Wire state of use indication apparatus for traveling-wire electroerosion machines
FIELD OF THE INVENTION 
     The present invention relates to traveling-wire electroerosion cutting machines and, more particularly, to a wire state of use indication apparatus for use with such a machine. 
     BACKGROUND OF THE INVENTION 
     A traveling-wire electroerosion machine commonly makes use of a continuous electrode wire stored in a wire storage means. The term &#34;wire&#34; is commonly used in the art and hence will be used herein as well to refer to a metallic or other conductive wire, ribbon, filament or tape designed to constitute a continuous traveling tool electrode in the electroerosion cutting system. The electrode wire is mounted on the machine so as to extend continuously between the wire storage means and a wire takeup means through a cutting zone along a predetermined path of wire travel. A wire traction means is commonly provided to continuously draw or pull the electrode wire out of the wire storage means and thus to continuously feed it to travel through the cutting zone and eventually to be collected onto the wire takeup means for disposal. A wire braking means is also provided to maintain taut the electrode wire traveling between the wire storage means and the wire takeup means along the path. 
     A workpiece is disposed in the cutting zone so as to be traversed by the traveling electrode wire. A machining fluid, typically distilled water, is supplied to the cutting zone while electrical machining current is passed between the traveling electrode wire and the workpiece to electroerosively remove material from the workpiece. As material removal continues, the workpiece is displaced relative to the traveling electrode wire generally transversely thereto along a predetermined cutting path to form a desired cut in the workpiece. 
     The electrode wire for use with an electroerosion cutting machine as described is commercially available in the form of a supply of the wire having a given length which is, say, wound on a reel. The wire is progressively unwound and consumed as cutting proceeds in a given electroerosion cutting operation. It is convenient and indeed desirable if the machine operator can be made aware of the amount of the electrode wire remaining on the reel at given time, or at each instant of time while the cutting is being carried out. Alternatively, the operator would desirably be advised of the noticed of the time period of cutting period available before the amount of the electrode wire remaining on the reel at such instant is used up. 
     It has been recognized that notice of such period cannot be given simply because the amount or the cutting period remaining cannot accurately be determined from the cutting period which has elapsed up to each instant during a given cutting operation. In general, in the traveling-wire electroerosion cutting process the rate of travel of the electrode wire or of with drawing the wire from the reel is caused to vary controlledly according to varying conditions in the cutting zone and also to the varying thickness of the workpiece traversed by the traveling electrode wire. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention, therefore, seeks to provide a wire state of use indication apparatus for a traveling-wire electroerosion cutting machine, which apparatus is capable of reliably and accurately indicating the remaining amount of the electrode wire and/or the remaining period for cutting as described. Another object is to provide an apparatus of the type described which is capable of alerting the machine operator when the amount of the electrode wire on the reel is about to be used up. 
     SUMMARY OF THE INVENTION 
     The invention is based upon the recognition of the fact that in the path of wire travel of a traveling-wire electroerosion machine as described there are or can be disposed one or more rollers which are rotated with the electrode wire traveling in bearing contact therewith. Such rollers should preferably be rollers which constitute capstan and pinch rollers serving as the wire braking means and disposed between the wire storage and the cutting zone. Alternatively, they may be rollers which constitute capstan and pinch rollers serving as the wire traction means and disposed between the cutting zone and the wire takeup means. Of course, any one or more further rotatable rollers may be disposed along the path of wire travel. 
     Briefly, a wire state of use indication apparatus constructed according to the invention for use in a traveling-wire electroersion cutting machine as described comprises means (a) responsive to the rotation of one such roller and including means (a1) for producing a sensing signal representing the cumulative number of revolutions of the said one roller which number, in turn, represents generally the amount of the electrode wire which has been withdrawn from the storage means, at an instant of time during the cutting operation since the commencement thereof; means (b) for having an input signal set therein generally representing the amount of the electrode wire stored in the storage means prior to the commencement of the cutting operation; and means (c) connected to means (a) and (b) and including means (c1) for processing said sensing signal with said input signal to produce an output signal representing the amount of the electrode wire remaining in the wire storage means at the said instant of time. Advantageously, means (d) is provided for displaying, substantially concurrently with the said instant of time, the said output signal in numerical form representing the said remaining amount of the electrode wire. The said remaining amount may be displayed the form of a unit of weight or length. Preferably, means (e) is associated with means (c) and operable to produce an alarm signal for alerting the operator of the machine when the said remaining amount of the electrode wire reaches a predetermined minimum value. 
     According to a further feature of the invention, means (a) further includes means (a2) for producing a further sensing signal representing the rate of rotation of the said one roller which rate in turn represents the rate of withdrawing the electrode wire from the wire storage means at the said instant of time, and means (c) further includes means (c2) responsive to the output signal and the further sensing signal for producing a further output signal representing a maximum period for which the cutting operation is allowed to continue substantially with the said remaining amount of the electrode wire. Advantageously, means (d&#39;) is provided for displaying the further output signal in a numerical form representing the said period of time. Preferably, means (e&#39;) is associated with means (c) and operable to produce an alarm signal for alerting the operator when the said period is reduced to a predetermined minimum value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     These and other features of the present invention as well as advantages thereof will become more readily apparent from the following description when taken with reference to the accompanying drawing in which: 
     FIG. 1 is an elevational view diagarammatically illustrating a traveling-wire electroerosion cutting machine having a display as a part of an apparatus according to the invention and; 
     FIG. 2 is a schematic view, essentially in a block-diagram form, illustrating a combination of means constituting an apparatus according to the invention. 
    
    
     SPECIFIC DESCRIPTION 
     Referring now to FIG. 1, the traveling-wire electroerosion cutting machine is generally designated at 1 and makes use of a continuous electrode wire 2 which is withdrawn from or pulled out of a wire supply reel 3. The reel 3 has, prior to a given machining operation, a storage of the electrode wire of a length which is known if the reel is a new wire storage reel furnished from its supplier or has a wire storage partly consumed in a previous machining operation conducted on the machine and utilizing an apparatus of the invention as will be described. 
     The electrode wire 2 released from the wire storage reel 3 is shown as extending continuously between the reel 3 and a wire takeup reel 4 through a cutting zone 5 in which a workpiece 6 is disposed. The workpiece 6 is carried on a worktable 7 which is typically displaceable by a pair of motors (not shown) to displace the workpiece 6 in a horizontal plane. The worktable 7 is movably supported by a stand 8 securely mounted on a bed 9 of the machine 1. The wire supply reel 3 and the wire takeup reel 4 are rotatably mounted on a machine column 10 standing upright and securely mounted on the bed 9. Extending from the column 10 are parallel arms 11 and 12 of which the upper arm 11 has a downward extension 13 at its end portion. The cutting zone 5 is defined between guide roller 14 and 15 secured to the downward extension 13 of the upper arm 11 and the end portion of the lower arm 12, respectively. 
     A roller set of a capstan 16 and a pinch roller 17 is disposed downstream of the guide roller 15 and, with the capstan 16 driven by a motor (not shown), serves as wire traction means for continuously withdrawing or pulling the electrode wire 2 out of the storage reel 3 to feed it to travel through the cutting zone 5 and eventually to be collected onto the wire takeup means 4 in an electroerosion cutting operation. A roller set of a capstan 18 and pinch roller 19 is disposed between the storage reel 3 and the guide roller 14 in the path of wire travel and, with the capstan 18 driven by a motor (not shown), serves as wire braking means for maintaining taut the electrode wire traveling between the storage reel 3 and the takeup reel 4 along the path of wire travel. Further rolls or rollers 20 are also provided to properly guide the electrode wire 2 to travel along the said path. A display panel 21 is shown also attached to the column 21 of the machine for displaying in numerical form a wire state of use signal produced in the apparatus as will be described. 
     The wire state of use indication apparatus embodying the invention is generally designated at 22 in FIG. 2. The apparatus comprises a sensing unit 23, a setting unit 24, a processing (computing) unit 25 and the display panel 21. 
     The sensing unit 23 is here designed to sense the rotation of one of the capstan 18 and the pinch roller 19 rotated about axes 18a and 19a respectively and serving as the wire braking means, but may sense the rotation of one of the capstan 16 and the pinch roller 17 or of any other roller disposed in the said path and rotated by the electrode wire 2 in bearing contact therewith. 
     The sensing unit 23 has a sub-unit 23a including an encoder (not shown) for sensing the number of revolutions of the capstan 18 or roller, 19. A signal representing the number of rotation is used in the sensing unit 23a including a counter to derive, at a given or at each instant of, time during the cutting operation, a signal representing the cumulative number of revolutions of the roller up to that time instant since the commencement of the cutting operation. It will be seen that this cumulative number is proportional to the amount of the electrode wire 2 which has been withdrawn from or pulled out of the storage reel 3 at that instant during the cutting operation. Prior to the commencement of the cutting operation, a start input is applied at the setting unit 24 to clear all counts previously accumulated in the counter. 
     The setting unit 24 has an input signal previously stored therein which represents the amount of the electrode wire stored on the reel 3 prior to the commencement of the cutting operation. The input signal and the signal from the sensing sub-unit 23a are combined by the processing circuit 25 to produce an output signal which represents the amount of the electrode wire remaining stored on the reel 3 at that instant. The display 21 is operated, substantially concurrently with that instant, to display the output signal in numerical form representing that remaining amount of the electrode wire 2, which amount may be displayed as a weight (e.g. grams) or length unit (e.g. meters). 
     The sensing unit 23 may also have a sub-unit 23b including an encoder (not shown) for sensing the rate of rotation of the roller 18, 19. It will be seen that the rate of rotation is proportional to the instantaneous rate of withdrawing the electrode wire from the storage reel 3 and, by combining the input signal from the setting unit 24 (representing the amount of the electrode wire 2 stored on the reel 3 prior to the commencement of the cutting operation), the output signal from the sensing sub-unit 23a (representing that remaining amount of the electrode wire) and the output signal from the sensing sub-unit 23b (representing the instantaneous rate of rotation of the roller) in the processing unit 25, there results an output signal which represents a maximum time period for which the cutting operation can be continued with that remaining amount of the electrode wire. The display 21 is operated, substantially concurrently with the said instant of time, to display that remaining period in a numerical form. The period is displayed in a unit of hours or minutes. 
     The apparatus 22 may also include an alarm unit 26 associated with an output of the processing unit 25 to provide an audible and or visible signal for alerting the operator therewith when the remaining amount of the electrode wire or the remaining time period is reduced to a predetermined minimum level. 
     The display 21 may be operated on an instantaneous basis or an instantaneous mode while the sensing unit 23 and the processing unit 25 is operating instantaneously. Accordingly, the operator can be kept, at all times, informed visibly of the remaining amount of the electrode wire or the remaining time period for which a given cutting operation is allowed to be continued with the remaining amount of the electrode wire. Thus, if the wire stored on the reel 3 is found to be insufficient after a cutting operation is commenced, he can interrupt the operation to replace the reel by a storage reel containing an adequate amount of wire. Also, by operation to replace a proper storage reel therefor. Also, by virtue of the provision of the alarm unit 26, the operator is alerted to interrupt the cutting operation when necessary. Furthermore, the operator can, at the end of a given cutting operation, ascertain conveniently the precise, amount of the electrode wire precisely remaining on the reel for one or more subsequent cutting operations.