GB2401031A

GB2401031A - Improved cutting machinery

Info

Publication number: GB2401031A
Application number: GB0309667A
Authority: GB
Inventors: Adrian Richard Marshall
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-04-29
Filing date: 2003-04-29
Publication date: 2004-11-03

Abstract

Food products 9 such as cheese are cut using a tensioned wire 1 moved laterally and reciprocally along its length. A combination of motors 4, 5 and sprung or pneumatic components may control the lateral speed and tension of a cutting wire. The use of lateral motion reduces the force required to cut products, so there is less product damage and finer cutting wires can be used.

Description

Improvement to cutting machinery' Cutting with a tensioned wire is

commonly used method of cutting cheese industrially.

Tensioned wires are used in preference to knives, because when cutting large blocks with a knife, the cut surfaces of the cheese clamp the sides of the knife to give large friction forces that prevent further cutting motion (fig 1) This problem is in common with for other hard materials such as wood, and in the case of wood if you want to divide a block a saw is commonly used which has teeth to remove material in the form of chips or sawdust, and so allow the saw to penetrate further into the material. (fig 2) However for many food products the resultant ragged surface and wastage of the removed material due to sawing is not acceptable, and so ways or minimising any blade clamping friction are used.

The use of a tensioned wire is one common method, where, rather than using the thickness of a blade to support a cutting edge, tension is put across a length of wire to achieve a similar effect, but with the major difference being the considerable reduction in friction due to the smaller surface area of the wire compared with that of a knife. (fig 3) The disadvantage of a wire however is that the cutting edge cannot be 'sharp' like a knife, it is practically limited to the diameter of a wire strong enough to withstand the tension needed for the cutting action.

The relatively large size of cheese wires limits their widespread use on materials other than cheese If finer wires could be used, then the cutting forces for the finer cut would drop, so an even finer wire could be used, and so on (eventually limited by wire material properties) This invention concerns a way of reducing the forces on the wire to gain entry to this virtuous circle, for the benefit of the cheese preparation market initially but with the possibility of expanding the use of cutting wires across the food and wider process industries.

The concept is to feed the wme along its length whilst also pulling it through the cheese in the normal way. This can be preferably achieved by using a wme held between two servomotors running under appropriate control strategies: One motor will pull the wire though the product at a fixed (or profiled) speed, whilst the other motor will resist this lateral motion by imposing a fixed (or profiled) opposing torque.

Torque control (or more strictly motor current control) is commonly available on high

specification servo drives.

In this way one motor controls the wire motion the other the wme tension.

Once cil the wme on the drum has been used, the motors two swap roles and the cutting restarts with the wire moving in the opposite lateral direction.

Other methods of controlling tension such as sprung or pneumatic idlers may also be appropriate.

jays I Figure 4 shows a preferred embodiment A length of wire 1 is held on two drums 2&3 mounted on their respective motors 4&5. The amount of wire should be sufficient to minimise the number of reversals in wire travel resumed during the cutting of a typical product.

The wire leaves the drum and passes through vertical blade alignment slots 6 and 7, which compensate for the varying position of the wound wire across the drum. Vertical rollers or low friction or complementary materials may be used The wire passes over a cutting platen 8 on which the product to be cut 9 rests.

Preferably the relative position of the wire drums and cutting platen should be arranged so that the profile of the wire up to the product remains fairly consistent during the cut. This can be preferably done by raising the platen well above the drums, or by raising the height of the platen during the cutting process.

The platen may be profiled or have raised portions to resist the lateral motion of the wire.

Geometrical calculations can be made based on the known motion of each of the drums, to infer the approximate geometry that the wire is following, and then, having estimated the wire angle as it enters the product, the downwards force and tensile forces can be inferred, and controlled by adjustment of motor speeds and torques.

A set of weighing scales under the platen can be used to measure the downwards-cutting force experienced for troubleshooting, but this is not essential to the operation.

The two servos should have controllers capable of running in either torque control mode (whilst also reporting position) or in positional mode, (whilst also reporting torque). These controllers must be capable of switching between these modes on the fly.

The motors should preferably have the wire storage drums mounted directly onto their shafts (i.e. no gearbox or other gearing used) in order that losses in gearboxes are not encountered, and hence motor current most accurately indicates wire tension, Preferably a computer may be used for machine commissioning, to capture and process the fed back information (Motor position, torques and scale readings to provide diagnostic information), and it may be a suitable way to control the motor mode and sequencing.

Final embodiments may have dedicated controllers An example of operational strategy follows to illustrate a preferable method of operation (fig 5) Placing product and homing To wind to start of wire rotate first motor and drum 11 and second motor and drum 12 anticlockwise in position mode until torque feedback from motor and drum 12 indicates end of wire To throw up a loop of wire rotate first motor and drum 11 clockwise to release an appropriate length of wire.

Insert the product to be cut under the wire To wind back the slack, rotate first motor and drum 11 anticlockwise until torque feedback from motor and drum 12 indicates the wire is taught.

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Cutting product (forward pass) Run the first motor and drum 11 in torque mode, controlling torque to required value whilst rotating second motor and drum 12 clockwise in position control mode until interpretation of the positional information from the first motor and drum 11 indicates that it has 'dispensed' all its wire, or alternatively positional information from both motor and drums 11 and 12 indicate that the product must be cut through, in which case stop both motors and remove the cut product.

Cutting product (return pass) Run the second motor and drum 12 in torque mode, controlling torque to required value whilst rotating first motor and drum 11 anti clockwise in position control mode until interpretation of the positional information from the second motor and drum 12 indicates that it has 'dispensed' all its wire, or alternatively positional information from both motor and drums 11 and 12 indicate that the product must be cut through, in which case stop both motors and remove the cut product.

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Claims

Claims 1. A tensioned wire cutting device which includes lateral motion of

the wire along its length to improve cutting effectiveness.
2. A device as claim 1 which uses multiple motors to control the lateral speed and tension of a cutting wire.
3. A device as claim 1 which uses a combination of motors and sprung components to control the lateral speed and tension of a cutting wire.
4. A device as claim 1 which uses a combination of motors and pneumatic components to control the lateral speed and tension of a cutting wire.

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