with the packing machine, of which only motor 9 is shown.

In order to speed up the transport from the manufacturing station to the packing one, the speed of belt 4 will be higher than, for instance a multiple, of that of belt. The two speeds will have to be rigidly linked in order to prevent recesses in belt 7 from remaining empty, with consequent waste of the packing material, or to prevent a piece 2 from arriving at a recess already occupied, whereby it cannot be received by belt 7.

The invention aims to recover the possible offset between belts 4 and 7.

To this end, a photoelectric cell 10, or another device apt to detect the arrival of a piece 2, is arranged adjacent belt 4. The output signal of that detector is a control signal for a memory 11 which stores a digital signal generated by a device 12, of known type, detecting the angular position of the shaft of motor 9 of the packing machine.

Device 12 is connected to the motor driving belt 7, in such a manner that every step of conveyor belt 7 bringing a recess to a position suitable for receiving a piece 2, corresponds to a revolution or a fraction of a revolution of the detector. The output of memory 11 is connected to a first input of an adder 13, a second input of which is connected to the output of an up-down counter 14, which counts forward the signals issued by detector 12 and backward the signals issued by a second position detector 15, associated with motor 5, The output of adder 1 3 is connected to a digital-to-analog converter 1 6 followed by an amplifier 17, in turn connected to the control members 1 8 of motor 5.In these members, the output voltage of amplifier 17, which is an error signal representative of the offset between the motors, is algebraically added to a voltage representation of the speed of motor 9, which voltage is picked up by a suitable device 1 9. Thus, if the error voltage is not 0, the desired variation of the speed of belt 4 will be obtained. Through pulse generator 15, counter 14 and adder 13, the error signal will be brought to 0 when the offset has been corrected.

In the embodiment shown in Fig. 2, belt 4 is driven by motor 9 through a differential gear 20, the planet gears of which are carried by a bell member 21 which can be rotated by a low inertia d.c. motor 22; the control circuits 23 of said motor are driven by error signal supplied by amplifier 1 7.

Detector 1 5 is associated with the shaft of motor 22.

By this arrangement, motor 22 and hence bell 21 will remain stationary until an offset between the speeds of the two belts occurs; afterwards motor 22 is rotated in one direction or the other until the number of pulses generated by detector 1 5 annuls the output signal of the adder.

In the embodiment of Fig. 3, conveyor belt 4 is still driven by the motor 9 of the packing machine through differential gear 20, identical to that of Fig. 2. In this case however bell 21 is mounted on the shaft of a step-by-step motor. Control members 25 of that motor are connected to a discriminator 26 having two outputs, one output or the other being actuated according to whether the motor is to be moved forward or backward.

Discriminator 26 operates on the ground of the angular position of conveyor 7, stored in memory 11. That memory is also associated with a counter having a positive and a negative input connected to the corresponding discriminator Outputs, to reset the memory after the correction.

If desired, the memory can be reset by a pulse generator similar to generator 1 5 of Fig. 2 and associated with step-by-step motor 24, instead of being reset by the output signals of discriminator 26. That generator is however necessary only if the response time of step-by-step motor 24 is critical for the operation. If the reaction time leaves a sufficient margin of safety, the reset pulses for the memory can be the pulses sent to the step-by-step motor, as the displacement of the motor at each step is known.

It is evident that the above description is given only by way of non limitative example, and that changes and modifications are possible without departing from the scope of the invention defined by the appended claims.

Claims

1. A method of automatically correcting offset between two endless conveyor belts conveying a set of product pieces, comprising detecting the arrival of a product piece onto the first belt, generating a pulse train representing the angular position of the second belt which is arranged downstream of the first and belt which is driven by a motor of a machine to which the pieces are delivered, storing the position of the downstream belt, converting the stored value into an error signal, sending said error signal to control drive members associated with the upstream belt and causing or adjusting the motion thereof, and generating at each correction of the motion of the upstream belt feedback signals in order to annul the error signal when the offset has been corrected.

2. A method according to claim 1, in which the error signal is generated by converting into analog form and amplifying a signal obtained as an algebraic sum of the value stored and of the output signal of a counter which counts forward and pulses representing the position of the second belt and backward the feedback signals.

3. A method according to claim 2, in which said error signal is sent to the control members of a motor driving the upstream belt, and is algebraically added to a signal representing the speed of the downstream belt.

4. A method according to claim 2, in which said error signal is sent to a motor for adjusting the speed of the upstream belt and which acts on members transmitting the motion of the downstream belt to the upstream belt.

5. A method according to claim 1, in which said error signal is the output signal of a discriminator which, in response to the value stored, generates pulses for moving forward or backward a step-bystep motor for adjusting the speed of the upstream belt and acting on members transmitting the motion of the downstream belt on the upstream belt.

6. A method according to any of claims 1 to 5.

in which said feedback signals are pulses representing the position of the motor driving the upstream belt or adjusting the speed thereof.

7. A method according to any of claims 1 to 5, in which said feedback pulses are the output signals of the discriminator.

8. A device for carrying out the method according to any of claims 1 to 7, comprising a detector for detecting the arrival of a product piece onto the upstream belt; a first pulse generator arranged to digital signals representing the position of the downstream belt; a memory unit, which stores the signal emitted by the first pulse generator upon command of a signal emitted by said detector and indicating the arrival of a product piece onto the upstream belt; means for obtaining from the signal stored an error signal and for sending said error signal to members which causes or adjust the motion of the upstream belt; and means for generating, at each correction of the motion of the first belt feedback signals intended to annul said error signal once the offset between the two belts has been corrected.

8. A device for carrying out the method according to any of claims 1 to 7, comprising a detector for detecting the arrival of a product piece onto the upstream belt; a first pulse generator arranged to digital signals representing the position of the downstream belt; a memory unit, which stores the signal emitted by the first pulse generator upon command of a signal emitted by said detector and indicating the arrival of a product piece onto the upstream belt; means for obtaining from the signal stored an error signal and for sending said error signal to members which cause adjusts the motion of the upstream belt; and means for generating, at each correction of the motion of the first belt feedback signals intended to annul said error signal once the offset between the two belts has been corrected.

9. A device according to claim 8, including an up-down counter in which the input for the forward counter is connected to said first pulse generator, the input for the backward counting is connected to the means generating the feedback signals and the output is connected to a first input of an adder receiving at a second input the stored signal and calculating the difference between the input signals, said adder being connected to a digital-to-analog converter followed by an amplifier whose output voltage is said error signal.

10. A device according to claim 9, in which the output of said amplifier is connected to control members of a motor driving the upstream belt and in that means are provided for generating and sending to said control members a signal representing the speed of the downstream belt.

11. A device according to claim 9, in which the output of said amplifier is connected to control members of a motor connected to the shaft of a bell member carrying the planets of a differential gear which transmits the motion of the downstream belt to the upstream belt, said motor being moved in either direction by the possible signal error.

12. A device according to claim 9, including a discriminator having an input connected to the memory output and two outputs connected to the control members of a step-by-step motor connected to the axis of a bell supporting the planets of a differential gear transmitting the motion of the downstream belt to the upstream belt, said motor being moved forward or backward depending on which output of the descriminator is actuated.

13. A device according to any of claims 8 to 12, in which the means for generating the feedback pulses comprises a second pulse generator which generates signals representing the positions of the motors driving the belt or respectively the bell, the output of said generator being connected to the input of said counter relative to the backward counting.

14. A device according to any of claims 8 to 12, in which the means for generating the feedback pulses comprises the discriminator itself, the outputs of which are connected to control inputs of which are connected to control inputs of an updown counter associated with the memory.

1 5. A method of automatically correcting the offset between two endless belts substantially as described herein with reference to Fig. 1, 2 or 3 of the accompanying drawings.

1 6. A device for automatically correcting the offset between two endless belts constructed and arranged substantially as described herein with reference to Fig. 1, 2 or 3 of the accompanying drawings.

New claims or amendments to claims filed on 24/2/83.

Superseded claims 1,2, and 8. New or amended claims:

1. A method of automatically correcting offset between two endless conveyor belts conveying a set of product pieces, comprising detecting the arrival of a product piece onto the first belt, generating a pulse train representing the angular position of the second belt which is arranged downstream of the first belt which is driven by a motor of a machine to which the pieces are delivered, storing the position of the downstream belt, converting the stored value into an error signal, sending said error signal to control drive members associated with the upstream belt and causing or adjusting the motion thereof, and generating at each correction of the motion of the upstream belt feedback signals in order to annul the error signal when the offset has been corrected.

2. A method according to claim 1, in which the error signal is generated by converting into analog form and amplifying a signal obtained as an algebraic sum of the value stored and of the output signal of a counter which counts forward the pulses representing the position of the second belt and backward the feedback signals.