GB2128955A - Roller conveyor - Google Patents

Abstract

A driven roller conveyor is characterised in that it comprises a plurality of separately driven sections (2, 3), individually provided with: driving means (25) for driving rollers (1) such that an item is transported along the section; means (6, 6') for moving to driving means (25) whereby the driving means (25) can be engaged and disengaged from the rollers (1) so that the rollers (1) are selectively driven and free to rotate, and a first sensor means (21) is provided at the upstream end of each section and a second sensor means (21) at the downstream end of each section, said second sensor means (21) being arranged to activate the deactuation means (6) to disengage the drive means for that section on being contacted by an item, said first sensor means (21) being arranged to prepare the second sensor means on the preceding section for disengagement when said first sensor means is contacted by an item, whereby the drive to the preceding section is disengaged by the next succeeding item to contact said preceding second sensor means. <IMAGE>

Description

SPECIFICATION Conveyor This invention relates to driven roller conveyors and to a method for preventing accumulation of items on the conveyor.

The problem of accumulation of items on driven roller conveyors is well known in the art and has been met by a number of solutions. One commonly used mechanism involves a system whereby the drive to the driven rollers is allowed to "slip" when a build-up of items occurs. This system relies on the inertia of a relatively heavy item and the lack of free rotation of the rollers from which the drive is at least partially disengaged. Such a system thus works well in conditions where, for example, heavy crates or packing cases are being moved along a conveyor, such articles being both relatively heavy and tough.

A particular problem arises where the items to be transported along the conveyor are relatively light and subject to spoilage if they are moved over rollers which do not freely rotate. An example of such an item is the highly polished cabinet of a television set which, for ease of assembly, must be transported upside down, i.e. resting with the polished top surface in contact with the rollers. In such circumstances, any sudden stoppage of the rollers causes unacceptable scratching of the polished surface, which could only be avoided by the labour intensive (and hence expensive) use of separate protective pallets or mats. Another problem of such systems is that the transported articles are often allowed to jostle one another, which is again undesirable and causes scratching when articles such as television sets are transported.

We have now devised a driven roller conveyor on which lightweight articles or other articles having a delicate surface can be maintained at pre-set spacings and can be stopped without damage to the surface in contact with the conveyor.

According to the invention there is provided a driven roller conveyor for transporting items, characterised in that it comprises a plurality of separately driven sections, each section being individually provided with: driving means for driving rollers so that an item is transported along the section; means for bodily shifting the driving means, whereby the driving means can be engaged with and disengaged from the rollers so that the rollers are selectively driven or are free to rotate; and a first sensor means at the upstream end and a second sensor means at the downstream end of each section, said second sensor means being arranged to activate the deactuation means to disengage the drive means for that section on sensing an item, said first sensor means arranged to activate the second sensor means on the preceding section when said first sensor means senses an item, whereby the drive to the preceding section is disengaged by the next succeeding item to be sensed by said preceding second sensor means.

In general, the driving means used to propel some or all of the rollers in each section may be any convenient means which can be substantially instantaneously disengaged. One driving means comprises a friction drive wheel which can be moved to contact a roller.

Secondary drive means may also be provided by means of an auxiliary drive wheel arranged to contact said first driven roller so as to be driven thereby, and arranged to contact a subsequent roller. In this way trains of "slave" driven rollers can be provided, although it is usually undesirable to extend the drive through many stages because of the poor transmission of power. An alternative to a drive wheel is a toothed wheel gear system or the like. In a preferred form to drive means comprises a drive belt tensioned so as to run over pulleys mounted in a pivoted frame actuated by a ram to move between positions in which the belt is engaged with and disengaged from the rollers.

It is important that the rollers, both driven and free, are freely rotatable so as to provide the minimum of rolling resistance to the transported items. The rollers are preferably constructed of or covered with a suitably nonabrasive material, such as a smooth plastics composition.

It will be understood that the sensor means in each section work in cooperation with each other and with the sensor means in the next preceding section. The sensor means may in each case comprise any of a variety of suitable means, for example pressure-sensitive micro-switches, interrupted-ray switches and switches which react to a change in environmental impedance.

The means by which the first sensor means activates the second sensor means on the preceding section can be any conventional system, whether mechanical, electrical, or electronic. It is preferred that the sensor means shouid operate to generate electrical signals without contacting the items being conveyed. In its simplest form, the first sensor can actuate the second sensor on the preced ing section simply by acting as a relay to switch it on, but more sophisticated methods may be desirable involving the use of electronic micro-processor control.

It will be seen that it is not essential for the first sensor means to be controlled by the second sensor means in each section, although this is the case in a preferred embodiment of the invention.

The mode of operation is best considered with reference to a terminal section of the conveyor. an item arrives at such a section from the preceding section and is driven towards the end of the section where it contacts the second sensor means. This contact actuates the deactuation means which intantaneously disengages the driving means. In practice this deactuation means can comprise a piston-operated device to move the drive means away from the driven rollers. Thus, as soon as an item reaches the second sensor means the drive to that section of the conveyor is disengaged and the rollers can all rotate freely. The next item on the conveyor is driven from the preceding section onto the last section, where it will move freely over the rotatable rollers for a short distance, to activate the first sensor means.At this point the second sensor means on the preceding section becomes activated but the drive is still applied. It will then be seen that any subsequent item passing along the preceding section will reach the second sensor means in that section and cause the drive to be disengaged in that section. The pattern is then repeated down the length of the conveyor so that all the items become stopped at spaced intervals on the conveyor without bunching or collision and without being jostled over rollers which are still partially connected to drive means.

As soon as the first item is removed from the end of the conveyor the drive to that section is re-engaged and thus the second item is transported towards the end of the conveyor. As soon as that second item passes the first sensor means in the last section, the second sensor means in the preceding section becomes deactivated and the drive to that section (and hence to other preceding sections, becomes operative once more). Provided items are removed from the end of the conveyor, the drive in each section of the conveyor is maintained. As soon as an item is not removed from the end of the conveyor the drive is then arrested as before and assumulation begins.

Two embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic side elevation of two sections of a conveyor in accordance with one embodiment of the invention; Figure 2 is a sectional view showing two adjacent sections of a conveyor in accordance with a second embodiment of the invention; and Figure 3 is a partial transverse section of Fig. 2 showing some details of the drive.

The driven roller conveyor comprises a row of rollers 1 arranged in sections 2, 3. One of the rollers 1 in each section is arranged to be driven by a drive wheel 4, 4' which is in turn, powered by a drive belt 5 from a main power source, not shown.

The drive wheel 4 is arranged to be brought in and out of contact with a roller 1 by means of a piston 6, 6'. Near the end of the last section 2, there is situated a pressure sensing means 7 arranged to control the piston 6 so that when an article 8 on the conveyor passes onto the pressure sensor 7, the piston 6 withdraws the drive wheel 4 from contact with the roller 1. At the beginning of the section 2 another pressure sensor 9 is situated in such a position that a second article 10 on the conveyor will reach to sensor 9 once drive to the section has been withdrawn, while being driven from its previous section.

Obviously, the positioning of the sensor 9 will depend on the required spacing of the articles 8, 1 9 and on the distance for which an article 10 will roll under its own momentum. In practical cases this distance is very low to keep control of the process. If necessary, positive stops may be provided. The sensor 9 is arranged to activate another pressure sensor 11 at the end of the preceding section 3.

When so activated, a further article passing over the sensor 11 will cause the latter to actuate the disemgagement of the drive wheel 4' by actuation of the piston 6'. Preceding sections of the conveyor are constructed similarly.

When the article 8 is removed from the end section 2, the pressure sensor 7 deactuates the piston 6, thus re-engaging the drive wheel 4. The rollers in the section are then driven by the drive wheel 4 and slave drive wheels 1 2.

Article 10 thus moves along the section, freeing the pressure sensor 9. As soon as this happens, pressure sensor 1 is deactiviated and drive to the preceding section 3 is no longer interrupted by articles passing over the sensor 11. Provided articles are removed from the conveyor before they reach the sensor 7, the drive is maintained throughout the conveyor. However, if an article comes into contact with the sensor 7, the drive is progressively withdrawn from all the preceding sections of the conveyor so that the articles are stopped at pre-set spaced intervals.

It is important to note that actuation of the piston 6 disengages both the drive wheel 4 and the slave wheels 12, so that the drive to all the rollers 1 is interrupted. This prevents the rollers 1 being resistant to rotation and hence causing damage to the articles 8.

In the above described embodiment, each section 2, 3 is typically about 1 20 cm long and sections may be arranged in pairs up to a length of 15-20 metres.

Turning now to the embodiment of Figs. 2 and 3, the broad outlines of the operation are similar. However, the drive mechanism is somewhat indifferent, and the sensors are of a type to operate without contacting the articles being conveyed, thereby eliminating a possible cause of damage. The sensors may be proximity switches, or may operate by inter rupting a ray or by other suitable means.

As shown in above figures, the conveyor is made up of a series of driven rollers 1, and again two sections 2 and 3 of such rollers are shown, aithough a conveyor will normally consist of a considerable number of such sections. The sensors are shown at 21 and although operating differently from the microswitches shown in Fig. 1 they control rams 6 and 6' in the same way. The rams 6 and 6' each act to rock a frame section 22 and 22' respectively about a pivot axis 23. The frame sections 22 ar 22' carry pulleys 24 which support a drive belt 25 which is constantly driven by a pulley 26, itself being driven from a counter shaft 27. When the rams 6 and 6' are in the extended position, as illustrated from ram 6', the belt 25 is in engagement with the rollers 1 of its section and drives them. If the ram is retracted to the position shown for the ram 6, the belt is disengaged from the rollers, which thus becomes free to rotate but not to impart drive to the articles.

Various modifications may be made within the scope of the invention.

Claims (8)

1. A driven roller conveyor for transporting items characterised in that it comprises a plurality of separately driven sections, each section being individually provided with: driving means for driving rollers so that an item is transported along the section; Means for bodily shifting the driving means whereby the driving means can be engaged and disengaged with and from the rollers so that the rollers are selectively driven and free to rotate; and a first sensor means at the upstream end and a second sensor means at the downstream end of each section, said second sensor means being arranged to activate the deactuation means to disengage the drive means for that section on sensing an item, said first sensor means arranged to activate the second sensor means on the preceding section when said first sensor means senses an item, whereby the drive to the preceding section is disengaged by the next succeeding item to be sensed by said preceding second sensor means.

2. A driven roller conveyor as claimed in claim 1, in which the length of each section corresponds to the overall space occupied by two individual items.

3. A conveyor as claimed in claim 2, in which said driving means comprises a beltdriven driving wheel arranged to contact a roller, which roller in turn contacts a "slave" drive wheel is in contact with the next successive roller.

4. A driven roller conveyor as claimed in claim 1, in which the driving means comprises a drive belt tensioned so as to run over pulleys mounted to a pivoted frame actuated by a ram to move between positions in which the belt is engaged into and disengaged from the rollers.

5. A driven roller conveyor as claimed in claim 4, in which a single belt runs over pulleys and in two pivoted frame sections, each associated with a separate section of the conveyor to drive or release the rollers thereof.

6. A conveyor as claimed in any of the preceding claims, in which the sensor means are pressure-sensitive microswitches.

7. A driven roller conveyor as claimed in any of claims 1 to 5, in which the sensor means operate without contact with the items being conveyed.

8. A driven roller conveyor substantially as hereinbefore described with reference to Fig.

1 or Figs. 2 and 3 of the accompanying drawings.