Abstract:
A three-in-one AC servo drive includes a main console, a control module, a power module and a plurality of servo motors. A single drive can be connected to a plurality of motors. The power module and control module for the motors can be integrated to a single modular unit. Therefore, the redundant portion such as communication interface, display unit and I/O unit can be eliminated. The capacitor of the bus of the IGBT module can also be reduced, whereby the occupied space and cost can be reduced with less assembling time.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an AC servo drive, especially to a three-in-one AC servo drive. 
   2. Description of Prior Art 
   The current multi-axes control system is a centralized system with a main console. The main console controls servo drive to control linear/circular interpolation movement of servo motors through conventional wiring or high speed communication. 
   The AC servo motor is generally used for machine with more than three axes or multi-axes system. The AC servo motor is designed to have a servo drive connected to a motor, or a servo drive connected to a plurality of motors in a one-to-many design. The later is an expandable modularized design wherein the power units for the motors are expanded when more motors are to be connected. However, the wiring and assembling time do not gain advantage in efficiency and cost down. 
   SUMMARY OF THE INVENTION 
   The present invention is to provide a three-in-one AC servo drive, where on drive is connected to a plurality of motors and the power modules and control modules for the motors are integrated in the same module. The redundant portions such as communication interfaces, display units, I/O units, capacitors of IGBT module of the power module can be saved, whereby the occupied space and cost can be reduced with less assembling time. 
   Accordingly, the present invention provides a three-in-one AC servo drive comprising a main console, a control module, a power module and a plurality of servo motors. The control module comprises: 
   a communication interface transmitting bi-directional command and data with the main console; 
   an I/O unit transmitting bi-directional analog/digital I/O signals; 
   a current detector used to receive current signals corresponding servo motors and converting the current signals to digital current signals; 
   an FPGA used to detect rotational position and rotational speed of the servo motors and outputting digital signals of rotational position and rotational speed, the FPGA generating PWM signals corresponding to current of servo motors; 
   a digital signal processor (DSP) receiving speed command, position command and torque command from the main console through the communication interface, receiving the analog/digital I/O signals from the I/O unit, receiving the digital current signal from the current detector and receiving the digital signals of rotational position and digital signals of rotational speed from the FPGA, the digital signal processor (DSP) obtaining a PWM signal for current of the servo motor based on those signals, the digital signal processor (DSP) outputting the PWM signal to the FPGA and sending operation status of the servo motor to the main console; and 
   the power module comprising: 
   a converter to convert AC power to DC power; 
   a power bus providing DC power to the converter; 
   a capacitor for stabilizing DC power for the power bus; 
   a plurality of inverters converting DC power of the power bus to AC power and generating AC voltage and AC current for corresponding servo motor according to PWM signal of the FPGA; and 
   a plurality of current sensors for sensing current supplied from the inverter to the servo motors and outputting sensed current signal to the current detector. 

   
     BRIEF DESCRIPTION OF DRAWING 
     The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself however may be best understood by reference to the following detailed description of the invention, which describes certain exemplary embodiments of the invention, taken in conjunction with the accompanying drawings in which: 
       FIG. 1  shows the block diagram of the three-in-one AC servo drive according to the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows the block diagram of the three-in-one AC servo drive according to the present invention. The three-in-one AC servo drive  10  comprises a main console  12 , a control module  14 , a power module  16  and a plurality of servo motors  18 . 
   The main console  12  comprises a communication interface  20 , an I/O unit  22 , a current detector  24 , a field programmable gate array (FPGA)  26 , a digital signal processor (DSP)  28  and a display unit  30 . The FPGA  26  comprises a position/speed detector  32  and a phase width modulation (PWM) controller  34 . 
   The power module  16  comprises a converter  36 , a power bus  38 , a capacitor  40 , a braking unit  42 , a plurality of inverters  44  and a plurality of current sensors  46 . 
   The communication interface  20  and the main console  12  transmit command and data bi-directionally. For example, the main console  12  sends speed command, position command and torque command to the communication interface  20 . The communication interface  20  sends the operation status of the servo motors  18  output from the digital signal processor (DSP)  28 . The communication interface  20  comprises RS-485, an RS232, an Modbus and a CAN-open. 
   The I/O unit  22  and the main console  12  transmit digital/analog I/O signals bi-directionally. The I/O unit  22  has analog to digital conversion function or digital to analog conversion function, and digital input/output (DI/DO) function. 
   The current detector  24  receives a plurality of current signals corresponding to the servo motors  18  and converts the current signals to digital current signals for outputting to the digital signal processor (DSP)  28 . The current sensor  46  senses the current supplied from the inverter  44  to the servo motor and sends the sensed current to the current detector  24 . 
   The position/speed detector  32  of the FPGA  26  detects the rotational position and speed of the servo motors  18 , and then sends digital signals of rotational position and digital signals of speed to the digital signal processor (DSP)  28 . The phase width modulation (PWM) controller  34  of the FPGA  26  generates PWM signals corresponding to the current of the servo motor  18  according to the PWM signal of the digital signal processor (DSP)  28 . 
   The digital signal processor (DSP)  28  receives speed command, position command and torque command from the main console  12  through the communication interface  20 , receives the analog/digital I/O signals from the I/O unit  22 , receives the digital current signal from the current detector  24  and receives the digital signals of rotational position and digital signals of rotational speed from the position/speed detector  32  of the FPGA  26 . The digital signal processor (DSP)  28  obtains a PWM digital signal for current of the servo motor  18  based on those signal and high speed calculation thereof. The digital signal processor (DSP)  28  outputs the PWM digital signal to the phase width modulation (PWM) controller  34  of the FPGA  26 . The digital signal processor (DSP)  28  sends the operation status of the servo motor  18  to the main console  12  through the communication interface  20 . 
   The display unit  30  receives data from the digital signal processor (DSP)  28  and displays the voltage, current, position, speed and error message for each of the servo motors  19 , wherein the display unit  30  can be a seven-segment display. 
   The converter  36  converts the three-phase power  48  into DC power. The power bus  38  provides DC power to the converter  36 . The capacitor  40  is used to stabilize the DC power of the power bus  38  by reducing ripples of the power bus  38 . The converter  36  can be bridge rectifier to convert the three-phase AC power  48  to DC power. 
   The inverter  44  converts the DC power of the power bus  38  into AC power and generates AC voltage and currents corresponding to the servo motors  18  according to the PWM signal from the phase width modulation (PWM) controller  34  of the FPGA  26 . The inverter  44  is a full-bridge three-phase converter and converts DC power of the power bus  38  to three-phase AC voltage and current with varied frequency and varied amplitude. A six-bridge converter  44  with IGBT (Insulated Gate Bipolar Transistor) module uses a six-bridge switch to convert the DC power of the power bus to desired varied frequency and varied amplitude, where large DC voltage and current are converted to AC voltage and current. As can be seen in  FIG. 1 , the three sets of six-bridge converter  44  for the three-axes servo motors  18  uses the same DC voltage source. The six-bridge converter  44  releases the braking unit for the power bus  38  when the voltage of the power bus  38  is excessive. Therefore, the power module  16  can eliminate common portion in comparison with original one-by-one drive. 
   As can be seen from above description, the redundant elements such as braking unit  42 , capacitor  40  and converter  36  can be eliminated by using voltage of common converter  36 , power bus  38  and capacitor  36 . The size of heat-dissipating plate (not shown) can also be reduced. The redundant elements such as display unit  30 , communication interface  20  and I/O units  22  for the control module  14  can also be reduced. The hi-speed digital signal processor (DSP)  28  is more cost-effective then three DSPs. This will be more completive in cost in comparison with multi-axes system such as three-axes systems. 
   The present invention has the advantage of using one drive to connect a plurality of motors and the power modules of the motors can be placed in the same module. The motors can use the common drive portion such as communication interface, display unit, I/O units. The capacitor of the IGBT module of the power module can be reduced. The size will be more compact, the cost, wiring and assembling time can also be reduced. 
   Although the present invention has been described with reference to the preferred embodiment thereof, it will be understood that the invention is not limited to the details thereof. Various substitutions and modifications have suggested in the foregoing description, and other will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.