Abstract:
An object of the present invention is realizing a highly accurate synchronous control device which does not cause time lag by detecting the rotational frequency and phase simultaneously perpetually by same signal in the synchronous control of plural electric motors. The synchronous control device synchronizes accurately rotational frequency and rotation phase of an electric motor or a machine axis driven by the electric motor. A master section outputs phase signals or frequency signals based on rotational frequency reference. 
     On the other hand, a slave section detects master rotational frequency setting signals and master phase setting signals simultaneously and perpetually by using the phase signals or frequency signals from the master section, and detects rotational frequency feedback signals and phase feedback signals simultaneously and perpetually based on output of a rotary encoder attached to an electric motor or connected to an machine axis driven by the electric motor, then detects phase deviation perpetually out of the master phase setting signals and the phase feedback signals. 
     The electric motor of the slave section or the machine axis driven thereby is synchronously controlled based on the phase deviation, said master rotational frequency setting signals and said rotational frequency feedback signals. 
     Also, the master section may provide a control device for controlling the electric motor, and a means for sending frequency signals outputted from a rotary encoder attached to the electric motor or a rotary encoder connected to an machine axis driven by the electric motor to the slave section.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a synchronous control device for electric motors and machine axes driven by electric motors in a conveying device. 
     2. Description of the Related Art 
     When synchronizing a plurality of electric motors or machine axes driven by electric motors to keep the electrical phases thereof in the same relation to each other, a common rotational frequency reference is set, and correction of the synchronous control is made by using a deviation between the frequency signal corresponding to the rotational frequency reference and the frequency signal of a rotary encoder of the electric motor. 
     In the prior art, the signal formation and detecting method of the main control loop for the rotational frequency reference is independent from the correction loop for frequency deviation, so that a time lag between them occurs and highly accurate synchronous control is very difficult. 
     FIG. 7 shows a conventional synchronous control device for a plurality of electric motors, for example, two electric motors. 
     In FIG. 7, Cm is a concentrated control device of a master section. In the concentrated control device Cm, Sm is a rotational frequency setting device, Tm is an communication interface which sends out the rotational frequency setting signals from the rotational frequency setting device. The rotational frequency setting signals are sent to a slave section through a communication line  1 . 
     Fm is a frequency signal generator which inputs the rotational frequency setting signals output from the rotational frequency setting device Sm and which generates frequency signals proportional to the rotational frequency setting input. The output from Fm is sent to the slave section through a signal line  2 . Now, in the following explanation, a line which transmits signals transformed to the serial signals from the digital signals is called a communication line, and a line which sends pulse signals as they are is called a signal line. 
     Further, Cs 1  and Cs 2  are slave section control devices, As 1  and As 2  are driving devices of electric motors of the slave section, Ds 1  and Ds 2  are electric motors in the slave section, Rs 1  and Rs 2  are rotary encoders added to the electric motors, Gs 1  and Gs 2  are transmission devices, Ks 1 , Ks 2  are machine axes driven by electric motors of the slave section. 
     The slave section control device Cs 1  and Cs 2  are composed of the same components, so that, in the following explanation, only the slave section control device Cs 1  is explained, but the components of the slave section control device Cs 2  are similarly numbered. 
     In FIG. 7,  11  is a communication interface, which receives the rotational frequency setting signals output from the communication interface Tm in the master section, and stores them into the rotational frequency reference storing means  12  as the master rotational frequency setting signals.  15  is a rotational frequency feedback detector, which detects feedback rotational frequency from the frequency signals output from the rotary encoder Rs 1  in the slave. 
       13  is a frequency deviation counter, which up-counts the frequency signals from the frequency generator Fm in the master section, and detects the deviation by down-counting the frequency signals from the rotary encoder Rs 1  in the slave section. 
     These outputs of the frequency deviation counter  13  are added or substituted to the master rotational frequency setting signals output from the rotational frequency reference storing means  12  through a proportional integration amplifier  14  (in the following, referred to PI) as correction signals, further calculated with the rotational frequency feedback signals output from the rotational frequency feedback detector  15  and sent to the driving device As 1 . 
     That is, the master rotational frequency setting signals are corrected based on the output of the frequency deviation counter  13  (frequency deviation), and rotational frequency and phase of the electric motor Ds 1 , Ds 2  in the slave section Cs 1 , Cs 2  are controlled based on the deviation between said corrected rotational frequency setting signals and rotational frequency feedback signals. 
     In the conventional method, the signal formation and the detecting method of the main control loop of the rotational frequency reference and the correction loop of the frequency deviation in the slave section are different, so that the time lag is inevitable and a highly accurate synchronous control is very difficult. 
     These are explained in FIG. 8 further. 
     In FIG. 8,  1  is a reference signal which is output from the communication interface Tm in the concentrated control device of the master section Cm in FIG. 7, received and detected in the communication interface  11  set in the rotational frequency slave section control device, and stored in the rotational frequency reference storing means  12 . Further in FIG. 8,  2  is a frequency signal which is sent from the frequency generator Fm in the master section Cm in FIG. 7, and input to the frequency deviation counter  13  set in the slave section. 
     As shown in FIG. 8, the reference signal  1  and the frequency signal  2  are different in the signal form and the detecting method is also different, so that the time lag occurs although they should be overlapped in essence. 
     Moreover, in FIG. 8, times t 1 , t 2 , t 3  . . . show timings to implement synchronous control processing in the slave section. At time t 2 , corresponding to a point A of the reference signal  1 , the frequency signal  2  should agree with A′. However, the frequency signal  2  is controlled by using the value at B point, because of the time lag caused by the difference of a generated method and a transmission path between reference signal  1  and frequency signal  2 . That is, ΔF in FIG. 8 is occurred in the synchronous loop as an error in the synchronous control, so that a highly accurate synchronous control is difficult. 
     SUMMARY OF THE INVENTION 
     This invention is developed for resolving the problem. The present invention provides an accurate synchronous control without causing the time lag by detecting the rotational frequency and phase simultaneously and perpetually with the same signals in the synchronous control of a plurality of electric motors. 
     A master section outputs phase signals or frequency signals based on rotational frequency reference. A slave section detects master rotational frequency setting signals and master phase setting signals simultaneously and perpetually by using the phase signals or frequency signals from the master section, and detects rotational frequency feedback signals and phase feedback signals simultaneously and perpetually based on output of a rotary encoder attached to an electric motor or connected to an machine axis driven by the electric motor, then detects phase deviation perpetually out of the master phase setting signals and the phase feedback signals. 
     The electric motor of the slave section or the machine axis driven thereby is synchronously controlled based on the phase deviation, said master rotational frequency setting signals and said rotational frequency feedback signals. 
     Also, the master section may provide a control device for controlling the electric motor, and a means for sending frequency signals outputted from a rotary encoder attached to the electric motor or a rotary encoder connected to an machine axis driven by the electric motor to the slave section, according to the present invention. 
     The feature and advantage of the present invention will be apparent from the following mode for implementing the invention with following accompanying drawings. 
    
    
     BRIEF EXPLANATION OF THE DRAWINGS 
     FIG. 1 shows a first embodiment. 
     FIG. 2 shows a drawing explaining an action of the embodiment of the present invention. 
     FIG. 3 shows an example of components of a rotational frequency setting calculator etc of the first embodiment. 
     FIGS. 4 a  and  4   b  show drawings explaining the action of the rotational frequency setting calculator of the first embodiment. 
     FIG. 5 shows a second embodiment. 
     FIG. 6 shows a third embodiment. 
     FIG. 7 shows an example of a prior art. 
     FIG. 8 shows a drawing explaining, time lag of the rotational frequency setting and the phase setting in prior art example. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention resolves the problems in the following way. In the concentrated control device, that is a master section of the synchronous control for a plurality of electric motors, a phase detector of which input frequency is proportional to a setting rotational frequency, and rotation phase signals detected in the phase detector are always sent to the slave section. 
     The slave section receives said phase signals sent from the master section, and at any time detects simultaneously both master rotational frequency setting signals and master phase setting signals at the same time out of the sent common phase signals. 
     On the other hand, the slave section obtains rotational frequency feedback signals and phase feedback signals at the same time by perpetual detecting simultaneously both the rotational frequency feedback signals and phase feedback signals out of signals of a rotary encoder attached to the electric motor or a rotary encoder connected to a machine axis driven by the electric motor. Moreover, the slave section always calculates phase deviation between said master phase setting signals and said phase feedback signals. 
     Further the synchronous control of the electric motors is implemented based on the phase deviation, said master rotational frequency setting signals and said rotational frequency feedback signals. 
     As mentioned above, the slave section of the synchronous control device can obtain both the rotational frequency setting signals and the phase setting signals, based on the common rotation phase at the same time sent from the master section, so that a very highly accurate high synchronous control is realized. 
     In the above mentioned expression, the rotation phase signal is sent from the concentration control device, the master section, but it is also capable of using frequency signals sent from the rotary encoder, and using frequency outputting signals from the rotary encoder attached to the electric motor set in the master section or the rotary encoder connected to the machine axis driven by the electric motor. 
     In the following, the present invention is explained by referencing drawings. FIG. 1, FIGS. 4 a  and  4   b , FIG.  5  and FIG. 6 are drawings showing components of the embodiment of synchronous control device, FIG. 2 shows a process of the master section, FIG. 3 shows an embodiment of concrete components of FIG.  1 . 
     Further, FIG. 1, FIG.  5  and FIG. 6 show the synchronous control of plural electric motors of the present invention, which has a master section and two slave sections as an example for making the explanation simple, and same parts in FIG. 7 showing the conventional art have same reference numbers. 
     In FIG. 1, Cm is a concentrated control device that is a master section, Cs 1 , Cs 2  are the slave control devices, As 1  and As 2  are driving devices of electric motors of the slave section, Ds 1 , Ds 2  are electric motors of the slave section, Rs 1 , Rs 2  are encoders of an absolute system added to the electric motors or an inclement system having Z phase. Further Gs 1 , Gs 2  are transmission devices, Ks 1 , Ks 2  are machine axes rotated through Gs 1 , Gs 2  by the electric motors Ds 1 , Ds 2 . 
     Now, in the embodiment in FIG. 1, a case which the rotary encoder is attached to the electric motor is explained, but the rotary encoder is capable of being connected to the machine axis connected to the electric motor through a transmission device. 
     Next, the concentrated control device Cm of the master section in FIG. 1 is explained. 
     In the concentrated control device Cm, Sm is a rotational frequency setting device, the output is sent to the frequency generator Fm. The frequency generator Fm generates signals proportional to the rotational frequency setting input and further the frequency signal is input into a phase detector Pm. 
     The phase detector Pm has an accumulating function and it is overflowed and cleared, when counting pulse number corresponding to one rotation of the rotary encoder in the slave section. The count value of the accumulating counter is sampled at a predetermined time distance ΔT, and the phase detector Pm outputs signals corresponding to the phase signals. These phase signals are sent to the slave section control device Cs 1  through the communication line  1  by the communication interface Tm. 
     In FIG. 2, the rotational frequency setting device Sm, the frequency generator Fm, the phase detector Pm and communication interface Tm are explained further. 
     The frequency generator Fm generates the frequency signals proportional to the rotational frequency setting value by the instruction of the rotational frequency setting device Sm, and the output frequency changes as (a) in FIG.  2 . 
     The signals which the frequency generator Fm generates are counted in the accumulated counter in the phase detector Pm, and the count value of the accumulated counter changes as (b) in FIG.  2 . 
     The accumulated counter of the phase detector Pm accumulates the pulse output from the frequency generator Fm, and it is overflowed and cleared when counting pulse number corresponding to the one rotation of the rotary encoder in the slave section, so that the count value is corresponding to a rotation phase. 
     The communication interface Tm takes sampling of the count value of the accumulated counter of the phase detector at timing (at the time of the black point of (b) in FIG. 2) of time t 1 ,t 2 , . . . (time interval ΔT) and transform the counted value of the accumulation counter of the phase detector Pm shown in (c) in FIG. 2 to the serial signal, and send them to all slave sections periodically and at high rotational frequency. Now, the sending frequency (=ΔT) of the phase signal by the communication interface Tm is short practically less than 0.2 msec, for example when the rotation number of the above mentioned rotary encoder is 2400 rpm, one rotation time is 25 ms, so that the phase signal number of 125 are sent by one rotation (in FIG. 2, for simplifying the explanation, the rotation number of the phase signal by one rotation is abbreviated to 3). 
     Next, the slave section control devices Cs 1 , Cs 2  in FIG. 1 are explained. In the slave section control devices Cs 1 , Cs 2 ,  21  is a communication interface,  22  is a rotational frequency setting calculator, and  23  is phase setting detector. Further  24  is a phase signal receiver receiving the phase signal from the rotary encoder Rs 1 , Rs 2 ,  25  is a rotational frequency feedback signal detector,  26  is a phase feedback signal detector,  27  is a phase deviation calculator and  28  is a PI amplifier. 
     The communication interface  21  of FIG. 1 receives the serial signal sent from the communication interface Tm of the said master section at given timing, and restores the master phase signals shown as (c) in FIG.  2 . Further the rotational frequency setting calculator  22  calculates the master rotational frequency setting signal from the phase setting signal output from the communication interface  21 . The phase setting detector  23  stores the phase setting signals and overflows numbers (explained later) output from the communication interface  21 . 
     FIG. 3 shows the details of the communication interface  21 , the rotational frequency setting calculator  22 , the phase setting detector  23 , the phase signal receiver  24 , the rotational frequency feedback signal detector  25 , the phase feedback signal detector  26  in the FIG. 1, and FIGS. 4 a  and  4   b  calculation action of the master rotational frequency setting signal by the rotational frequency setting calculator  22 . 
     Next, the action of the rotational frequency setting calculator  22  and phase setting detector  23  are explained by the FIG.  3  and FIGS. 4 a  and  4   b.    
     As shown in FIG. 3, the communication interface  21  provides a register  21   a , and transforms the serial signals corresponding to the master phase setting signals sent through the communication line  1 ′ to the parallel signals and stores in the register  21   a.    
     The master phase setting signals stored in the register  21   a  (in the following, it is abbreviated as phase setting signals in necessary occasions) are taken sampling at an interval of time ΔT, and stored in each of the register  22   a  of the rotational frequency setting calculator  22  and the register  23   a  of the phase setting detector  23 . Now, it is preferable that the time interval ΔT is same with the time interval ΔT of the concentrated control device Cm, but, the synchronization to the sampling time of the concentrated control device Cm is not always necessary 
     Next, the calculation of the rotational frequency setting signal of the rotational frequency setting calculator  22  is explained by using FIGS. 4 a  and  4   b . FIG. 4 a  shows the master rotational frequency setting signal calculated by the rotational frequency setting calculator  22 , and FIG. 4 b  shows the phase setting signal received by the communication interface  21 . 
     As mentioned above, the phase setting signal sent from the concentrated control device Cm is the count value of the accumulation counter set in the phase detector Pm of the concentrated control device Cm, and the count value of the accumulation counter is accumulated frequency signals proportional to the rotational frequency setting value. Therefore, the variation of the count value of the accumulated counter, that is, the variation of the phase setting signal indicates signals corresponding to the rotational frequency signal. Now, the accumulation counter is cleared when counting the pulses corresponding to one rotation of the rotary encoder of the slave section, so that, when the count value of the accumulation counter, that is the phase setting signal sent from the concentrated control device Cm, is smaller than that of the last time, the accumulated counter is overflowed and cleared. 
     As mentioned above, obtaining variation ΔPk (k=1−m) of the phase setting signal and dividing by the ΔT of sampling interval shown in FIG. 4 b , the rotational frequency setting signal shown in FIG. 4 a  is obtained. Now, when the phase setting signal is less than that of the last time, the accumulated counter of the concentrated control device Cm is cleared (in the time that the accumulated counter is overflowed), so that, in this case, the above mentioned variation ΔPn+1, ΔPn+3 are obtained by obtaining the phase setting signal after ΔT on a line which is extended decline of the phase setting signal shown by dotted lines A 1 , A 2  in FIGS. 4 a  and  4   b . 
     Based on the above-mentioned principle, the rotational frequency setting calculator  22  calculates the rotational frequency setting signals as in the following. 
     The phase setting signal through communication line  1 ′ is registered in the register  22   a  of the rotational frequency setting calculator  22  each ΔT time. When the next phase signal is stored in the register  22   a  in ΔT time, the phase setting signal registered in the register  22   a  is transmitted to the register  22   b , and the newly input phase setting signal is registered in the register  22   a . As the result, the phase setting signal sampled in this time is kept in the register  22   a , and the phase setting signal sampled the last time is kept in the register  22   b.    
     ΔP calculator  22   c  obtains the variation ΔP from the phase setting signals which are kept in the registers  22   a ,  22   b  and sends it to the ΔP/ΔT calculator  22   d . The ΔP/ΔT calculator  22   d  obtains the rotational frequency setting signal by dividing the variation ΔP by the time interval ΔT. The calculated rotational frequency setting signal is kept in the register  22   e.    
     As mentioned above, the rotational frequency setting calculator  22  obtains a master rotational frequency setting signal based on one phase signal obtained from the communication interface  21 . 
     Further the phase setting detector  23  keeps the phase setting signals and stores times that the phase setting signal is less than that of the last time, that is the overflow times. Like this, the rotational frequency setting calculator  22  and the phase setting detector  23  obtain simultaneously the master rotational frequency setting signals and the master phase setting signals based on the phase setting signal sent from the concentrated control device Cm. 
     On the other hand, the phase signal receiver  24  of the slave section Cs 1 , Cs 2  receives signals from the rotary encoder Rs 1 , Rs 2 . The phase feedback signal detector  26  detects the phase signals shown as (b) in FIG. 2, which are feedbacked from the electric motor. The rotational frequency feedback signal detector  25  calculates the rotational frequency feedback signals from the electric motor Ds 1 , Da 2 . 
     As shown in FIG. 3, the rotational frequency feedback signal detector  25  and the phase feedback signal detector  26  comprise the same components with the mentioned rotational frequency setting calculator  22  and the phase setting detector  23 , and the phase receiver  24  comprises the counter  24   a  for counting pulse signals sent from the rotary encoder Rs 1 . 
     The above mentioned accumulating counter  24   a  counts the pulse signals sent from the rotary encoder Rs 1 , and when counting the pulses corresponding to the one rotation of the rotary encoder, it is overflowed and cleared. Because of this, the count value shows the rotation phase of the rotary encoder Rs 1 . 
     The count value of the accumulated counter  24   a  is taken sampling by the sampling signal of the fore mentioned time interval ΔT, and stored in the register  25   a  of the rotational frequency feedback signal detector  25  and the register  26   a  of the phase feedback signal detector  26 . 
     The rotational frequency feedback signal detector  25  works same with the rotational frequency setting calculator  22 , and calculates the rotational frequency feedback signals based on the rotation phase signals registered in the register  25   a.    
     Further, signals corresponding to the rotation phase of the rotary encoder Rs 1  is stored in the register  26   a  in the phase feedback signal detector  26 , and the overflow number of the accumulation counter  24   a  is stored in the phase feedback signal detector  26 . 
     The phase deviation calculator  27  calculates the master phase setting signals and the phase deviation of the rotary encoder Rs 1  based on the master phase setting signal output from the phase setting detector  23 , the phase feedback signal output from the phase feedback signal detector  26  and the overflow number stored in the phase setting detector  23  and the phase feedback signal detector  26 . 
     The phase deviation calculator  27  obtains the phase deviation Hs by a following equation (1) (the details of which are in U.S. application Ser. No. 09/464,890, filed Dec. 16, 1999, which is incorporated herein by reference). 
     
       
         Hs=Nmax×Covf+Cm−Cs  (1) 
       
     
     Now, Nmax is pulse numbers by one rotation of the rotary encoder Rs 1  (overflow pulse numbers of accumulation counter in the concentrated control device Cm and accumulation counter  24   a ), Covf is the difference of the overflow time of accumulation counter in the concentrated control device Cm and the accumulated counter  24   a  (1 increment by an overflow of the accumulation counter in the concentrated control device Cm and  1  subtract by an over flow of the accumulation counter  24   a ), Cm is a value kept in the register  23   a  of the phase setting detector  23 , and Cs is a value kept in the register  26   a  of the phase feedback signal detector  26 . 
     This phase deviation is added to the master rotational frequency setting signal output from the rotational frequency setting calculator  22  as the phase correction signal through the PI amplifier  28  shown in FIG. 1, and sent to the driving devices As 1 , As 2  to control the electric motors Ds 1 , Ds 2 . 
     That is, as mentioned above, the master rotational frequency setting signal is corrected based on the output of the phase deviation counter  27 , the rotational frequency and the phase of the electric motors Ds 1 , Ds 2  of the slave section control device of Cs 1 , Cs 2  are controlled by the deviation between the corrected rotational frequency setting signal and rotational frequency feedback signal. 
     As mentioned above, this invention obtains the master rotational frequency setting signal and the master phase setting signal based on one phase signal, so that the master rotational frequency setting signal and the master phase setting signal can be obtained without the time delay, and a highly accurate synchronous control is capable. 
     Now, the concentrated control device Cm of the master section and the slave section control device Cs 1 , Cs 2  in FIG.  1  and FIGS. 4 a  and  4   b  are composed of microprocessor, digital signal processor, gate array etc., so that it is needless to say that it can be processed with very high rotational frequency. 
     Further in the above mentioned embodiment, a case that the rotation direction of all electric motors in the slave section is supposed to be same, but, even if there are electric motors of an inverse rotation direction, they can be implemented synchronous control the connection of the rotary encoder and the accumulation counter  24   a , in the same manner that the rotation direction of all electric motors is same. 
     Next the second embodiment shown in FIG. 5 is explained. 
     In FIG. 5, parts having same function with those in FIG. 1 have same symbols and the explanation is neglected. 
     The present embodiment is that which the concentrated control device Cm sends the frequency signals of frequency proportional to the rotational frequency setting signals output from the frequency generator Fm to directly the slave section control device Cs 1 , Cs 2  through signal line  2 ′, and in the slave section control device Cs 1 , Cs 2  the master rotational frequency setting signal and the master phase setting signal are obtained. Now, the frequency signals are pulse signals like output signals of an absolute encoder or an incremental encoder having Z phase. 
     The components of the rotational frequency setting calculator  22 , the phase setting detector  23  in the present embodiment are same with those of in FIG. 3, but the phase setting receiver  21 ′ having an accumulation counter instead of the register, and the accumulation counter counts above-mentioned frequency signals sent from the concentrated control device Cm. Further the count value of the accumulation counter is taken sampling by the sampling signals of the time interval ΔT, and the sampling data are registered in the register  22   a  of the rotational frequency setting calculator  22  and the register  23   a  of the phase setting detector  23 . Action after this is same with the first embodiment, and the master rotational frequency setting signal is calculated by the rotational frequency setting calculator  23  like the explanation in FIG. 3, further, the phase setting signal is detected by the phase setting detector  23  at the same time with this. 
     Further the components of the phase signal receiver  24 , the rotational frequency feedback signal detector  25  and the phase feedback signal detector  26  are same with those of FIGS. 4 a  and  4   b , the synchronous control is implemented the same with the first embodiment. 
     Also, in this embodiment, as the master rotational frequency setting signal and the master phase setting signal is obtained also based on one frequency signal, the master rotational frequency setting signal and the master phase setting signal is obtained without delay time, same as the first embodiment, so that the highly accurate synchronous control is realized. 
     FIG. 6 shows the third embodiment of the present invention, and the present embodiment is that which, using a usual electric motor controlled by usual rotational frequency control as the master section, and send signals of a rotary encoder attached to the electric motor to the slave section. 
     In FIG. 6, Cm 1  is a control device of the master section, Am 1  is a driving device of the electric motor of the master section, Dm 1  is an electric motor of the master section, Rm 1  is a rotary encoder, which is attached to the electric motor, with an absolute system or an incremental system having Z-phase. Further Gm 1  is a transmission device, Km 1  is a rotating machine axis driven through the Gm 1  by the electric motor Dm 1 . 
     Also, in the control device Cm 1  of the master section,  31  is rotational frequency setting detector,  32  is rotational frequency feedback signal detector. 
     The master section is driven by the usual rotational frequency control, and the output (the same pulse output with the second example of the frequency generator Fm in the second embodiment) of the rotary encoder Rm 1  of the master section is sent to the slave section through the signal line  2 ′. 
     In the slave section control device Cs 1 , Cs 2 , the phase setting receiver  21 ′ having an accumulated counter, like explained in the second embodiment, receives the output of the rotary encoder Rm 1 . Further, like the second embodiment, the rotational frequency setting calculator  22  and the phase setting detector  23  detect simultaneously the master rotational frequency setting signals and the master phase setting signals, and control the synchronous control in the manner as the first example shown in FIG.  1 . 
     In this embodiment, as the master rotational frequency setting signal and the master phase signals are obtained from the rotary encoder Rml of the master section, the master rotational frequency setting signals and the master phase setting signals are obtained without time lag like the first embodiment and the second embodiment, so that the highly accurate synchronous control is realized. 
     As mentioned above, in the present invention, the rotational frequency setting and phase setting of the electric motor are simultaneously detected from one of the phase setting signal or frequency signal of the master section, and the synchronous control is implemented based on this, so that highly accurate setting of rotational frequency setting and phase setting without time lag is capable, and the very high highly accurate synchronous control is realized. 
     Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been changed in the details of components without departing from the spirit and the scope in the appended claims.