Abstract:
A device for positioning a workpiece for machining has a bench, which is mounted movably at a base and to which the workpiece ( 14 ) can be fastened. A detection device ( 15, 16, 17, 18 ) is arranged at the bench ( 12 ) for detecting a state of a machining process of the workpiece ( 14 ) and for generating detected information depending thereon. An energy transmission device ( 38, 42, 49, 50 ), for transmitting electric energy to the components ( 16, 17, 18, 21 ), is arranged on the bench ( 12 ). An information transmission device ( 39, 40, 43, 44, 59, 60 ) for transmitting detected information of the detection device ( 15, 16, 17, 18 ) to a control ( 63 ) is associated with the base ( 11 ). The energy transmission device ( 38, 42, 49, 50 ) transmits the energy and the information transmission device ( 39, 40, 43, 44, 59, 60 ) transmits the information inductively and/or capacitively via the same air gap. An additional detection device ( 54 ) detects a state of energy transmission and generates additional detected information depending thereon. The additional detected information is transmitted as feedback information to the control ( 63 ) for correcting disturbances and/or changes in the energy transmission device ( 38, 42, 49, 50 ) and/or of the information transmission device ( 39, 40, 43, 44, 59, 60 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of priority under 35 U.S.C. § 119 of DE 103 47 612.1 filed Oct. 11, 2003, the entire contents of which are incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention pertains to a device for positioning a workpiece for machining, with a bench, which is mounted movably on a base and to which the workpiece can be fastened, with detection means arranged at the bench for detecting a state of a machining process of the workpiece and for generating detected information depending thereon, with energy transmission means for transmitting electric energy to components arranged on the bench, and with information transmission means for transmitting detected information of the detection means to a control associated with the base.  
       BACKGROUND OF THE INVENTION  
       [0003]     During the automated machining of workpieces, these workpieces are fastened mostly on pallets and then fed to different clamping or rotary tables for the further machining. Movement of the bench relative to a stationary base is often necessary. Since a plurality of sensors, for example, inductive proximity switches, pressure sensors, temperature sensors or similar means are frequently arranged on the pallet, and since, moreover, actuators are frequently also necessary on the pallet, it is necessary to supply the components arranged on the pallets with energy, on the one hand, and, on the other hand, to transmit the information from the sensors to a central control for controlling the machining. So-called slip ring contacts are used for this purpose in most cases. These slip ring contacts have the drawback that they are subject to wear and are, in particular, readily contaminated during the machining operation. This contamination or wear may lead to disturbances and errors and even to complete failure. On the whole, the use of slip ring contacts is very maintenance-intensive. Contactless methods are sometimes also used to transmit the energy or the information. For example, optical signal transmission by means of optical light guides and infrared radiation is used. The drawback of this method is that the optical light guides of the two parts moving in relation to one another must be precisely adjusted in order for error-free transmission to be possible. In contrast, changes in the air gap between moving parts can greatly affect the quality of the signal transmission in the case of inductive signal transmission. Erroneous information may be transmitted, in particular, in case of contamination or a change of the air gap.  
       SUMMARY OF THE INVENTION  
       [0004]     The basic object of the present invention is to guarantee the transmission of energy to a mobile work bench as well as the transmission of information from the work bench to a control in a simple manner, extensively without wear and possibly error-free.  
         [0005]     The object is accomplished such that the energy transmission means and the information transmission means transmit the energy and the information in a device of the type described in the introduction inductively and/or capacitively via the same air gap; that additional detection means are provided for detecting an energy transmission state and for generating additional detected information depending thereon, and that the additional detected information is transmitted to the control as feedback information for correcting disturbances and/or changes in the energy transmission means and/or the information transmission means.  
         [0006]     The transmission of the energy as well as of the information via the same air gaps makes it possible, on the one hand, to arrange the energy transmission means and the information transmission means in the same transmission head. This results in a simple design with a small number of individual components. Since, furthermore, the information is transmitted via the same air gap as the energy, the detection of an energy transmission state, for example, of the transmitted voltage or of the power consumed, yields information on the state of the air gap in a simple manner. This information can be used as feedback information in a simple and efficient manner to correct disturbances in the information transmission. For example, a supply voltage of 24 V can thus be guaranteed in a stable manner.  
         [0007]     A common transmission head is preferably provided for the energy transmission means and the information transmission means. This results in a simple design. High resistance to contamination is achieved especially if this transmission head is encapsulated. The transmission head may have a core, on which an energy transmission coil and an information transmission coil with mutually different magnetic field orientations are arranged. The fields for the energy transmission and for the information transmission can thus be extensively separated from one another.  
         [0008]     In a variant, the additional detection means are associated with the bench and they detect a transmitted voltage. This voltage is generated by transmitting energy inductively via the air gap. As an alternative or in addition, the additional detection means may be associated with the base and detect a current or a power consumption of a supply device for the energy transmission means. Since the primary current and the power consumption of this supply device also depend on the state of the air gap, the detection of the current or of the power consumption of this supply device also provides good information on the state of the air gap. It is also possible for the additional detection means to detect the temperature of an electric circuit associated with the bench or the base. This information on the temperature of the electric circuit may also be suitable for feedback. For example, internal protocols may be set up here. Signals of an additional sensor can be used for the process control.  
         [0009]     Another variant of the present invention is characterized in that a control unit of an energy supply for the components arranged on the bench is performed by controlling a frequency of the voltage fed to the energy transmission means. This control may be performed, for example, by means of pulse width modulation. Since the energy is transmitted here similarly to the transmission by means of a transformer, the energy supply can be controlled simply and reliably by frequency control.  
         [0010]     The information transmission is preferably performed digitally. In particular, the use of a binary code is advantageous. This digital transmission is, in particular, not prone to disturbances if frequency coding of the digital values and/or of the binary values is performed. Discrete voltage levels are not to be detected in this case. It is rather sufficient for the demodulation to recognize individual frequencies. In addition, it is advantageous if the frequency assignment is selectable. This selection may be carried out especially by means of so-called jumpers. The frequency assignments used can be selected in this case depending on the ambient conditions such that the most error-free transmission possible is achieved.  
         [0011]     In a variant, demodulating means, which have logical units for the decoding, are provided for decoding the transmitted information. The individual transmitted values can thus be recognized in a simple manner by comparison with a reference frequency by the logical units and the transmitted information can thus be demodulated especially in the embodiment in which frequency coding of the digital values and/or of the binary values is performed.  
         [0012]     One variant of the present invention is characterized in that bidirectional information transmission means are provided. These bidirectional transmission means make possible, on the one hand, the detection of measured values that correspond to the machining process. However, it is also possible, on the other hand, to transmit control signals to the components on the bench for machining the workpieces, for example, to actuators arranged there.  
         [0013]     A transmission head for radial coupling or axial coupling may be used in the device according to the present invention. Lower scatter field losses occur in case of the axial couplings than with the radial coupling. However, the radial coupling makes it possible to arrange at least one transmission head of a pair of transmission heads forming a transmission section outside a pivot axis necessary for rotating the bench. In addition, it is advantageous if the decoding is performed by means of phase detection.  
         [0014]     One variant of the present invention is characterized by a carrier that can be fastened to the bench for receiving the workpiece, the detection means and/or the components, wherein the energy transmission means and/or the information transmission means also transmit the energy and/or the information inductively and/or capacitively between the bench and the carrier. The workpiece and the necessary sensors or actuators may be fastened to the carrier in this case, the carrier being placed on the bench for the machining. So-called pallets are frequently used as carriers. The replacement of the pallets is usually performed in a fully automated manner. Since energy transmission and information transmission take place reliably in this case because of the energy transmission means and information transmission means having the features of the present invention without plug-type and sliding contacts being necessary for this purpose, and without the possibility of errors in transmission because of erroneous adjustment or contamination or wear, good machining results can thus be achieved in the long term at a high speed.  
         [0015]     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a schematic view of a rotary table with the features of the present invention;  
         [0017]      FIG. 2  is a schematic view of a transmission head according to  FIG. 1 ;  
         [0018]      FIG. 3  is a section through two transmission heads facing one another;  
         [0019]      FIG. 4  is a block diagram of the transmission device according to  FIG. 1 ; and  
         [0020]      FIG. 5  is a schematic view of a rotary table as another exemplary embodiment having the features of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]      FIG. 1  shows a schematic view of a device for positioning a workpiece for machining. A rotary table  10  with a stationary base  11 , at which a bench  12  is arranged pivotably or rotatably around an axis A, is shown. A carrier  13  is fastened to the bench  12 . The carrier  13  is a so-called pallet  13 , which is fastened to the bench  12  in the known manner.  
         [0022]     A workpiece  14  is arranged for machining on the side of the pallet  13  facing away from the bench  12 . In addition, a plurality of sensors  15 ,  16 ,  17 ,  18  are arranged on the side of the pallet  13  facing away from the bench  12 . The sensor  15  is a temperature sensor  15  for determining the temperature of the workpiece  14 . The sensor  16  is a pressure sensor  16  for determining the weight or the pressing force on the workpiece  14 . The sensor  17  is a height sensor  17  for determining the height of the upper surface of the workpiece  14  and thus the thickness of the workpiece  14 . The sensor  18  is a position sensor  18  for determining the position of the workpiece  14  on the pallet  13 . The height sensor  17  and the position sensor  18  have each inductive proximity switches  19 ,  20 . In addition, an actuator  21 , which is used to affect the workpiece  14 , is schematically shown in the figure on the side of the pallet  13  facing away from the bench  12 . The actuator  21  may be, for example, a heater for heating the workpiece  14  or a bracing device for applying a clamping force on the workpiece  14 .  
         [0023]     As can be determined from  FIG. 1 , two transmission heads  22 ,  23  are arranged facing each other between the base  11  and the bench  12  in the area of the pivot axis A. The transmission head  22  is connected with a line  24  and a line  25 . Only a line  24  and a line  25  are shown here for the sake of greater clarity. However, at least one feed line and a return line are usually provided here instead of the line  24 , and likewise at least one feed line and a return line are provided instead of the line  25 . The line  24  is used to supply the components arranged on the pallet  13  with energy and is connected at its other end to a d.c. voltage source, not shown in the figure. The line  25  is used to send and receive information and is connected at its end facing away from the transmission head  22  to a modulator/demodulator unit, not shown in the figure. The transmission head  23  is connected to a transmission head  28  via two lines  26 ,  27  corresponding to the lines  24 ,  25 . The transmission head  28  faces a transmission head  29 , which is arranged on the side of the pallet  13  facing away from the workpiece  14 . The transmission head  29  is connected with a modulator/demodulator unit  32  by means of lines  30 ,  31 . The modulator/demodulator unit  32  is connected with the proximity sensor  20  by means of the lines  33 ,  34  and with the pressure sensor  16  and with the proximity sensor  19  by means of the lines  35 ,  36 . In addition, the modulator/demodulator unit  32  is connected with the actuator  21  by means of the lines  35 ,  36  and with the temperature sensor  15  by means of the line  36 .  
         [0024]      FIG. 2  schematically shows the design of the transmission head  22 . As can be determined from the figure, the transmission head  22  has a core  37 , on which a coil  38  and a coil  39 ,  40  are wound. The coil  38  is wound in the sink between the edges of the toroidal core  37  and is connected with the lines  24 . With an outer winding  39  connected with a line  25 , the coil  39 ,  40  leads at first around the toroidal core  37 , then changes over to the inner side of the toroidal core  37  and leads with an inner winding  40  back again in the opposite direction. The winding  40  is connected with the winding  39  at one end and with a line  25  at the other end.  
         [0025]      FIG. 3  shows a section through an edge area of the transmission head  22  and an edge area of the transmission head  23  associated with same. The design of the transmission head  23  corresponds to that of the transmission head  22  and has a toroidal core  41 , a coil  42  and a coil  43 ,  44  with an outer winding  43  and with an inner winding  44 . As can be determined from  FIG. 3 , the fields of the coils  38 ,  42  and of the coils  39  and  43  as well as  40  and  44  are extensively separated from one another in the manner described. The magnetic field  45  generated by the coil  38  encloses the coil  42  and induces a desired voltage there for the energy supply. The figure shows a snapshot of a state of the particular alternating currents through the coils  38 ,  42  and  39 ,  43  and  40 ,  44 . The magnetic field  46  generated by the outer winding  39  encloses the outer winding  43 . The magnetic field  47  generated by the inner winding  40  in the direction opposite the direction of the magnetic field  46  encloses, in contrast, the inner winding  44 . The fields  46 ,  47  for the information transmission can thus be extensively separated from the field  45  used for the energy transmission.  
         [0026]      FIG. 4  shows a block diagram of the device for the energy supply and for the information transmission with the features of the present invention. Identical elements are designated by the same reference numbers as in  FIGS. 1 through 3 . As can be determined from  FIG. 4 , an a.c. voltage source  48  is connected with the coil  38  of the transmission head  22  by means of two lines  24 . A coil  42  of the transmission head  23  is associated with the coil  38  and connected with the coil  49  of the transmission head  28  by means of the lines  26 . A coil  50  of the transmission head  29 , which is in turn connected with a prior-art rectifier circuit  51 , is associated with the coil  49 . The rectifier circuit  51  may be, for example, a prior-art rectifier circuit by means of diodes and is in turn connected with a voltage transformer  53  by means of lines  52 . A DC-DC voltage transformer  53  is provided as the voltage transformer in the exemplary embodiment being shown. The DC-DC voltage transformer  53  is connected with the sensors  15 ,  16 ,  17 ,  18  and the actuator  21 , which are not shown in the figure, by means of the lines  33 ,  35 .  
         [0027]     A control  54  is connected with an output of the DC-DC voltage transformer  53  by means of a line  55  and it is connected with the rectifier circuit  51  by means of another line  56  via the line  52 . In addition, the control  54  is connected with the sensors  15 ,  16 ,  17 ,  18  and with the actuator  21  by means of the lines  34 ,  36 . The control  54  is connected with a modulator/demodulator  58  by means of a plurality of lines  57 , of which only one line  57  is shown in the figure as a representative of these lines. The control  54  and the modulator/demodulator  58  together form the modulator/demodulator unit  32 .  
         [0028]     The modulator/demodulator  58  is connected by means of two lines  31  with a coil  59  of the transmission head  29 , which said coil  59  cooperates with a coil  60  of the transmission head  28 , which said coil  60  is associated with it [said coil  59 ]. The coil  60  of the transmission head  28  is connected with the coil  43 ,  44  of the transmission head  23  by means of the lines  27 . Associated with the coil  43 ,  44 , the coil  39 ,  40  of the transmission head  22  is associated with a modulator/demodulator  61  by means of the lines  25 . The modulator/demodulator  61  is connected with a control  63  by means of a plurality of lines  62 , of which only a line  62  is shown in the figure for the sake of greater clarity. The modulator/demodulator  61  and the control  63  together form a modulator/demodulator unit  64 . The control  63  is connected with the a.c. voltage source  48  by means of a line  65  and with a central control, which is not shown in the figure, by means of a line  66 . Even though the modulator/demodulator units  32 ,  64  are always shown separated from the transmission heads  22 ,  29  in the figures, the circuits necessary herefor may also already be integrated in the transmission heads  22 ,  29 .  
         [0029]     The mode of action of the energy and information transmission device of the rotary table  10  will be explained in greater detail below on the basis of  FIGS. 1 through 4 . The components arranged on the pallet  13  are supplied with energy by means of the coils  38 ,  42  and  49 ,  50  of the transmission heads  22 ,  23 ,  28 ,  29 . The coil  38  is supplied with an alternating voltage for this purpose from the a.c. voltage source  48  via the lines  24 . The alternating current thus flowing through the coil  38  generates a magnetic field, which is inductively coupled with the coil  42 . The alternating current generated inductively in the coil  42  of the transmission head  23  is sent by means of the lines  26  to the coil  49  of the transmission head  28 , where it in turn generates an alternating electromagnetic field, which is coupled inductively with the coil  50  of the transmission head  29 . The alternating current generated inductively in the coil  50  is sent via the lines  30  to the rectifier circuit  51 .  
         [0030]     The d.c. voltage rectified by the rectifier circuit  51  and, if necessary, smoothed with the use of means not shown in  FIG. 4 , is sent via the lines  52  to the DC-DC d.c. voltage transformer  53 , which transforms this d.c. voltage into a d.c. voltage with the desired voltage value and sends it to the components on the pallet  13  via the lines  33 ,  35 . At the same time, the DC-DC voltage transformer  53  also supplies the control  54  with the necessary operating voltage via the line  55 . The modulator/demodulator  58  is supplied, for example, via one of the lines  57 .  
         [0031]     The control  54  additionally receives the voltage rectified by the rectifier circuit  51  via the line  56 . The control determines from the value of this rectified voltage the state of the coupling of the coil  49  with the coil  50  and of the coupling of the coil  38  with the coil  42 . A controlled variable is thus generated for the a.c. voltage source  48 . Together with the sensor data, which the control  54  receives via the lines  34 ,  36 , this controlled variable is transmitted via the lines  57  to the modulator/demodulator  58  and digitally coded by same. The values to be transmitted are coded binarily in frequencies for this purpose, and the assignment of the frequencies to the values zero and one is selectable at the modulator/demodulator  58 , for example, by means of jumpers. The sensor data thus converted into a frequency signal and the controlled variable are sent to the coil  59  via the lines  31 . The coil  59  generates from this a.c. voltage sent to it an electromagnetic field, which is coupled with the coil  60  of the transmission head  28 . The voltage generated inductively in the coil  60  is in turn sent via the lines  27  to the coil  43 ,  44 , where an electromagnetic field is generated. The electromagnetic field generated by the coil  43 ,  44  is inductively coupled with the coil  39 ,  40 , where a corresponding voltage is induced and sent to the modulator/demodulator  61  by means of the lines  25 .  
         [0032]     The modulator/demodulator  61  has suitable filters in order to separate interfering signals from the useful signals. The signal thus filtered is first converted into so-called logic levels by means of a no-voltage compensation. For example, a comparison is performed for this purpose with a defined reference voltage in a comparator not shown in the figure. The signal thus processed is compared with a reference frequency by means of logical units, for example, so-called flip-flops. Distinction is made by comparison with this reference frequency whether the particular frequency signals received correspond to a zero or a one in a binary representation. The binary signal obtained is sent to the control  63  via the line  62  and evaluated there. The controlled variable determined by the control  54  by evaluating the voltage of the rectifier circuit  51 , which voltage is received via the line  56 , is converted into a corresponding control signal and sent via the line  65  to the a.c. voltage source  48 , which will then perform the corresponding adjustment of the a.c. voltage sent to the coil  28  via the lines  24 . This adjustment may consist, for example, of a change in the frequency of the a.c. voltage, the phase or the amplitude. The control  63  can also determine the current consumption or the power consumption of the a.c. voltage source  48  by means of one of the lines  65  and perform the adjustment depending on the result of this determination. The sensor signals obtained from the sensors  15 ,  16 ,  17 ,  18  by means of the lines  34 ,  36  are passed on by the control  63  via the line  66  to a central control, which controls the corresponding machining operations depending on these sensor signals.  
         [0033]     In addition, control signals are transmitted via the line  66  to the control  63  to control the actuator  21 . The control  63  controls via the line  62  the modulator/demodulator  61  for generating the voltage frequency-coded corresponding to the signals received to apply this alternating voltage to the coil  39 ,  40  via the lines  25 . The signal is then transmitted inductively from the coil  39 ,  40  to the coil  43 ,  44  and from there to the coil  60  via the lines  27 . A voltage corresponding to the signals is induced in the coil  59  by means of inductive coupling and passed on via the lines  31  to the modulator/demodulator  58 . A logical level is generated there similarly to the way it happens in the modulator/demodulator  61  by means of a zero voltage compensation, the frequency signals thus generated are compared with a reference frequency and, depending on the result of the comparison with the reference frequency, a binary code is generated from the values zero and one corresponding to the result of the comparison. This binary code is sent via the lines  57  to the control  54 , where the actuator  21  is actuated via the line  36  corresponding to the signals received.  
         [0034]     Bidirectional signal transmission from the base  11  to the pallet  13  and vice versa is thus possible by means of inductive coupling via the transmission heads  22 ,  23  and  28 ,  29 , and the energy needed on the pallet  13  is likewise transmitted to the pallet  13  via the transmission heads  22 ,  23  and  28 ,  29 . Since the transmission heads  22 ,  23  and  28 ,  29  use the same air gap for the transmission of the energy and the information, the monitoring of the voltage arriving at the pallet  13  is informative of the state of the particular air gaps, so that control of the voltage source  48  makes possible the constant energy supply of the components on the pallet  13 . At the same time, parasitic inductions can be compensated by monitoring the controlled variable.  
         [0035]      FIG. 5  shows another exemplary embodiment of a rotary table  67  having the features of the present invention. Identical elements are designated by identical reference numbers. As can be determined from the figure, the rotary table  67  has transmission heads  68 ,  69  instead of the transmission heads  22 ,  23 . The mode of action of the transmission heads  68 ,  69  corresponds to that of the transmission heads  22 ,  23 , but the transmission heads  68 ,  69  are coupled with one another radially rather than axially as are the transmission heads  22 ,  23 .  
         [0036]     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.