WO1997000761A1

WO1997000761A1 - Mitre cutter

Info

Publication number: WO1997000761A1
Application number: PCT/GB1996/001501
Authority: WO
Inventors: Richard Walker
Original assignee: The Moulding Group Ltd.
Priority date: 1995-06-22
Filing date: 1996-06-21
Publication date: 1997-01-09
Also published as: GB9512750D0

Abstract

A computer controlled automatic mitre cutter for picture frame and similar mouldings comprises a bed (14) on which a length of moulding (17) is fed by a feed gripper (15) having a continuously variable drive provided by a rotary lead screw (21), to a cutting head (11). The head is reciprocated to cut a mitre in a series of cross-cuts, between which it is laterally driven by another continuously variable drive provided by a further rotary lead screw (23). Sensors (19, 20) sense the position of the feed gripper (15) and of the the cutting head (11), and rotary encoders (22, 25) produce series of pulses in response to the movement of the rotary lead screws (21, 23) respectively. The computer (18) is programmed to provide control signals to the gripper drive (21) and cutting head (11) in response to operator-input data concerning the moulding (17) and the pre-selected lengths to be cut and the signals from the sensors (19, 20) and encoders (22, 25).

Description

MITRE CUTTER

This invention relates to an apparatus and to a method for cutting mitres in lengths of material. It was particularly devised for cutting picture frame mouldings for making up into picture frames, but may be used for cutting mitres in other materials. For convenience of description, however, all such lengths of material will be referred to as "mouldings".

In traditional hand processes for making frames, a mitre is cut using a saw, often with a mitre box to guide the cut. Such methods are inaccurate and time consuming and do not lend themselves to automated or large-scale production.

Conventional production-line methods have involved the use of a N-shaped guillotine blade which is reciprocated generally perpendicular to the length of the moulding. This gives a precise control of the angle of the mitre cuts, but it may be difficult to prevent damage to the face of the moulding. A great variety of different mouldings are available in different materials such as hard and soft woods, plastics and composite materials, and with finishes such as varnish, paint, foils, or papers. The action of shearing through the material from the decorated surface can cause visible damage such as chipping, distortion or tearing of the surface finish.

Current guillotine apparatus also require constant operator attention to feed and align the lengths of moulding and to operate the blade.

It has been proposed to provide a power operated mitre cutting apparatus in which a moulding is fed stepwise to a reciprocable guillotine blade.

It is an object of the present invention to provide a mitre cutting apparatus having an automated computer controlled operating system. Viewed from a first aspect, the invention provides a computer controlled apparatus for cutting mitres in an elongate moulding and viewed from a further aspect the invention provides a computer when programmed to control such an apparatus.

According to a first aspect the invention provides an apparatus for cutting mitres comprising:

a machine bed adapted to receive a length of moulding;

a reciprocable cutting head adapted to cut a mitre in said moulding and;

a feed gripper adapted to grip the moulding, the feed gripper being movable along the bed to feed the moulding to the cutting head;

computer means having input means for data on the moulding and on pre-selected lengths to be cut;

a continuously variable gripper drive;

a gripper drive sensor adapted to sense the position of the gripper relative to a datum position and to generate a signal in response to sensing said position;

the computer being adapted to receive said signal and to provide control signals to operate the continuously variable gripper drive and the reciprocable cutting head in response to a predetermined algorithm to cut the pre-selected lengths from the moulding.

The reciprocable cutting head may also have a continuously variable lateral drive and a further head drive sensor may be provided to sense the position of the head relative to a datum position and to generate a signal in response to sensing said position; the computer being adapted to receive said cutting head position signal and to provide control signals to operate the continuously variable lateral drive to the cutting head.

Preferably, the continuously variable gripper drive and/or the continuously variable lateral drive to the cutting head are provided by rotary lead screws.

The gripper drive sensor and head drive sensor may comprise rotary encoders adapted to produce a series of pulses in response to rotation of the lead screw.

According to a further aspect the invention provides a computer programmed to operate a mitre cutting apparatus as set out above.

Figure 1 diagrammatically illustrates a length of moulding and the way in which it may be divided up by the apparatus,

Figure 2 is a plan view, with interior parts revealed, of the left hand end of a mitre cutter embodying the invention showing feed means,

Figure 3 is a plan view with interior parts revealed of the right hand end of the mitre cutter showing a cutting head,

Figure 4 is a front elevational view diagrammatically illustrating a mitre cutter embodying the invention.

Referring to the drawings, a mitre cutting apparatus generally indicated at 10 comprises a reciprocating V-shaped cutting head 11 which has a guillotine cutting action against a fixed V-shaped throat 12 in generally known manner. The head is reciprocated up and down by head drive means generally indicated at 13 which do not form part of this invention and will not be described in detail. An electric motor having a brake operating in a "fail safe" mode drives a rotary shaft through a gearbox and a crank is used to convert the rotary movement to vertical reciprocating movement of the cutting head. The apparatus 10 includes a bed 14 which is elongate and for the purposes of the following description can be considered to stretch from a feed end at the left to a cutting position at the cutting head 11 on the right. Lengths of moulding to be mitred are placed on the bed either manually or by mechanical means and the operation of the cutting apparatus in principle involves the moulding being gripped by a gripper 15, fed stepwise towards the right to the cutting head 11 where rebate clamps 16 grip the rebate of the moulding to hold it steady, and top clamps 16a clamp the moulding 17 to the bed 14. This clamping is followed by vertical reciprocation ofthe cutting head 11 to cut a V-shape in the moulding. The cutting head 11 is incrementally moved laterally across the moulding 17 and is then reciprocated again so as to make a deeper V-shaped cross-cut. This cross-cutting procedure may be repeated a number of times, under the control of the computer which in turn is instructed by the operator. When the final cut has been made, this severs the moulding leaving a cut-off length to the right of the cutting head 11 which is removed from the cutting zone by suitable transfer means, forming no part of this invention. To the left of the cutting head, there remains the main length of moulding which is again incrementally fed by the gripper 15 to cut off the next length of moulding.

The apparatus is controlled by a computer 18 and has feed means for the gripper 15 and cutting head 11 which are particularly adapted for computer control so as to give flexibility of operation, and precision of cutting. In particular, the computer can be programmed to provide variation in the cut lengths of moulding passing through the machine to provide for example alternate long and short lengths of moulding in the appropriate sequence for making up rectangular frames. The apparatus can also sense the length of the moulding which it is cutting and is programmed so as to minimise waste.

Initial Set-up

Referring to Figure 1, the computer 18 requires the input of various dimensions of the moulding including the raw length AB ofthe moulding, the width W ofthe moulding and the "qualifying cut" CB required. This is a typical length to be cut off the front end of the moulding in order to remove any ragged or damaged portion and to provide a mitred cut at the leading end of the first piece to be cut.

It is also required to input the inside width DE and inside height FG of the frame to be made because these are the dimensions which determine the lengths of the moulding to be cut. The computer can then calculate, using the width W of the moulding already input, the centre lines K, L, M .... ofthe mitre cuts. A small amount ofthe length of the moulding will be removed at each mitre cut and the amount of this will typically be 1.5mm, the figure which will be held in the general set-up instructions of the computer as distinct from being programmed in for each batch of mouldings.

Additionally, the operator will programme the number of incremental stages or cross-cuts in which the mitre cut is made in the moulding. This will depend on the skill and experience of the operator or may be determined experimentally for any particular type of moulding. The apparatus will cut wood, cellular or non-cellular plastics material, or wood based particle material such as MDF. Each of these difference materials may require a different number of incremental cross cuts to be made.

The computer can calculate the amount of the moulding left over after each length is cut because it knows the raw length of the moulding, the qualifying cut, the amount of loss at each mitre cut and the number of lengths which have so far been cut from the moulding. By a subtraction routine, the computer can determine when no further pairs of the required lengths can be cut from the remaining length AH of moulding. At this point, a secondary cutting routine is commenced to make one or more shorter lengths as instructed by the operator. These desired shorter lengths PQ, RS are also input at the set¬ up stage. Once the shorter lengths can no longer be cut from the raw length of moulding, the final portion AT is discarded as scrap. Suitable means are provided for removal of scrap and trimmings from the machine, for example using an air blast.

These stages are diagrammatically illustrated in Figure 1.

Sensing Devices The gripper 15 is provided with two photoelectric sensors namely a leading sensor 19 and a trailing sensor 20. These are directed laterally across the moulding and have the function of indicating to the computer 18 the presence or absence ofa length of moulding on the bed 14. Where one of the sensors indicates the presence of a moulding and the other sensor indicates its absence, it is clear that one ofthe ends ofthe moulding has been reached, either the leading end or the trailing end.

The gripper 15 is engaged laterally with the moulding and is caused to move along the bed 14 in the direction of arrow A, so as to feed the moulding longitudinally. The gripper is driven by a lead screw 21 which is rotated from an electric motor 9. An encoder 22 associated with the lead screw 21 indicates the number of revolutions and fractions of a revolution of the lead screw and therefore gives precise numerical signals indicating the position of the gripper along the length of its travel. These signals are fed to the computer and are incorporated in the calculations for cycling the apparatus 10.

The cutting head 11 is incrementally moved transversely across the moulding between cuts as described above and this cross-cut movement is also carried out by a lead screw 23 rotated by an electric motor 24. A further encoder 25 is used to detect the amount of movement of the head and a numerical signal is again passed to the computer 18 for use in calculations.

The use of lead screws and the detection afforded by the encoders 22 and 25 enables very precise positioning of the moulding (via the gripper) and the cutting head 11.

Further sensors may be provided for example to detect the presence of the moulding at the cutting head, any obstruction in the way of the cutting head, the engagement of the gripper 15 and of the clamps 16, 16a and the correct positioning of the machine guards 8 during operation.

Sequence of Operations The following listing gives the sequence of operations required to perform the functions mentioned above under the control of the computer 18. For convenience of description, it is divided into a loading and feeding sequence and a cross cut or mitre cutting sequence.

Loading and Feeding Sequence

1. Moulding 17 arrives on bed 14.

2. Sensors 19 and/or 20 detect moulding 17.

3. Search routine (right). Gripper 15 moves left and searches for lead end of strip determined by moulding being sensed present by trailing sensor 20 and absent by leading sensor 19.

4. Computer 18 instructs gripper 15 to move left to produce qualifying cut. Distance of movement calculated by comparing position of gripper 15 with datum, subtracting qualifying cut length CB.

5. Gripper 15 moved laterally at new position to grip moulding. Lateral movements stopped on reaching pre-set width W of moulding and/or on signal from gripper sensor.

7. Gripper moves right to position moulding for qualifying cut at mitre cutting head 11. Encoder 22 signals computer 18 when gripper has moved the required distance.

8. Rebate clamps 16 and top clamps 16a engage moulding at cutting head.

9. Gripper 15 disengages moulding and moves left to its maximum left position, substantially at the left hand end of the bed 14. The leading and trailing sensors 19 and 20 normally detect the continuing presence of the length of moulding 17 at this position but if photoelectric sensor 20 passes the end of the moulding, moulding end routine takes place (see below).

10. Once the gripper 15 has moved clear from the position of the cutting head, the cross cut sequence (set out in more detail below) takes place.

11. After cross cut sequence, rebate clamps 16 and top clamps 16a disengage.

12. Gripper 15 feeds right to feed the next length of moulding to the cutting head 1 1. The computer calculates the feed distance as equal to the length (DE or FG alternately) requested by the operator plus twice the width of the moulding plus 1.5mm, the default trimming distance and lead screw is rotated to feed the gripper right by the exact amount.

13. Rebate clamps 16 and top clamps 16a engage. Steps 9-12 are repeated.

14. Cross cut routine below takes place.

15. After clamps 16 and 16a engage, the computer determines whether the remaining portion of strip between gripper and cutting head is sufficient for the next length to be fed. If so, gripper remains in position.

16. If not, gripper 15 disengages and lead screw is reversed to move gripper to maximum left position and re-engaged.

17. Moulding end routine occurs when photoelectric sensor 20 indicates end of strip. Gripper positions at minimum grip position on strip.

18. Cycle continues cutting alternate long and short members from primary operator input until insufficient moulding length AH remains. 19. Computer then substitutes shorter pre-selected moulding lengths (PQ, RS) and cycle continues until no further selected lengths can be obtained from the remaining portion AT of moulding.

20. When rebate clamps and top clamps 16 and 16a are engaged on final cut, gripper returns fully to the left to pick up a new moulding length 17.

21. If no new moulding detected, apparatus goes to standby condition.

Cross Cut Sequence

A. Moulding 17 fed to cutting head 11 as described in feed sequence above.

B. Lead screw 23 rotated to move cutting head 11 to first position pre-set by operator input. Further encoder 25 signals computer 18 and lead screw 23 stopped accordingly.

C. Rebate clamps 16 advance to clamp rebate. Clamping determined either by width W input by operator or by sensors on rebate clamps.

D. Top clamps 16a advance to clamp top of moulding. Again clamping distance determined either by input from operator or by sensors.

E. Cutting head 11 reciprocates to make initial cut.

F. Rebate clamps 16 retract.

G. Lead screw 23 rotates and encoder signals position until cutting head 11 reaches next position.

H. Steps C-G are repeated until final cut is made. Head is retumed to datum by reverse rotation of lead screw 23. Further encoder 25 indicates when this is completed.

Claims

1. An apparatus (10) for cutting mitres comprising:

a machine bed (14) adapted to receive a length of moulding (17);

a reciprocable cutting head (11) adapted to cut a mitre in said moulding (17)and;

a feed gripper (15) adapted to grip the moulding (17), the feed gripper (15) being movable along the bed (14) to feed the moulding (17) to the cutting head (11);

characterised in that there are provided computer means (18) having input means for data on the moulding (17) and on pre-selected lengths to be cut;

a continuously variable gripper drive (21);

a gripper drive sensor (19, 20) adapted to sense the position of the gripper (15) relative to a datum position and to generate (22) a gripper position signal in response to sensing said position;

the computer (18) being adapted to receive said gripper position signal and to provide control signals to operate the continuously variable gripper drive (21) and the reciprocable cutting head (11) in response to a predetermined algorithm to cut the pre-selected lengths from the moulding (17).

2. Apparatus according to Claim 1 further characterised in that the reciprocable cutting head (11) has a continuously variable lateral drive (23) and a further cutting head drive sensor is provided to sense the position ofthe cutting head (11) relative to a datum position and to generate (25) a signal in response to sensing said cutting head position; the computer (18) being adapted to receive said cutting head position signal and to provide control signals to operate the continuously variable lateral drive (23) to the cutting head (11).

3. Apparatus according to Claim 1 further characterised in that the continuously variable gripper drive is provided by a rotary lead screw (21).

4. Apparatus according to Claim 3 further characterised in that the gripper drive sensor comprises a rotary encoder (22) adapted to produce a series of pulses in response to rotation of said gripper drive rotary lead screw (21).

5. Apparatus according to Claim 2 further characterised in that the continuously variable lateral drive to the cutting head is provided by a cutting head rotary lead screw (23).

6. Apparatus according to Claim 5 further characterised in that the head drive sensor comprises a further rotary encoder (25) adapted to produce a series of pulses in response to rotation of the cutting head rotary lead screw (23).

7. A computer (18) programmed to operate a mitre cutting apparatus (10), the apparatus (10) comprising a machine bed (14) adapted to receive a length of moulding (17). a reciprocable cutting head (11) adapted to cut a mitre in said moulding (17), and a feed gripper (15) adapted to grip the moulding (17), the feed gripper (15) being movable along the bed (14) to feed the moulding to the cutting head (11), a continuously variable gripper drive (21), a gripper drive sensor (19, 20) adapted to sense the position of the gripper (15) relative to a datum position and to generate (22) a gripper position signal in response to sensing said position; the computer (18) having data input means for data on the moulding (17) and on pre-selected lengths to be cut; the computer being programmed with a predetermined algorithm and being adapted to receive said gripper position signal (22) and to provide control signals to operate the continuously variable gripper drive (21) and the reciprocable cutting head (11) in response to said predetermined algorithm to cut the pre-selected lengths from the moulding (17).

8. A computer (18) according to Claim 7 programmed to operate a mitre cutting apparatus (10) wherein the reciprocable cutting head (11) has a continuously variable lateral drive (23) and a further cutting head drive sensor is provided to sense the position of the cutting head relative to a datum position and to generate (25) a signal in response to sensing said cutting head position; the computer (18) being programmed to receive said cutting head position signal and to provide control signals to operate the continuously variable lateral drive (23) to the cutting head (11).

9. A computer ( 18) according to Claim 7 further characterised in that the continuously variable gripper drive is provided by a rotary lead screw (21) having a rotary encoder (22) and the signal from said gripper drive sensor comprises a series of pulses generated by said rotary encoder (22) in response to rotation of said gripper drive rotary lead screw (21).

10. A computer (18) according to Claim 8 further characterised in that in the continuously variable lateral drive to the cutting head is provided by a rotary lead screw (23) having a further rotary encoder (25) and the signal from said head drive sensor comprises a series of pulses generated by said further rotary encoder (25) in response to rotation of said cutting head rotary lead screw (23).