GB2138140A

GB2138140A - Measuring lengths of workpieces

Info

Publication number: GB2138140A
Application number: GB08408534A
Authority: GB
Inventors: Bengt Axel Andersson
Original assignee: Waco Jonsereds AB
Current assignee: Waco Jonsereds AB
Priority date: 1983-04-07
Filing date: 1984-04-03
Publication date: 1984-10-17
Also published as: GB2138140B; GB8408534D0; SE8301902D0; DE3410614A1; SE8301902L; SE435870B

Abstract

For measuring the length of a workpiece (13), in particular a board in a cross-cut saw, at least the feed roller (14) disposed immediately before the cutting point has a measuring ring (16) rolling along the workpiece and radially movably accommodated in a groove in the feed roller (14), the rotational movement of the ring being transmitted to a measuring wheel (21). The measuring wheel engages the circumference of the measuring ring and exerts a downwardly directed force. When the feed roller (14) engages a workpiece (13), the measuring ring (16) is maintained in the groove of the feed roller such that, if the workpiece is planar, the peripheral surface of the measuring ring will be on a level with the peripheral surface of the feed roller (14) at the point where the feed roller (14) engages the workpiece (13), but will be moved out of the groove in case of depressions in the workpiece or when the rear end of the workpiece has passed the feed roller (14), in which case the measuring wheel 21 can be pressed against and driven by the feed roller (14). <IMAGE>

Description

SPECIFICATION Device for measuring the length of a workpiece The present invention relates to a device for measuring the length of a workpiece in a machine tool, in particular boards in a cross-cut saw which are fed along the machine table upto and away from the cutting point by means of feed rollers disposed adjacent and on either side ofthe cutting point and engaging the upperface of the workpiece.

In many cases, it is desirable to measure the length of a workpiece as it is being worked in a machine to allow the machine, on the basis of the measurement, to carry out working operations at predetermined points. One example of such a machine is a cross-cut saw in which boards are advanced by means of feed rollers along a machine table up to a saw blade for cutting. Before then, the points at which the cutting should be effected, for instance on either side of a knot-hole, have been determined and the positions of the cutting points have been stored in the memory of a microcomputor. As the boards enterthe cross-cut saw, the saw blade will be activated when said positions are opposite the saw blade. It goes without saying that an accurate length measurement ofthe board, which sets outfrom the end of the board, is of decisive importance.The measurement is normally carried out by means of a wheel which rolls along the board. Such an arrangement functions well but problems will arise if the boardsarevarying in length.

For measuring short boards the measuring wheel must in fact be located as closetothe saw blade as possible but since this space is occupied by the feed rollers, which must also be located as close to the saw blade as possible, the measuring wheel must be mounted ata location beforethefeed roller on the entry side ofthe machine, which means that the boards must have a certain minimum length to allow cutting with the required accuracy. Naturally, this is a substantial drawbackwhich results in an unnecessary waste of board material.

Although it might be possible to have the measuring wheel of the measuring instrument roll along the feed roller, this is a less reliable technique since the roller may slip on the workpiece which will of course give rise to measuring errors.

The object of the present invention therefore is to provide a measuring device which is capable, under the conditions stated above, ofalso measuring workpieces of short length.

According to the invention,this object is achieved in that a measuring ring rolling along theworkpiece is mounted on the feed rollerwhich is located before and/or afterthe cutting point, which ring is radially movable and freely rotatable relative to said feed roller and, when under radial load, can be so received in or moved our of a circumferential groove in the feed roller or a space associated with one end thereof, that the outer peripheral surface of the ring is maintained in engagement with the surface of the workpiece facing said peripheral surface, and in that a measuring Instrument with a measuring wheel is disposed above the feed roller with the measuring wheel vertically loaded againstthe circumference of the measuring ring to be driven by it.

By means of this device, the measuring ring will be maintained in engagementwith the surface of the workpiecefacing the ring, and the measuring wheel engaging the measuring ring will be driven with great accuracy. When the rear end of the workpiece has passed the feed roller, the measuring ring will be moved out of its groove and the measuring wheel is instead pressed against the circumference of the feed roller which will now drive the measuring wheel of the measuring instrument. The displacement ofthe work piece is effected by means ofthe feed roller which is located on the other side ofthe cutting point and whose movement of rotation is synchronised with that of the first roller.As mentioned above, there will then be a risk of incorrect measurement since the roller may slip on theworkpiece. However, the remaining distance oftravel is so shortthatthis risk can be disregarded. In case extremely great accuracy is required, the two rollers may each be provided with a measuring ring and a measuring instrument, and a sensor, for instance a photocell, may be adapted to sense the rear end oftheworkpiece as it passes the feed roller upstream ofthe cutting point and to switch to measurement by means ofthe measuring ring on the feed roller downstream of the cutting point.

The invention will be described in greater detail hereinbelowwith reference to the accompanying drawings which show an embodiment ofthe invention. Fig. 1 highly schematically shows an embodi ment ofthe invention from in front and Fig. 2 shows the invention in a simlarview and on a larger scale but with a different condition for measuring. The purpose of Figs. 1 and 2 isto illustrate the principle ofthe invention whereas Figs. 3 and 4 show a practical arrangementformounting a measuring ring. Fig. 3 illustrates the feed rollerwith the bearing means of the measuring ring as seen from in front and Fig. 4 shows the same arrangement as seen from above and partly in section.

In Fig. 1,a machine table in a cross-cut saw (not shown in greater detail) is designed 10. The cross-cut saw has a saw blade 12 which is movable in a vertical plane for cutting a workpiece in the form of a board 13 which is located above the saw blade and is fed along the table 10 by means offeed rollers 14 and 1 5 freely projecting from a bearing housing 11 and feeding the board 13 in the direction indicated by an arrow by peripheral engagement with the upper face ofthe board 13. The feed roller 14 located before the saw blade has a circumferential groove 33, as is intimated by dashed lines,aboutwhich a measuring ring 16is placed. The measuring ring 16 is axially non-displaceable butfreelyrotatable relative to the feed roller 14 and, as seen from the drawings, has a larger diameter than the feed roller 14. The diameter of the measuring ring 16 is shown on an exaggerated scale forthe sake of greater clarity but, in actual practice, it has a diameter which by but a few millimetres exceeds that of the feed roller 14. As will be understood from the following discussion, the measuring ring 16may also have a diameterequal to orsmallerthan that ofthe feed roller.The measuring ring 16, for instance as shown in fig. 4, is radially displaceably mounted in the groove in a suitable manner, and the ring 16 is of such dimensions that it can be inserted in the groove such that its peripheral surface will be on a level with the peripheral surface ofthe feed rolleratthe pointwhere the feed roller 14 engages the board 13, provided the board has a planar upperface. As appears from Fig. 1, the measuring ring 16willthereforethroughoutthe remainder of its circumference be substantially outside the circumference of the feed roller. Above the feed roller 14andthe measuring ring ? 16, a measuring instrument 17 is fixed on a lever 18 which is bent at right angles.The lever 18 carriesthe measuring instrument at the end of one arm while the end of its other arm is pivotally mounted on a pivot 20 fixed to the side wall of the housing 1 1,wherebythe lever arm supporting the measuring instrument 17 is vertically swingable, as shown buy a double arrow. The measuring instrument 17 has connected thereto a measuring wheel 21 whose circumference engages the circumference ofthe measuring ring 16. In orderto maintain the measuring wheel 21 in engagement with the measuring ring 16, there is provided a spring 22 between the lever 18 and an underlying fixing point on the housing 11.

The now described and schematically shown device operates in the following way. When a board 13 with a planar upperface moves along the table 10, the measuring ring 16will be urged into its groove atthe pointwherethefeed roller 14engagesthe board 13.

The measuring ring 16 rolls along the underlying board 13 and the rotation is transmitted to the measuring wheel 21 of the measuring instrument 17 to be supplied to the microcomputor. This goes on until the end ofthe board 13 passes the point of engagement between the feed roller 14 and the board 13. Since the prerequisite for pressing the measuring ring 16 into the groove in the feed roller 14 is now abolished, the ring 16 will be successively urged out of the groove at said point of engagement and instead pressed into the groove at the diametrically opposite side of the feed roller 14, as illustrated in Fig. 2.This means that the measuring wheel 21 is urged downwardly into engagement with the circumference ofthe feed roller 14soasto be driven by it asthe board 13 is being fed byte feed roller 15whose movement of rotation is synchronised with that of the roller 14. This means that the length ofthe board can be measured with great accuracy, whereby the waste of board material is reduced to a minimum, and that very short boards can also be cut.

To obtain very high accuracy,thetwofeed rollers 14,15 may each be provided with a measuring ring and the pertaining measuring instrument. In such a case, it is possible to provide a suitable sensor, for instance a photocell which senses the passage of the rearend ofthe board slightly before it leaves the engagement with the feed roller 14 before the cutting point, and switches to a measurement by means of the measuring ring ofthe feed roller 15. This of course presupposes that the measurements carried out by the two measuring instruments are synchronised.

Anyone of ordinary skill in the art realises thatthe vertically displaceable or pivotal mounting of the measuring instrument 17 with the measuring wheel 21 with force exertion againstthe measuring ring 16 is easy to accomplish, for instance as shown in the drawings, whereas the mounting ofthe measuring ring 16 in the groove 33 is somewhat more complicated, for which reason a practical embodiment thereof is shown in Figs.3 and 4.

Thefeed roller 14 in Fig. 4 consists of a jacket 35 which is non-rotatably mounted on a drive shaft 34 freely projecting from the bearing housing 11 in which it is mounted and driven in a suitableway (notshown in more detail). Asappearsfrom the drawing,the jacket35 ends at some distance from the bearing housing 11 and in the clearance space there is provided a circular plate 26 secured to a flange on the shaft 34 adjacentthe housing 11. The end surface of the jacket 35 facing the housing and the plate 26 define between them the above-mentioned groove 33. The groove 33 may of course also be disposed elsewhere in the feed roller butthe location shown in the drawing is the most advantageous.Closest to the drive shaft 34, the groove 33 is defined by a ring or sleeve 25 of a suitable plastic material mounted on the shaft. The measuring ring 16 is mounted in the groove 33. The ring 16 consists of a circular U-profile 23 whose web extends parallel to the end surface of the jacket 35 facing the housing 11. A coating 24 of a suitable material, such as rubber, is applied around the ring to the outer side of its outerflange. The profile 23 is supported by a plate 27 of a shape which appears from Fig. 3. A ring 28 is fixed by screws 29 to one flat side of the plate 27. The measuring ring 16 is mounted on the plate 27 by means of a bearing 30 whose outer bearing surface is connected to the inner circumference ofthe ring 28 while the inner surface of the bearing 30 is connected to the inner side ofthe innerflange ofthe measuring ring 16.The ring 16, like the bearing plate 27, has a central opening, the diameters ofthese openings exceeding the outer diameter ofthe sleeve 25 fixed on the drive shaft 34, which means that the measuring ring 16 and the bearing plate 27 are radially movable on the shaft34. For supporting the bearing plate 27, it has a projecting lug 37, as shown in Fig. 3, which is connected by a bearing element 31 to a shaft 32 which is mounted on the housing 11 in bearings 33.

As shown, the shaft 32 extends parallel to the drive shaft 34.

It appears from Figs. 3 and 4thatthe measuring ring 16 is movable in the groove 33 in the way defined in connection with Figs. 1 and 2 because ofthe oscillat- ing suspension ofthe plate 27. It is understood thatthe radial movementofthe measuring ring 16 relative to the feed roller 14 is determined bythe size of the openings of the measuring ring 16 and the plate 27.

Claims

-CLAIMS

1. A device for measuring the length of aworkpiece in a machine tool, in particular boards in a cross-cutsawwhich arefed along the machinetable up to and away from the cutting point by means of feed rollers disposed adjacent and on either side of the cutting point and engaging theupperface ofthe workpiece, wherein a measuring ring rolling along the workpieceismountedonthefeed roller which is located before and/or afterthe cutting point, which ring is radially movable and freely rotatable relative to said feed roller and, when under radial load, can be so received in or moved out of a circumferantial groove in the feed roller or a space associated with one end thereof, that the outer peripheral surface of the ring is maintained in engagement with the surface ofthe workpiece facing said peripheral surface, and wherein a measuring instrument with a measuring wheel is disposed above the feed rollerwith the measuring wheelverticallyloaded againstthe circumference of the measuring ring to be driven by it.

2. Device as claimed in claim 1,whereintheaxial extent of the measuring wheel is such thatthe measuringwheel is urged against the circumference of the feed roller when the measuring ring is pressed down into itsgroove because ofthe appearance of a depression in the surface of the workpiece or because the rear end oftheworkpiece has passed the feed roller.

3. Device as claimed in claim 1 or2, in which both the feed roller before and the feed roller afterthe cutting pointareprovidedwith measuring rings and measuring instruments and the feed rollers are synchronised, wherein a sensor, for instance a photocell, is provided for sensing the rear end of the workpieceasthisend passes the feed roller located before the cutting point, and theh switching to measurment by means of the measuring ring and measuring instrumentofthefeed roller located after the cutting point.

4. A device as claimed in claim 1 wherein the measuring instrument with the measuring wheel is mounted on a lever pivotally mounted on the machine frame and is maintained in engagementwith the circumference ofthe measuring ring by means of a tension spring mounted betweenthe leverandthe machine frame.

5. Deviceascaimed in claim 1 or2,inwhichthe feed roller has a drive shaft freely projecting from a bearing housing anda cylindrical jacketforengaging the workpiece, wherein the circumferential groove is provided between the end ofthejacketfacing the bearing housing and the bearing housing ora circular disc mounted on the drive shaft in front of the bearing housing, the measuring ring being rotatably mounted on a bearing plate which has a circular central opening with a diameter exceeding the diameter of the drive shaft, such that the bearing plate is radially movable in the vertical direction in a plane extending transversely ofthe drive shaft, and wherein the bearing plate has a substantially horizontally projecting lug which is fixed to a shaft rotatably mounted on the bearing housing and extending in parallel with the drive shaft ofthe feed roller.