GB2171225A

GB2171225A - A control system for pastry rolling

Info

Publication number: GB2171225A
Application number: GB08504379A
Authority: GB
Inventors: Stephen Dennis Hudd
Original assignee: PETER S SAVOURY PRODUCTS Ltd
Current assignee: PETER S SAVOURY PRODUCTS Ltd
Priority date: 1985-02-20
Filing date: 1985-02-20
Publication date: 1986-08-20
Also published as: GB8504379D0

Abstract

Pastry (P) is fed through a series of roller pairs (1a, 2a, 1b, 2b), progressively being squeezed thinner. To keep the loops between roller nips constant, the downstream rollers (1b, 2b) are driven faster than the upstream ones (1a, 2a). Each loop has a height sensor (3a) and deviations from a pre-set height (6a) are determined by a comparator (5a) and used to generate a relative speed change of the rollers between which that loop is suspended to keep the loop constant. The rollers are similarly governed to a pre-set speed, but this is over-ridden on demand from the loops. Thickness gauges (10a, 10b) just downstream of each roller pair have their outputs compared (11a, 11b) with a pre-set thickness (12a, 12b) and deviations from this are used to adjust the nip to keep the thickness constant. <IMAGE>

Description

SPECIFICATION A control system for pastry rolling This invention concerns a control system for pastry rolling. In a commercial bakery, pastry is not produced in small batches but in a continuous length which is passed through a succession of pairs of rollers that progressively squeeze the pastry from a thick 'sausage' down to a fairly thin sheet.

To some extent this is analogous to rolling out any malleable material, such as billets of red hot steel. The problem is that the thinner material emerging from a roller nip is travelling faster than the material entering that nip, and so when the material is unbroken between successive pairs, those pairs must be driven at different speeds, the downstream one faster than the upstream one. If the relationship is not exact, then the effect will either be that the rollers will try to stretch the material, or that they will ruck it up. With a material such as steel, this is not so likely to happen as merely some slight slippage by the rollers. However, pastry is of an entirely different consistency, strength, elasticity and temperature, and its co-efficient friction with the roller will also be different.It cannot stand much stretching without breaking, and if it does ruck up into folds, it could also break, or too big a thickness would try to squeeze into the nip of a roller pair.

The solution is not to support the pastry between rollers on some form of conveyor, but to let it loop down in a catenary. The spacing between adjacent roller pairs is enough to give latitude for variations in speed without immediate drastic alteration in the loop shape, but not so great that the pastry will break under its own weight.

According to one aspect of the present invention there is provided a control system for a succession of pastry rollers comprising means for sensing the height of a loop suspended between two roller pairs, means for comparing this height with a preset height and deriving an error signal, and means for using this error signal to alter the relative speeds of the two pairs in a sense to restore the loop to the preset height.

Where there are more than two pairs, each loop will have such a control system. Also, the error signal from one loop will be used to adjust the speeds of rollers not directly associated with that loop since, once one roller pair has its speed altered, those beyond it must be altered by the same amount to maintain the status quo of their loops.

The adjustment may be applied either to the upstream pair or the downstream pair.

Preferably, each roller pair will have means for sensing their speed, means for comparing this speed with a preset speed and deriving an error signal, and means for using this error signal to restore the roller speed towards the preset value, such restoration being subservient to any loop error signals demanding departure from the preset speed.

Thus, the rollers will be set to run at various speeds and will do so as long as the loops remain constant and correct. However, should those loops vary, the preset speeds will be overriden.

Conveniently, the loop height sensing means is a light roller which co-operates with the upper surface of the loop mid-way between the pairs of rollers, this sensing roller having a suspension whose condition gives an indication of the loop height.

According to a further aspect of the present invention there is provided a control system for a succession of pastry rollers comprising means for sensing the thickness of the pastry downstream of each pair of rollers, means for comparing this thickness with a preset thickness and deriving an error signal, and means for using this error signal to alter the nip between the associated rollers in a sense to restore the pastry towards the preset thickness.

Preferably, the thickness is sampled at intervals and a group of the most recent readings is averaged before comparison is made with the preset value. In this way, the odd small lump will not cause a sudden reaction.

As the nip is aitered, so the thickness of the pastry emerging from it changes, and this will also have an effect on the speed of delivery. The thinner the pastry, the faster it travels, and vice versa.

This alteration in speed will of course have an effect on the loop, and the loop sensing means will react. Thus, the two control systems will operate in conjunction to maintain correct speed and thickness throughout the succession of rollers.

For a better understanding of the invention one embodiment will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagram of a control system for a succession of pastry rolls, Figure 2 is a perspective view of a loop height sensor, and Figure 3 is a perspective view of a pastry thickness sensor.

In Figure 1, a web of pastry P is moved from right to left through two pairs of rollers 1a, 2a and 1b, 2b. Devices associated with the upstream pair of rollers will be referenced with the suffix a while corresponding devices associated with the downstream pair will have the suffix b. It will be understood that these roller pairs may be only part of a larger array progressively reducing the pastry thickness.

Midway between the pairs of rollers there is a loop height sensor 3a, shown in more detail in Figure 2. This has a roller 4a which bears lightly on the upper side of the pastry, and as the loop flattens or deepens the vertical movement of the roller is translated into a signal which is conveyed to a comparator 5a, whose other input is from a keyboard or corresponding device 6a by which a preset loop height signal is produced. Should the actual loop height vary from this the comparator produces an error signal which is fed to a unit 7a.

The roller la has a tacho device 8a associated with it which produces an actual speed signal, and this is also fed to the unit 7a, together with a pre set speed signal determined by keys 9a. The unit 7a compares the actual and preset speeds, and, in the absence of any loop error signal, produces a speed change signal which is fed to the drive (not shown) to the rollers la and 2a to restore them towards the preset speed. However, should there be a loop error signal, this will take precedence, and the roller speed will be adjusted to reduce that error.

A speed change signal may also be fed back from the corresponding unit 7b and added to the signal from unit 7a. For example, if the rollers 1b and 2b speed up, the rollers 1a and 2a must also increase their speed by the same amount to keep the loop constant. Similarly, these demands for speed change will be fed back upstream to affect all the other rollers as indicated by an arrow A.

Immediately downstream of the roller pair 1a, 2a, there is a thickness gauge 10a, shown in more detail in Figure 3. This has light roller contact with the upper surface of the pastry and is so near the rollers that changes in the shape of the catenary are insignificant as compared with changes in thickness resulting from alterations in roller spacing. This is translated into an electrical signal indicating actual thickness, and in a comparator 11a this value is compared with a preset one from a keyboard 12a. The resulting error signal is applied to a servo device 13a which will adjust the nip between the rollers in a manner to reduce the error signal.

In Figure 2, the loop sensor 3 is a transducer operating on the linear voltage displacement principle. The movement of the centrally divided roller 4 is transmitted via a rod 14 to a cylinder 15 which contains linearly wound primary and secondary coils. A ferrite slug on the rod 14 alters the magnetic coupling between the coils as the roller 4 moves up and down, and the voltage at the secondary output is thus indicative of the loop shape.

The sensor 3 is mounted on an adjustable bracket 16 fixed to a bar 17 spanning the loop. The roller 4 is stabilised and guided by struts 18 to its ends.

The thickness gauge 10 of Figure 3 operates on a similar principle, although here there are two discrete rollers 18 suspended from transducer units 19 carried by transverse bars 20.

Claims

1. A control system for a succession of pastry rollers comprising means for sensing the height ofa loop suspended between two rotating roller pairs, means for comparing this height with a preset height and deriving an error signal, and means for using this error signal to alter the relative speeds of the two pairs in a sense to restore the loop to the preset height

2. A control system as claimed in Claim 1, wherein there are more than two pairs of rollers, aligned to form a succession of loops, and wherein each loop is provided with such a control system.

3. A control system as claimed in Claim 2, wherein the error signal from one loop is used also to adjust the speed of rollers not directly associated with that loop in a sense to retain other loops constant.

4. A control system as claimed in Claim 1, 2 or 3, wherein each roller pair has means for sensing the roller speed, means for comparing this speed with a preset speed and deriving an error signal, and means for using this error signal to restore the roller speed towards the preset value.

5. A control system as claimed in Claim 4, wherein such speed restoration is subservient to any loop error signais demanding departure from the preset speed.

6. A control system as claimed in any preceding claim, wherein the loop height sensing means has a roller for co-operating with the upper surface of the loop mid-way between the pairs of rollers, this sensing roller having a suspension whose condition gives an indication of the loop height.

7. A control system for a succession of pastry rollers comprising means for sensing the thickness of the pastry downstream of each pair of rollers, means for comparing this thickness with a preset thickness and deriving an error signal, and means for using this error signal to alter the nip between the associated rollers in a sense to restore the pastry towards the preset thickness.

8. A control system as claimed in Claim 7 wherein the thickness is sampled at intervals and a group of the most recent samplings is averaged before comparison is made with the preset value.

9. A control system as claimed in Claim 7 or 8, in conjunction with a control system as claimed in any one of Claims 1 to 6.

10. A control system for a succession of pastry rollers substantially as hereinbefore described with reference to the accompanying drawings.