US3908723A

US3908723A - Numerical controlled bandsaw for keyboards

Info

Publication number: US3908723A
Application number: US454443A
Authority: US
Inventors: Robert S Hill
Original assignee: Wurlitzer Co
Current assignee: GIBSON PIANO VENTURES Inc A DELAWARE Corp; TWCA CORP
Priority date: 1974-03-25
Filing date: 1974-03-25
Publication date: 1975-09-30
Anticipated expiration: 1992-09-30
Also published as: JPS50128890A; IT1029782B; GB1469038A; DE2512463A1; CA1011225A

Abstract

A wood blank for the production of a piano keyboard or the like is secured to a platform. A three axes numerical control is provided. Two of these axes effect movement of the base on which the blank is mounted to move the blank in X and Y directions. The third axis numerical control is used to twist the blade of the bandsaw simultaneously with movement of the blank or workpiece in the X and Y directions.

Description

1 1 Sept. 30, 1975 United States Patent Hill Crane et a1.

1 NUMERICAL CONTROLLED BANDSAW FOR KEYBOARDS Lindholm....

t" C em I t C t n l 1H c P. 34 77 0/9 24 60 6 102 0 33 [75] Inventor: Robert S. Hill, Holly Springs, Miss The Wurlitzer Company, Chicago.

[73] Assignee:

Primary E.\'aminerFrank T. Yost Atrorney, Agent, or Firm-Olson, Trexlen Wolters, Bushnell & Fosse, Ltd.

[22] Filed: Mar. 25, 1974 Appl. No.: 454,443

[57] ABSTRACT A wood blank for the production of a piano keyboard [52] US. 144/2 R: 83/71; 83/410;

or the like is secured to a platform. A three axes numerical control is provided. Two of these axes effect OJW 8 -00 a ww s .w s7 99 87 7 C 7 MC 5 y? 4 2 W4 0 N1 m S00 f References Cited UNlTED STATES PATENTS 2,774.131 Crane 83/789 X D 2.792.033 5/1957 83/747 7 Clam, 4 Drawmg Flgurefi U.S. Patent Sept. 30,1975 Sheet 1 of2 3,908,723

US. Patent Sept. 30,1975 Sheet20f2 3,908,723

L x Ax/s M0 TOR 3 AXES NUMERICAL j Y Axls MOTOR CONTROL 33 I SYSTEM 2 Ax/s MOTOR TAPE BUFFER MAI/V SYSTEM READER STORAGE 1.06/6

Q7 0051 ff CONTROL MAIN SYSTEM INFORMATION LOGIC such cutting was often effected by means of a bandsaw with manual feeding and control of the workpiece. This has required rather considerable skilled labor, and has become prohibitively expensive. In order to reduce the cost of such prior art manual operation, various mechanically or electrically controlled feed mechanisms have been developed, one such being disclosed in Andersen US; Pat. No. 3,158,185.

In accordance with .one present automatic keyboard sawing apparatus the keyboard blank or board. is fed in a straight line at the angle of the flair of the keyboard 'read from the buffer storage while the machine is makto the flair point of.-theboard, at which point the board I.

is rotated, and then fed straight again. The angle of the flair of the keys is determined by indexing stops. The board is shifted. along an index bar peripendicular to the sawblade to establishthe key width.

In accordance with one key design it is desirable to have a double flair to-each key so that the back or inner end of the keys will run straight under the whips in a direct blow key and action combination. Since the keys of some keyboards utilize this double flair construction,

while others do not,- it is desirable that an apparatus be I able to saw either type. In present keyboard sawing apparatus it is necessary for the table movement to stop as the board is rotated to a new position, and this limits the speed of operation.

The fact that each key in a conventional piano key- I "board is different from the one next to it precludes the use of tracer type mechanisms. Efforts to develop a mechanism that would move the board in two axes while turning the board so that the blade could always ..be in the plane of the cut have resulted in mechanisms 1 that have been extremely complex and difficult to operate.

OBJECTS AND BRIEF DESCRIPTION It is an object of the present invention to utilize athree axes numerical control of a bandsaw apparatus for sawing piano keyboards and the like.

A further object of the present invention is to provid ,apparatus for sawing piano keyboards at maximum speeds available with-current machinery.

In accordance with the present invention a three axes numerical control is used with the board or workpiece being moved in two axes, and with the third axis control effecting twist of the sawblade up to 450 to either side.

Sawing is-around curves rather than with an abrupt change in direction, thereby simultaneously improving the appearance of keyboards, reducing saw breakage by eliminating abrupt twisting of the sawblade, and speeding up the sawing operation since it is unnecessary to stop table movement to rotate the board to a new position. r

. Some of the. keys to becut have two short segments of are that connect. Forty to fifty bits or characters are required by the numerical control systems in order properly to program the circular interpolation system within the controls. The same total amount of information must be supplied to contouring control to produce the desired shape whether the radius being cut is large or small, and without regard to the length of the arc.

Even though tape readers used in the system run at 300 characters per second, they do not read information into the controls fast enough to allow the saw to make two of these short arcs, one immediately behind the other, at the speed in which it is desired to operate the equipment. This is not a problem at relatively low speeds, or with long straight cuts, or on long segments of are.

In accordance with the present invention a buffer storage is provided into which the tape can readinformation, which buffer storage will be large enough to store more than enough information to make several short segments of arc. Sufficient information then is ing fairly long straight cuts to allow the machine to con- -tour without having to wait for the tape. In accordance with a preferred example of the present invention the buffer storage or memory is a 132 character memory.

This is useful is sawing keyboards when two short curves requiring as many as characters are followed by at least two straight line moves that require 6 to 7 characters each.

As an alternative to this, control information is stored on a memory disc or in a mini-computer, whereupon the limitation imposed by tape reader speed no longe exists.

DESCRIPTION OF THE DRAWINGS The present invention will best be understood with reference to the drawings when taken in connection with the accompanying following text wherein:

FIG. 1 is an exploded perspective view, somewhat schematic in nature, showing a bandsaw constructed in accordance with the present invention;

FIG. 2 is a schematic diagram illustrating the principles of the invention; I

FIG. 3 is a schematic drawing illustrating thelogic asv pects of the invention utilizing a tape reader and a buffer storage; and

FIG. 4 is a diagram similar to FIG. 3 but eliminating the buffer storage. DETAILED DESCRIPTION OF THE DISCLOSURE Referring first to FIG. 1 there will be seen abase 10 which is secured in any suitable manner to a standard bandsaw. An X axis drive motor 12 is mounted on this base, and comprises a reversible motor. The motor 12 acts through a screw drive 14 to drive a block 16 toward and away from the motor 12 along the X axis.

The base 10 is provided with a plurality of ways 18,

' illustrated as 2 in number, parallel to the screw drive 18 and spaced above the base 10 by means of supports 20.

Bearing blocks 22 secured beneath the corners of a X axis table 24 receive the ways 18 and slide back and forth thereon, the block 16 secured to the underside of I the table 24. Thus, the position and speed of the table 24 at any time is determined by the block 16, and

hence by the X axis drive motor 12 and screw drive 14.

The X axis table is provided with a plurality of ways 26, again illustrated as 2 in number and supported above the X axis table by supports 28 along opposite sides thereof.

The X axis table is provided with a Y axis drive motor 30 secured to the table, and having a screw drive 32 extending in the Y axis direction. A block 34 having a nut therein receives the screw drive 32 for movement back and forth in the Y axis direction under the influence of the Y axis drive motor 30.

A Y axis table 36 is secured to block 34 and is provided on its underside, illustratively at the four corners thereof, with bearing blocks 38 receiving the Y axis ways 26 for movement of the Y axis table 36 in the Y axis direction along with the block 34. A mounting plate or fixture 40 secures the workpiece or board 42 on the Y axis table 36.

A bandsaw, shown only in part at 44, includes a blade 46 having teeth 48 along the front edge thereof. The bandsaw 44 includes a fixed table 50 which is fixed relative to the base 10. the sawblade 48 passes through a slot or notch 52 in the table 50, and also passes through vertically spaced guides 54 and 56 which are in fixed relation to the table 50, but rotatable relative thereto in order to twist the blade to either side of its normal position.

A block 58 or other suitable structure supports a Z axis drive motor 60 from and above the table 50. The Z axis motor has an output shaft 62 which, like the screw shafts l4 and 32 of the X and Y axis motors respetively is rotatable in either direction. The shaft 62 passes through a bearing wall 64 and is provided with a spiral gear 66 fixed thereon. This gear meshes with a spiral gear 68 on a shaft 70 which is at right-angles to the shaft 62 and parallel to the illustrated reach of the sawblade 46. The shaft 70 is supported in suitable bearings such as on or in the table 50 and spaced thereabove, and is provided on either side of the gear 68 with a pair of

pulleys

72 and 74, respectively on a level with

pulleys

76 and 78 fixed to the saw guides 54 and 56. Suitable belts or bands 80 and 82 connect the respective pairs of pulleys. Accordingly, rotation of the Z axis motor 60 acts through the

gears

66 and 68 and the sets of pulleys simultaneously to turn the

guides

54 and 56, whereby to twist the bandsaw blade 46 in either direction from its normal position.

Turning to the second sheet of drawings, and first to FIG. 2, there will be seen schematically illustrated a three axes numerical control system 84 having three

output lines

86, 88 and 90 respectively leading to the X axis motor 12, the Y axis motor 30, and the Z axis motor 60.

In accordance with a preferred embodiment of the invention, the three axes numerical control system includes a tape reader 92 (FIG. 3) having an output at 94 connected to a buffer storage 96. The buffer storage 96 has an output at 98 to a main logic system 100 having the

output lines

86, 88 and 90 previously referred to. The main logic system also has a control line 102 connected back to the buffer storage 96 to call for information from the buffer storage at the proper time.

As an alternative, see FIG. 4, there is a control information apparatus 104, which may be a memory disc or a mini-computer, having an output at 106 leading direct to the main logic system 100a, having the

outputs

86, 88 and 90.

The three axes numerical control system as just disclosed permits the completely automatic sawing of a piano keyboard or the like at a maximum rate. It is to be realized that the problems involved in cutting a slot with a sawblade are quite different from those when a slot or pattern is to be cut with a round tool, i.e., a router, the latter requiring only two axis control to produce the desired pattern.

Currently available bandsawing machines used in the production of piano keyboards have a maximum feed rate of about 400 inches per minute. Such machines have a sawblade travel speed in excess of 8,400 feet per minute. Calculations based on this with current tooth spacing show that if the keyboards were to be fed at 800 inches per minute, chip load per tooth on the sawblade would be approximately 0.001 per tooth. This is a very small amount. Sugar pine is the wood currently used for keyboards, and tests have been made to determine the pressure against the sawblade when cutting sugar pine at high speed. With the board pushed as rapidly as possible through the bandsaw a maximum pressure of 10 pounds was recorded. This is a relatively small force and one which the bandsaws are well capable of withstanding. The current apparatus has been designed within the foregoingcapabilities, and is quite capable of sawing keyboards with a rate of 800 inches per minute, double the existing commercial rates without changing currently available bandsaws except for the control thereof. Within the capabilities of currently available bandsaws, the blades can readily be twisted 45 to each side of center without damaging the blades. A sawblade Vs inch in length (in the direction of feed) can cut 1% inch radius.

All machine and control systems have a characteristic called gain" which is expressed in terms of inches of movement per minute per one thousandths lag. The gain of a system determines the acceleration and decelleration rates of the moving component, and also the amount by which the actual position of the work or tool will be behind, or following, the positioning signals being generated; for example, a control system with a gain of one inch per minute per thousandth will have a lag of l/1000 (.001) when moving at a speed of one inch per minute. There would bea lag of one inch when moving at a speed of one thousand inches per minute. The maximum gain that may be applied to any axis is dependent on the inertia reflected to the drive motor, and, of course, the characteristics of the drive motor itself. The recognized formula for determination of maximum gain is: Gain TpK 60 10* /2 PVI Where:

Gain is in IPM/0.00l inch Tpk available peak torque in inch-pounds P ball screw pitch V maximum desired velocity I total inertia In a system containing more than one axis operating in synchronism (note that there are three simultaneous axes in the invention as heretofore disclosed), all axes must be set to equal gains to insure accurate path control.

If one axis of the machine is traveling full speed and then a second and third axis are commanded to move,

the path of the tool or workpiece is distorted for two of the tool isaffected is the fact that there is a'time lag ent invention as it is necessary to cut into the board or" workpiece, and then to track back through the same slot with a rather high degree of accuracy so that the blade will clear as it backsout. Accordingly,.it is necessary to have a gain high enough to keep the following errors small, but not so high that the accelleration forces on the machine components would be destructive.

The driven components (tables and rotating mechanisms) must be stiff enough and strong enough to tolerate a rather high gain. If too much mass is added to strengthen and stiffen these components, the reflected inertia is increased, and this would reduce the possible 'gain that could be achieved, either because of the in- ;creased inertia of the system, or the increased inertia of larger drive motors capable of handling the loads. Positioning systems have been adopted with a gain of about 2.4, producing a maximum lag of 0.333 inches.

At this gain the variation in the blade path entering and leaving the curve of the cut is small enough that the blade will track back through the cut in an acceptable 'manner.

Some of the keys to be cut have two short segments *of are that connect, as mentioned heretofore. Forty or fifty bits or characters are required by the numerical control system in order properly to program the circular interpolation system within the controls. The same amount of information must be supplied to the contouring control to produce the desired shape whether the radius being cut is large or small, and without re gard to the length of the arc. Even though the tape readers run at 300 characters per second, they do not read information into the controls fast enough to allow the saw to make two of these short arcs, one immediately behind the other, at the speed in which the equip- 5132 character buffer storage, to store more than enough information to make several short segments of 'arc. Sufficient information is read into the buffer storage while a machine is making fairly long straight cuts to allow the machine to contour without having to wait for the tape. The short curves in question may require as many as 40 characters each, but are followed by at least two straight line moves that require only 6 or 7 characters each, well within the capabilities of the 132 'bit or character buffer storage.

The buffer storage can be eliminated as in FIG. 4, al-

beit at high cost, by utilization of a memory disc or a mini-computer to supply the control information. The information can be read out at any desired rate, far faster than the tape readout, whereby the information "can be 'applied direct to the main logic system without requiring the buffer storage. The less'expensive layout, in accordance with FIG. 3,

'utilizes'punched tape for information stora'ge'The saw 'is programmed to'cut curves by a method developed to cut a helix on a machine tool. in this type of program thetool is in the -X and'Y axis (through circular interpolatiohlfand the Zaxis motion is coordinated with a circular motion in X and Y to produce a proportionally straight line motion'in' Z, perpendicular to X and Y that will generate the desired helix. As will be understood,

slippage cannot be toleratedran'd hence the pulleys and belts illustrated for the Z axis drive comprise toothed belts or chains and complementary pulleys.

The specific recitation of X axis, Y axis' and Zaxis is arbitrary. For example the blade twist could 'be controlled by the X axis control, and the "support table could be controlled by the Y and Z axis controls, etc. No limitation is intended as to one function being controlled by a specific axis control rather than'by some other.

The specific examples of the invention as herein shown and described are for illustrative purposes only..

Various changes will no doubt occur to those skilled in the art, and will be understood as forming a part of the present invention insofar as they fall within the spirit and scope of the appended claims.

The invention is claimed as follows:

1. Apparatus for cutting a workpiece in a predetermined pattern comprising a machine having a base and a cutting blade, a three axes numerical control system having first, second and third axis control information, a workpiece support movably supported from said base, means for moving said workpiece support in a first axis direction in accordance with first axis control information, means for moving said workpiece support in a second axis direction in accordance with second axis control information, and means for turning said cutting blade in accordance with third axis control information to maintain a cutting edge of said cutting blade facing substantially in the direction of the cut through the workpiece during a cutting operation and to maintain a non-cutting edge of said blade facing in the direction of said cut during removal of the workpiece.

2. Apparatus as set forth in claim 1 wherein said first and second axes are at right angles.

3. Cutting apparatus for performing a cutting operation on a workpiece in a predetermined pattern comprising a machine having a base and a blade, a three axes numerical control system having nominally X axis, Y axis and z axis control information, a workpiece support, a sub-support for said workpiece support, and a base from which said sub-support is mounted, said subsupport being movable on an X axis relative to said base, means acting between said base and said subsupport for moving said sub-support on said X axis in accordance with X axis control information, means acting between said sub-support and said support for moving said support in a Y axis direction relative to said base, blade engaging means for determining the angle of said blade, and means acting between said blade engaging means and said base for directing the angle of said blade in accordance with Z axis control information to maintain a cutting edge of said cutting blade facing substantially in the direction of the cut through the workpiece during a cutting operation and to maintain a non-cutting edge of said blade facing in the direction of said cut during removal of the workpiece.

4. Apparatus as set forth in claim 3 wherein the means for moving the sub-support in an X axis direction comprises an X axis motor and a screw driven thereby, the means for moving the support in a Y axis direction comprises a Y axis motor and a screw driven thereby, and the means for moving the blade engaging means comprises a Z axis motor and rotary motion transmitting means between said motor and said blade engaging means.

5. Apparatus as set forth in claim 4 wherein the subsupport is supported from the base by means of ways base and a blade, a three axes numerical control system having first, second and third axis information, means for moving said workpiece support in a second axis direction in accordance with second axis control infor-- mation, guide means for said blade, and means for turning said guide means relative to said base to twist said blade in accordance with third axis control information to maintain a cutting edge of said cutting blade facing substantially in the direction of the cut through the workpiece during a cutting operation and to maintain a noncutting edge of said blade facing in the direction of said cut during removal of the workpiece.

7. Bandsawing apparatus as set forth in claim 6 wherein the numerical control system comprises a tape reader and a buffer storage receiving character information from said tape reader.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION P t n 3.908 723 Dated SEPTEMBER an 1q7s Inv n ROBERT S. HILL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 58, "4 5 should be -45- Col. 2, line 62, after "16" insert --being-- Col. 5, line 47, "pro o blem" should be --problem- Col. 7, line 16, "Ban sawing" should be --Ban sawing-- Signed and Scaled this A ttes t:

RUTH C. MASON C. MAR Arresting Offi SHALL DANN nmnzissiuner oj'latents and Trademarks

Claims

3. Cutting apparatus for performing a cutting operation on a workpiece in a predetermined pattern comprising a machine having a base and a blade, a three axes numerical control system having nominally X axis, Y axis and z axis control information, a workpiece support, a sub-support for said workpiece support, and a base from which said sub-support is mounted, said sub-support being movable on an X axis relative to said base, means acting between said base and said sub-support for moving said sub-support on said X axis in accordance with X axis control information, means acting between said sub-support and said support for moving said support in a Y axis direction relative to said base, blade engaging means for determining the angle of said blade, and means acting between said blade engaging means and said base for directing the angle of said blade in accordance with Z axis control information to maintain a cutting edge of said cutting blade facing substantially in the direction of the cut through the workpiece during a cutting operation and to maintain a non-cutting edge of said blade facing in the direction of said cut during removal of the workpiece.

5. Apparatus as set forth in claim 4 wherein the sub-support is supported from the base by means of ways and bearings, and wherein the support is supported from the sub-support by means of ways and bearings.

6. Bansawing apparatus for sawing a workpiece in a predetermined pattern comprising a bandsaw having a base and a blade, a three axes numerical control system having first, second and third axis information, means for moving said workpiece support in a second axis direction in accordance with second axis control information, guide means for said blade, and means for turning said guide means relative to said base to twist said blade in accordance with third axis control information to maintain a cutting edge of said cutting blade facing substantially in the direction of the cut through the workpiece during a cutting operation and to maintain a noncutting edge of said blade facing in the direction of said cut during removal of the workpiece.