several illustrative embodiments of the present invention will now be described with reference to the drawings . fig2 illustrates a wirecut electrical discharge machine according to a first embodiment of the present invention . referring to fig2 the elements of the wirecut electrical discharge machine are shown , namely , a workpiece 1 , a wire electrode 2 for machining the workpiece 1 , a wire bobbin 3 around which the wire electrode 2 is spooled , a torque motor 4 mounted on the shaft of the wire bobbin 3 , brake rollers 5a and 5b for applying tension on the wire electrode 2 , a brake motor 6 directly connected with the brake roller 5a , a tachometer 7 for detecting the speed of the brake motor 6 , an upper pulley 8 for supporting the wire electrode 2 above the workpiece 1 and changing the running direction thereof , a lower pulley 9 for supporting the wire electrode 2 under the workpiece 1 and changing the running direction thereof , wire electrode pinch roller 10a and take up roller 10b for running the wire electrode 2 , a constant - speed motor 11 directly connected with the wire electrode pinch roller 10a , a numerical control unit 12 ( hereinafter &# 34 ; nc unit &# 34 ;) for providing tension and running speed command values for the wire electrode 2 , a comparator 13 for comparing the output of the tachometer 7 and the speed command value of the wire electrode 2 provided by the nc unit 12 , an amplifier 14 for matching the characteristic of the output the tachometer 7 and that of the speed command value for the wire electrode 2 provided by the nc unit 12 , a compensator 15 for compensating for the tension command value for the wire electrode 2 provided by the nc unit 12 in accordance with the output of the comparator 13 , and a filter 16 for removing a direct - current ( dc ) component from the output of the comparator 13 . the operation of the wirecut electrical discharge machine configured as described above according to the first embodiment of the present invention will now be described . the wire electrode 2 , which is spooled off the wire bobbin 3 , passes between the pair of brake rollers 5a and 5b where tension is applied . the brake rollers 5a and 5b together with the brake motor 6 form a braking section of the machine . the braking section applies tension to the wire electrode 2 . after passing through the brake rollers 5a and 5b , the running direction of the wire electrode 2 is then changed by the upper pulley 8 which is placed above the workpiece 1 . as a result , the wire electrode 2 is supplied to a machining area where the workpiece 1 can be machined . the running direction is again changed by the lower pulley 9 placed under the workpiece 1 . finally , the wire electrode 2 is wound around pinch roller 10a and take up roller 10b which act to pull the wire electrode 2 through the machine . the pinch roller 10a and take up roller 10b , together with the constant - speed motor 11 , form a wire receiving section . the wire bobbin 3 is coupled to the torque motor 4 to apply tension of approximately 200 grams on the wire electrode 2 so that the wire electrode 2 does not slack between the wire bobbin 3 and the brake rollers 5a and 5b . the brake roller 5a is coupled to the brake motor 6 to apply tension to the wire electrode 2 in the machine . the brake motor 6 controls the torque with which the brake roller 5a moves in accordance with the tension command value provided by the nc unit 12 . the pinch roller 10a is coupled to the constant - speed motor 11 . the speed of the constant - speed motor 11 determines the running speed of the wire electrode 2 through the machine in accordance with the running speed command value provided by the nc unit 12 , e . g ., a voltage level applied to the constant - speed motor 11 . the speed of the wire electrode 2 through the braking section is detected as a voltage by the tachometer 7 which is coupled to the brake motor 6 . the output of the tachometer 7 , which includes ac and dc components , is compared by the comparator 13 with the running speed command value of the wire electrode 2 provided by the nc unit 12 . the output of the comparator 13 passes through the filter 16 where its dc component is removed . the compensator 15 then compensates the tension command value for the wire electrode 2 in accordance with the output of the filter 16 . accordingly , the dynamically varying tension can thereafter be controlled in a conventional manner . the error of the speed difference signal of the comparator 13 produced statically is removed by the filter 16 . for example , when tension is applied on the wire electrode 2 , the wire electrode 2 stretches , causing a difference between the running speed of the wire electrode 2 in the braking section and that of the wire electrode 2 in the wire recovery section , and then generating the dc component of a voltage equivalent to the difference in the comparator 13 . however , since the dc component is removed by the filter 16 , the set tension of the wire electrode 2 remains unchanged . in addition , the set tension of the wire electrode 2 remains the same if there is a difference between the output characteristic of the tachometer 7 and the running speed command value for the wire electrode 2 . further , the amplifier 14 can also be easily adjusted such that it matches the characteristics of the running speed command value provided by the nc unit 12 . fig3 illustrates an embodiment of the filter 16 . the filter 16 illustrated in fig3 is a high - pass filter which includes a resistor 20 , a capacitor 21 , and an operational amplifier 22 . fig4 is a diagram illustrating a second embodiment of the present invention . the second embodiment operates the same as the first embodiment except that the speed of the wire electrode 2 through the wire recovery section is detected directly with a tachometer 17 . the tachometer 17 is mounted on the shaft end of the constant - speed motor 11 . further , the speed of the wire electrode 2 detected by the tachometer 17 is used in the comparator 13 instead of the running speed command value from the nc unit 12 . it will be appreciated that the filter 16 is not limited to the high - pass filter illustrated in fig3 but may be any device that reduces gain in the low - frequency range , e . g ., a phase lead compensating circuit or a band - pass filter . it will also be recognized that the brake motor 6 of the braking section which is utilized to apply tension may be a dc motor , an ac motor or other braking device . moreover , the tachometer 7 employed for detecting the speed of the wire electrode 2 through the braking section may be replaced by an encoder and the output of the encoder may be converted from a frequency to a voltage , thus producing a similar effect . furthermore , whereas the speed of the wire electrode 2 in the braking section is detected through the direct connection of the brake roller 5a and the brake motor 6 , the speed of the wire electrode 2 may be detected by any other method if that speed is detected in the vicinity of the braking section . fig5 is a diagram of a wirecut electrical discharge machine according to a third embodiment of the present invention . in the third embodiment , an integrator 16 &# 39 ; and a comparator 17 are provided instead of the filter 16 which appears in the first embodiment . the integrator 16 &# 39 ; integrates the output of the comparator 13 and feeds back the result to the comparator 17 . the comparator 17 compares the output of the tachometer 7 with the output from the integrator 16 &# 39 ;, and outputs a difference signal which is supplied to the comparator 13 through the amplifier 14 . the operation of the third embodiment will now be described below , focusing on the operation of the integrator 16 &# 39 ;. fig6 is a graph illustrating operation of the integrator 16 &# 39 ; of the third embodiment . fig6 illustrates the operation of the integrator 16 &# 39 ; and shows a voltage waveform at point p in fig5 . a time period marked a in fig6 indicates a voltage waveform where there is no integrator 16 &# 39 ;, and a time period marked b indicates a voltage waveform where the integrator 16 &# 39 ; has been inserted . thus , the comparator 17 and the integrator 16 &# 39 ; operate to provide negative feedback which removes the dc component from the output of the tachometer , so that the set tension of the wire electrode 2 remains unchanged . fig7 is a graph illustrating a relationship between a tension command value and the tension of the wire electrode . the continuous line shown in fig7 indicates an ideal curve and the broken line indicates a curve achieved by the conventional machine . as clearly indicated by fig7 it is understood that the tension of the wire electrode 2 changes greatly as the tension command value for the wire electrode is increased . this phenomenon will be described with reference to fig5 and 6 . as the tension command value for the wire electrode 2 is increased where there is no integrator 16 &# 39 ;, the wire electrode elongates significantly , and at the same time , slip is produced between the wire electrode 2 and the brake rollers 5a and 5b in the braking section , which reduces the speed of the brake rollers 5a and 5b and generates a direct current ( dc ) component in the output signal of the comparator 13 . the direct current ( dc ) component causes the variations in tension of the wire electrode 2 . on the other hand , by providing the integrator 16 &# 39 ; and feeding back the output signal of the comparator 13 to the comparator 17 through the integrator 16 &# 39 ;, the output of the comparator 13 , i . e ., the speed difference signal , to be primarily controlled , is output without a dc component after a length of time equivalent to the time constant t of the integrator 16 &# 39 ; has elapsed ( see region b in fig6 ). hence , primary control is unaffected by setting the time constant to a much longer value than the cycle of the speed difference signal . namely , in the graph shown in fig7 the tension coincides with the ideal curve even when the tension command value for the wire electrode is increased . as an alternative to the structural configuration of the third embodiment illustrated in fig5 the output signal of the integrator 16 &# 39 ; can be fed back at the output of the nc unit 12 , instead of at the output of tachometer 7 , to produce the same effect . further , the second embodiment illustrated in fig4 can be used to modify the third embodiment just as it does the first embodiment . fig8 illustrates an embodiment of the integrator 16 &# 39 ;. the integrator 16 &# 39 ; illustrated in fig8 is a an integrator circuit which includes a capacitor 30 , a resistor 31 , and an operational amplifier 32 . further , although the integrator 16 &# 39 ; and the filter 16 which operate to remove the direct current component from the speed difference signal are shown as analog circuits in fig3 and 8 , such analog circuits can be replaced by digital software processing using a digital processor ( e . g ., microprocessor ) to produce the same effect . it will be apparent that the invention , as described above , will achieve a wirecut electrical discharge machine which allows the tension of a wire electrode to be stabilized , thus ensuring high - accuracy machining . many features and advantages of the invention are apparent from the detailed specification , and thus it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope thereof . further , since numerous modifications and changes will readily occur to those skilled in the art , it is not desired to limit the invention to the exact construction and operation illustrated and described , and accordingly all suitable modifications and equivalents may be resorted to as falling within the scope of the invention .