APPARATUS FOR DRIVING AND CONTROLLING WIRE IN WIRE SAW

Abstract: Improvement of the wire saw comprising a plurality of guide rollers around which a single continuous wire (W) extending from a feed spool (21) to a take-up spool (22) is wound a plurality of times to form a sawing wire array (10) and means for absorbing slacks caused by reciprocal movement to-and-fro of said wire array (10) driven by a reversible servo-motor (11M) which is formed by two pairs of pulley assemblies (41a, 42a) so that each one of said pair of pulley assemblies is mounted on the machine frame for rotation while the other is adapted to be movable toward and apart from said stationary pulley assembly (41a) according to another reversible servo-motor (45M) for the slack absorbing, in which said separate two motors are controlled by a synchronous control circuit according to informations regarding respective rotation patterns stored and to be stored therein.

Description: BACKGROUND OF THE INVENTION The invention relates to an apparatus for driving and controlling a single continuous wire in a wire saw comprising a machine frame; a feed spool and a take-up spool respectively mounted on said machine frame for rotation between which said wire is extended; a plurality of guide rollers mounted on said machine frame in parallel to one another for rotation, around which said wire is wound a plurality of times to form a wire array which is reciprocally movable forward and backward for cutting a work piece to be urged thereto; and means arranged between said spools and said wire array for absorbing wire slacks to be caused by said cutting movement of the wire array. The wire saws of the type referred to above are in public knowledge, for instance according to U.S. Patents 3,841,297 and 3,942,508, issued respectively on October 15, 1974 and March 9, 1976. However, in the former the means for absorbing slacks is formed by a pair of pulley assemblies respectively mounted on a carriage at the opposite ends thereof for free rotation and other two pulley assemblies around which a fresh wire run extended from the wire feed spool to the wire array to be reciprocally moved for cutting and a used wire run extended from said cutting wire array to the take-up spool are respectively wound a pulurality of times so as to form a pair of wire arrays for the fresh wire run and for the used wire run in the fashion of a block and tackle, whereby said carriage may be movable toward and apart from one of said other two pulley assemblies for absorbing slacks formed reciprocally in said fresh and used wire runs due to reciprocal movement for cutting of said wire array. At the opposite ends of the carriage moved to-and-fro, there are provided a pair of switches to be actuated by contacting with said carriage for reversing the direction of rotation of the motor for driving said cutting wire array. Said wire saw is, however, not satisfactory in that since said slack absorbing means is in the form of the block and tackle like mechanism to be synchronized with the cutting wire array movement, the wire portion, above all the used and consequently worn wire portion is apt to be damaged or broken in the worst case curing pulling said mechanical absorbing means. This tendency is made larger as the number of wire wound around each pair of wire array is increased. Different from the machine disclosed in the former U.S. Patent, the slack absorbing mechanism in the latter is driven not by the wire itself but by a driving shaft from the motor which is for driving the sawing wire array so that the disadvantage referred to above can be avoided. However, synchronization of said slack absorbing mechanism with the sawing wire array is made according to a complex mechanical gearings. The wear of various elements of said gearings causes adverse affects on reciprocal movement of the sawing wire array and rotation of the guide rollers therefor which adversely affects on precise cutting. Thus such gearings must be always in careful maintenance. As well known to those skilled in the art, the guide rollers for the sawing wire array are worn by the wire applied with abrasive particle slurry so as to be inevitably reworked every after the lapse of some working time, whereby the diameter thereof is reduced little by little. Thus, concerned parts of the mechanical gearings for said synchronization must be replaced with those prepared in advance in order to keep precise working. SUMMARY OF THE INVENTION Thus, it is an object to provide an improved wire saw capable of avoiding or overcoming the defects referred to above. It is the other object of the invention to provide means for driving and controlling wire in the wire saw so as to synchronize the reciprocal movement of the sawing wire array and the reciprocal see-saw movement of the wire array for absorbing slacks caused by said sawing movement without necessity of said maintenance and exchange the concerned parts despite of inevitable reworking of the guide rollers of the sawing wire array. Said objects and other advantageous effects can be attained according to the invention by the improvement in that a reversible motor is provided for driving one of said guide rollers to generate reciprocal movement of said wire array; that said absorbing means is formed by two pairs of pulley assemblies around each pair of which a fresh wire run extending from said feed spool to said cutting wire array and a used wire run extending from said cutting wire array to said take-up spool are respectively wound a plurality of times corresponding to the number of pulleys forming respective assembly, one of said each pair of pulley assemblies being mounted on said machine frame for rotation, while the other pulley assembly of said each pair is adapted to be floatingly movable reciprocally towards and apart from the counterpart stationary pulley assembly for absorbing said slacks; that another reversible motor is provided so as to cause said reciprocal movement of said floating pulley assemblies; and that a synchronous control circuit is provided so as to control and synchronize said two reversible motors according to informations on rotation pattern stored therein respectively through a pair of servo-driver means. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in more detail in reference to the accompanying drawings, in which; Fig. 1 is a schematic respective view arrangement of essential parts of an embodiment of the wire saw to which the improvement of the invention is applied, Fig. 2 is a diagram explaining operation thereof, Fig. 3 is a diagram illustrating patterns of reciprocal movement of the slacks absorbing means or of revolution of the reversible servo-motor for driving thereof, and Fig. 4 is a diagram illustrating patterns of reciprocal movement of the sawing wire array or of revolution of the other reversible servo-motor for driving thereof, DESCRIPTION OF THE PREFERRED EMBODIMENT In Fig. 1, a wire array represented generally by 10 is formed by a single continuous wire W wound around a plurality of ("three" in the illustrated embodiment) guide rollers 11, 12 and 13, which are parallelly arranged to one another and mounted on a machine frame not shown for rotation, a number of times ("nine" times in the illustrated embodiment) with leaving a desired space between every adjacent runs of the wire W. Said guide roller 11 is drivingly rotated by a reversible servo-motor 11M so that the wire array for sawing is formed by nine runs of wire extended between the other two freely rotatable guide rollers 12 and 13. When a work piece WP set on a work bed WB is urged against said sawing wire array reciprocally moved by said reversible motor 11M for sawing with applying abrasive powder slurry thereto, said work piece WP is cut to be in ten pieces respectively of desired thickness. One end of the single continuous wire wound around said guide rollers is started from a feed spool 21, while the other end thereof is received by a take-up spool 22. Said spools 21 and 22 are driven by respective servo-motors 21M and 22M to rotate respectively in such a direction as to feed a new wire portion W₁ little by little to the sawing wire array 10 and take-up an old wire portion W2 correspondingly from said wire array 10 to maintain a constant tension along the wire W for assuring efficient and precise cutting. In the way of new wire run W₁ and old wire run W₂, there is provided respecitvely means for keeping tension in the wire W, represented generally by 30 which may be formed e.g. by an arm lever 31 (32) pivot ed on the machine frame at one end thereof for angular movement and having a pulley 33 (34) mounted at the other end for free rotation, which is arranged between a pair of guide pulleys respectively mounted also for free rotation on the machine frame not shown, said arm lever being urged by spring means 35 (36) so that said floating pulley 33 (34) may move apart from said pair of guide pulleys. Thus, the wire run W₁ (W₂) extending around one of said pair of guide pulleys, said floating pulley 33 (34) and then the other guide pulley is kept in tension owing to the force of said spring means 35 (36) urging the arm lever 31 (32) and consequently said floating pulley 33 (34) mounted thereon. There is provided a detector 37 (38) so as to detect the angular movement of said arm lever 31 (32). It goes without saying that in order to cause renewal of the single continuous wire W in the sawing wire array 10, or in other words in order to allow feeding new wire portion W₁ little by little thereinto and consequently taking-up used wire portion W₂ therefrom, the reciproval forward and backward movement of the wire array 10 and consequently the revolution of the reversible motor 11M in one direction and in the other direction must be made differential. In the illustrated embodiment, when the servo-motor 11M is rotated in the counterclockwise direction, the wire portion W₁ is pulled into the wire array 10. Thus, the motor 11M must be energized so as to rotate more in the counterclockwise direction than rotation in the clockwise direction. Since the new wire portion W₁ is pulled into the wire array 10 little by little in every reciprocal movement thereof as referred to above, the floating pulley 33 is pulled up in Fig. 1 against the force of the spring 35 and the detector 37 detects the corresponding angular movement of the arm lever 31. Similarly the detector 38 detects the angular movement of the arm lever 32 in the reverse direction. The servo-motors 21M and 22M are energized in reply to such detections to feed a fresh wire run W₁ and take-up a used wire run W₂ in order to keep the single continuous wire in stable tension. When the sawing array 10 is reciprocally moved, there is inevitably caused reciprocal slackening of the wire runs W₁ and W₂ which must be absorbed or compensated in order to keep the single wire in stable tension. In the way of new wire run W₁ and old wire run W₂, there is provided means for absorbing such slack reciprocally caused in wire runs W₁ and W₂ represented generally by 40, which is formed according to the invention by a pair of pulley assemblies, consisting of six pulleys in the illustrated embodiment, 41a, 41b (42a, 42b), a toothed rack 43 (44) mounted on the latter pulley assembly, and a pinion 45 arranged between said toothed racks 43, 44 to meshingly engage therewith and driven by a reversible servo-motor 45M via a reduction gearing 45G. Said pulley assembly 41a (42a) is mounted on the machine frame for free rotation, but the other pulley assembly 41b (42b) is floatingly movable towards or apart from the counterpart stationary pulley assembly 41a (42a) owing to wire W₁ (W₂) extending around said pair of pulley assemblies, six times in the illustrated embodiment, so as to form a wire array therebetween. It will be preferable that each floating pulley assembly 41b (42b) is engaged with a pair of guide slots formed in the machine frame not shown at the opposite ends thereof. Thus, when said motor 45M is energized to rotate the pinion 45 in the counterclockwise direction in Fig. 1, said toothed rack 43 and consequently said floating pulley assembly 41b is moved apart from the stationary pulley assembly 41a so as to absorb slack of new wire run W₁ which is caused by the movement of the sawing wire array formed between the guide rollers 12 and 13 to the right side in Fig. 1, but the toothed rack 44 and consequently said floating pulley assembly 42b is moved towards the cou nterpart stationary pulley assembly 42a so as to allow a corresponding length of the old wire portion W₂ to be pulled into the sawing wire array 10 for assuring stable and uniform tension in the single continuous wire W. Since the reversible servo-motor 11M for reciprocatingly driving the sawing wire array 10 forward and backward and the reversible servo-motor 45M for driving the means 40 for absorbing the reciprocal slack of the wire portions W₁ and W₂ are separately provided according to the invention different from the prior art in which the both is mechanically synchronized, a system for controlling and synchronizedly energizing said two motors must be provided which is illustrated in Fig. 2. In Fig. 2 wherein the same member is represented by the same referential numeral, a synchronous controll circuit SCC gives commands through a servo-driver SDI to said motor 45M and through another servo-driver SDII to said motor 11M. The motor 45M must be energized to reciprocally rotate in the opposite directions so as to move the toothed racks 43 (44) and consequently the floating pulley assembly 41b (42b) reciprocally towards and apart from the stationary pulley assembly 41a (42a) synchronously with the forward and backward movement of the sawing wire array 10 which is caused by the motor 11M. The command to be given to the motor 45M is to be as follows. In reference to Fig. 3 in which the ordinate represents revolution speed of the motor 45M per time (t) which corresponds to the speed of the upward and downward movement of the floating pulley assemblies 41b, 42b, and consequently a curve V (or V′) represents movement pattern of the motor 45M and consequently of said floating pulley assemblies, areas (a), (b), (c) (d), (e) and (f) respectively represents "accelerated upward movement", "constant speed upward movement", "decelerated upward movement", "accelerated downward movement", "constant speed downward movement" and "decelerated downward movement" of the floating pulley assembly 41b (42b) to complete one cycle movement pattern V, in respect of which (t1) is a half cycle thereof. In other words, the motor 45M is energized to start accelerated rotation in one direction (a), to rotate at a constant speed (b), to begin decelerated rotation to stop (c), to start accelerated rotation in the opposite direction (d), to rotate at a constant speed (e), and to begin decelerated rotation to stop (f). The reciprocal upward and downward movement of the floating pulley assembly 41b (42b) or the reciprocal revolution of the motor 45M in opposite directions is not limited to such pattern V, which may be replaced with another movement pattern V′ wherein the movement of the floating pulley assembly or the revolution of the motor at a constant speed is longer than that in the pattern V. The half cycle (t1) for the pattern V is shorter than the half cycle (t2) for the pattern V′. The hatched area of the curve V, however, must be equal to the hatched area of the curve V′ because said hatched area means a length of wire W₁ or W₂ to be absorbed in said zone 40 which corresponds to the stroke of the shifted wire array 10. If the quantity of the wire shift which corresponds to said hatched area and the degrees of acceleration and deceleration which corresponds to the up and down slopes of the curves are previously stored in the synchronous control circuit SCC as constants, the electronic circuit SCC may form a curve pattern or a pattern of the motor revolution by imputting a desired number of cycle per a time unit e.g. a minute and gives the corresponding command to the reversible servo-motor 45M via the servo-driver SDI. Now in reference to Fig. 4 which shows movement pattern of the wire array 10 or revolution pattern of the reversible servo-motor 11M. The wire array 10 must be reciprocally moved similar to the slack absorbing zone 40, or rather the latter must be driven similar to the for mer. When a desired cycle number per minute is inputted in the circuit SCC to form the curve or movement pattern V, the corresponding command is given therefrom to the motor 11M via the servo-driver SDII. However, the reciprocal forward and backward movements of the sawing wire array 10 must be made diferrential as referred above in order to renew the wire portion in said cutting wire array zone 10 by feeding a fresh wire portion W₁ little by little in lieu of the used wire portion W₂ worn by sawing operation. Thus, the movement of the wire array 10 in the cutting zone in one direction must be made larger than that in the other direction by a length X so as to pull new wire portion W₁ of said length X thereinto in every one cycle movement. Thus, the command from the circuit SCC to be given to the reversible servo-motor 11M is of such as driving in one direction according to the pattern V but in the other direction according to the pattern W (X + X). For the convenience of explanation, the movement pattern has been illustrated as a trapezoid, but it is not limited thereto and may be various e.g. a sine curve.

Claims: 1. In a wire saw comprising a machine frame; a feed spool and a take-up spool respectively mounted on said machine frame for rotation between which a single continuous wire is extended; a plurality of guide rollers mounted on said machine frame in parallel to one another for rotation, around which said wire is wound a plurality of times to form a wire array which is reciprocally movable forward and backward for cutting a work piece to be urged thereto; and means arranged between said spools and said wire array for absorbing wire slacks to be caused by said cutting movement of the wire array, an improvement characterized in that a reversible motor is provided for driving one of said guide rollers to generate reciprocal movement of said wire array; that said absorbing means is formed by two pairs of pulley assemblies around each pair of which a fresh wire run extending from said feed spool to said cutting wire array and a used wire run extending from said cutting wire array to said take-up spool are respectively wound a plurality of times corresponding to the number of pulleys forming respective assembly, one of said each pair of pulley assemblies being mounted on said machine frame for rotation, while the other pulley assembly of said each pair is adapted to be floatingly movable reciprocally towards and apart from the counterpart stationary pulley assembly for absorbing said slacks; that another reversible motor is provided so as to cause said reciprocal movement of said floating pulley assemblies; and that a synchronous control circuit is provided so as to control and synchronize said two reversible motors according to informations on rotation pattern stored therein respectively through a pair of servo-driver means. 2. The improvement according to Claim 1, characterized in that said means for absorbing wire slacks comprises a pair of toothed racks each fixed to each of said floating pulley assemblies and a pinion arranged between said two toothed racks to meshingly engage therewith and driven by said second reversible motor so as to cause reciprocal up and down movement of said floating pulley assemblies. 3. The improvement according to Claim 1, characterized in that said informations comprise an additional one necessary for rotating said first reversible motor more in one direction than in the other direction so as to pull a length of the fresh wire run into said cutting wire array in every reciprocal movement thereof to be given through the concerned servo-driver means. 4. The improvement according to Claim 1, characterized in that there are provided a pair of arm levers respectively pivoted on said machine frame for angular movement and having a pulley mounted thereon at the free end for free rotation, each of which is arranged between a pair of idler pullies, and that each of said fresh and used wire runs is wound around one of said idler pulleys, said lever pulley and then the other idler pulley so that by providing means for resiliently urging said arm lever said lever pulley is urged to be apart from said idler pulleys, whereby each of said wire runs is kept in tension. 5. The improvement according to Claim 3, characterized by providing a pair of detectors so as to detect angular movement of each arm lever and a pair of motors respectively driving said feed and take-up spools to rotate for supplying fresh wire run and receiving used wire run according to informations detected by said detectors.

Inventors: KUDO, MICHIO, MIYANISHI, HIDEKI
Applicants: KABUSHIKI KAISHA YASUNAGA TEKKOSHO, YASUNAGA ENGINEERING KABUSHIKI KAISHA
Application year: 1987
Main classification: B28D1
IPC codes: B24B27, B23D57, B28D5