Abstract:
A robot control system including a servo amplifier supplying power to a robot, a processor controlling the operation of the robot, and a servo power connection/cutoff circuit connected to the same, issuing excitation/nonexcitation commands to a charging relay and a main circuit connection electromagnetic contactor provided in the circuit from the processor, monitoring the opened/closed states of the contacts of the charging relay and main circuit connection electromagnetic contactor by the processor, and detecting if their contacts open and close as instructed by the processor to thereby check if the power connection/cutoff circuit has a fault. Due to this, it is possible to provide a robot control system which detects faults of the power connection/cutoff circuit and which is inexpensive and high in safety.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a robot control system and, more particularly, relates to a robot control system having an inexpensive, high safety servo power connection/cutoff circuit utilizing software. 
   2. Description of the Related Art 
   A servo amplifier of a robot control system is provided with an AC/DC converter. In such a servo amplifier, when the power is turned on, a large rush current would flow through a smoothing capacitor in the servo amplifier (hereinafter simply referred to as a “capacitor”), so the robot control system is provided with a precharging circuit. 
   At the time of startup of the servo amplifier, to enable a charging resistance in the precharging circuit (hereinafter simply referred to as the “resistance”) and a serial contact (relay or solenoid switch) to perform the precharging at the time of startup, then connect to the main power source, a main circuit contact is provided parallel to the serial line between the resistance and serial contact, the contact in series with the resistance is closed to start the precharging, the capacitor is charged, then the main circuit contact is closed. 
   On the other hand, when cutting the servo power at the time of an emergency stop, both the precharging contact and the main circuit contact are opened, but for safety&#39;s sake, it is necessary to detect faults such as melt fusion of the contacts. 
   In the related art, for example, in the emergency stop circuit described in Japanese Patent Publication (A) No. 2004-237416 (see specification, paragraph nos. [0023] to [0037] and drawings, FIGS. 3 and 4) or Japanese Patent Publication (A) No. 2005-165755 (see claims, [Claim 1], specification, paragraph nos. [0023] to [0037], and drawings, FIGS. 1 and 2), the function of detecting melt fusion faults of contacts was realized by using hardware circuits, but the circuits were complicated and the costs high. 
     FIG. 1  is a general electrical system diagram of the robot  1  and the robot control system  2 . The controller  11  shown in  FIG. 1  includes a CPU for controlling the robot operation and its peripheral circuits and enables the robot  1  to perform predetermined work by issuing commands to the servo amplifier  12  to control the robot  1  in operation and posture. 
   Further, the controller  11  has a teaching pendant  13  connected to it. The teaching pendant  13  is operated by a worker to teach the robot  1  an operation or to input various settings into the robot control system  2 . 
   The servo amplifier  12  drives a servo motor attached to each joint of the robot  1  based on a command from the controller  11 . Further, the servo amplifier  12  receives feedback information relating to the rotational angle and speed from a rotary encoder attached to each servo motor through a signal line  15  and transmits information necessary for control of these servo motors to the controller  11 . 
   The servo power connection/cutoff circuit  14  turns on the drive power for the servo motors of the robot  1  through the servo amplifier  12  and power line  16  in accordance with a request for startup of the robot  1  or immediately cuts the supply of drive power to the servo motors to ensure safety when there is a request for emergency stop. 
     FIG. 2  is a block diagram of the configuration of the servo amplifier  12  shown in  FIG. 1 . The servo amplifier  12  has an AC/DC converter  21  for converting a drive power, that is, an AC power, to a DC power and an inverter  22  for converting a DC power to an AC power controlled in current by a command from the controller  11 . Further, to smooth the output voltage of the AC/DC converter  21 , a large capacity smoothing capacitor  23  is provided. The inverter  22  receives as input the DC voltage smoothed by the capacitor  23 . 
   When connecting the servo power to the servo amplifier  12 , if directly applying the power voltage in the state with the capacitor  23  insufficiently charged, a large rush current would flow into the capacitor  23  and the electrical circuits in the current path would be adversely affected or a temporary voltage drop would be caused, so before connecting the power source, the general practice has been to precharge the capacitor  23  through a resistance. 
     FIG. 3  is a view of details of the servo power connection/cutoff circuit  14  shown in  FIG. 1 , while  FIG. 4  is a view showing the change in state of the servo power connection/cutoff circuit  14  shown in  FIG. 3 . The servo power connection/cutoff circuit  14  shown in  FIG. 3  has the function of cutting the supply of drive power to the servo amplifier  12  (hereinafter referred to as the “servo power”) when the operator pushes the emergency stop switch  31  and the function of connecting the servo power when the operator releases the emergency stop switch  31  and pushes the reset switch  32 . 
   Further, when connecting the servo power, it has the function of precharging to prevent a large rush current from flowing to the servo amplifier  12 . 
   Below, details of the servo power connection/cutoff circuit  14  will be explained. In  FIG. 3  and  FIG. 4 , KA 1 , KA 2 , and KA 3  indicate relays, while KM 1  and KM 2  indicate electromagnetic contactors. The relays and electromagnetic contactors used are ones for which linkage between normally open contacts and normally closed contacts is ensured (interlocked). 
   For example, when the contact KM 1 - 1  of the KM 1  is closed, the normally open contacts KM 1 - 4  to KM 1 - 6  being in the open state is guaranteed. 
   First, these relays (KA 1  to KA 3 ) and electromagnetic contactors (KM 1 , KM 2 ) are all in the OFF state (state of S 0  of  FIG. 4 ). 
   At this time, if the relays and electromagnetic contactors are free of faults such as melt fusion or reset defects of the normally open contacts and the normally open contacts open, the contacts KA 2 - 2 , KM 1 - 1 , KA 3 - 2 , and M 2 - 1  become closed. 
   If the operator pushes the reset switch  32  in this state, the KA 1  enters the ON state and the KA 1 - 1  and KA 1 - 2  close (state of S 1  of  FIG. 4 ). At this time, if the emergency stop signal switch  31  is in the closed state, the KA 2  and KA 3  turn ON through these contacts (state of S 2  of  FIG. 4 ). Note that if the emergency stop switch  32  is in the opened state, KA 2  and KA 3  will never turn ON. 
   If the KA 2  and KA 3  turn ON, the KA 2 - 2  and KA 3 - 2  are opened, so the KA 1  enters the OFF state, but current flows through the KA 2 - 1  and KA 3 - 1 , so while the emergency stop switch  31  is in the closed state, the ON states of KA 2  and KA 3  are held (state of S 3  of  FIG. 4 ). Therefore, the operation of pushing the reset switch  32  may be short in time. 
   When the KA 2  becomes ON and the KA 1  becomes OFF, the KM 1 - 3  and the KM 2 - 3  become closed and the KM 1  is ON. At this time, the KM 1 - 4  to KM 1 - 6  and the KA 3 - 4  to KA 3 - 6  are in the closed state and the KA 3  is ON, so the capacitor  23  in the servo amplifier  12  is charged through the KA 3 - 4  to KA 3 - 6  and charging resistance  35 . The current at this time is limited by the charging resistance  35 , so a large rush current will not flow. 
   The power-up delay circuit  36  is set so as to turn ON the KM 2  through the KA 1 - 3  to KA 3 - 3  after the time for the capacitor  23  in the servo amplifier  12  to be sufficiently charged elapses from the time when the KA 3  turns ON. Due to this, the rush current is prevented from flowing when the KM 2 - 4  to KM 2 - 6  are ON. 
   In the above way, finally, only the KA 1  enters the OFF state while the other KA 2 , KA 3 , KM 1 , and KM 2  all become the ON state, whereby the preparations for operation end (state of S 4  of  FIG. 4 ). 
   When the button of the emergency stop switch  31  is pushed, all of the relays (KA 1  to KA 3 ) and electromagnetic contactors (KM 1 , KM 2 ) turn OFF and the initial state (state of S 0  of  FIG. 4 ) is returned to. 
   In the event that in the relays or electromagnetic contactors forming the servo power connection/delay circuit  14 , the normally open contacts melt fuse or other reasons occur in the initial state (S 0 ) and the normally open contacts can no longer be reset, the contacts corresponding to the faulty parts in the KA 2 - 2 , KM 1 - 1 , KA 3 - 2 , and M 2 - 1  will not become the closed state. Therefore, the change from S 0  to S 1  will not occur and the servo amplifier will not enter a state where it is supplied with power, that is, the state of S 3  and S 4  will not be reached. Therefore, the operator will notice the fault and servo power will not longer be supplied in the faulty state, so safety will be secured. 
   Due to the above power connection/cutoff circuit, safety against a fault in the power connection/cutoff circuit can be secured. Due to the precharging, the rush current to the servo amplifier can be suppressed. Due to the increased complexity of the circuit and the increase in the number of parts, an increase in cost cannot be avoided. Further, relays where linkage between the normally open and normally closed contacts is guaranteed are extremely expensive compared with general relays. This also is a factor to increase costs. 
   Before turning the servo power ON, it is possible to detect faults in the power connection/cutoff circuit, but once turning the power ON, there is the problem that a fault cannot be detected while ON. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a robot control system which detects faults of a power connection/cutoff circuit and which is inexpensive and high in safety. 
   To achieve the above object, there is provided a robot control system controlling a servo power connection/cutoff circuit by using a processor, having the processor issue connection/cutoff commands to a precharging relay and a main circuit connection electromagnetic contactor, and able to monitor the states of connection/cutoff from the processor, the robot control system having the processor detect if their contacts have opened/closed as instructed so as to detect if the servo power connection/cutoff circuit has a fault. 
   Specifically, there is provided a robot control system provided with a processor, a servo amplifier having an AC/DC converter, a resistance for preventing a rush current at the time of charging a smoothing capacitor in the AC/DC converter, a first contact connected in series to the resistance, a first switch circuit opening/closing the first contact by a command from the processor, a first detection circuit detecting an opened/closed state of the first contact and notifying it to the processor, a second contact provided in parallel to the resistance and first contact, a second switch circuit opening/closing the second contact by a command from the processor, and a second detection circuit detecting an opened/closed state of the second contact and notifying it to the processor, the robot control system operating so that when charging the capacitor, it closes the first contact to charge the capacitor, then closes the second contact, wherein the processor commands the first switch circuit and second switch circuit to open/close the first contact and second contact and wherein the first detection circuit and second detection circuit detect if the first contact and second contact open/close as instructed so as to check for abnormalities of the first contact and second contact. 
   According to the present invention, it becomes possible to provide a robot control system having an inexpensive, high safety servo power connection/cutoff circuit enabling deliberate opening/closing of the contact of the precharging relay and the contact of the main circuit electromagnetic contactor and a check of the operations of the precharging relay and the main circuit electromagnetic contactor even while the power of the servo amplifier is ON. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and features of the present invention will become clearer from the following description of the preferred embodiments given with reference to the attached drawings, wherein: 
       FIG. 1  is a general electrical system diagram of a robot and a robot control system; 
       FIG. 2  is a block diagram of the configuration in a servo amplifier shown in  FIG. 1 ; 
       FIG. 3  is a view showing details of the servo power connection/cutoff circuit shown in  FIG. 1 ; 
       FIG. 4  is a view showing the changes in state of the servo power connection/cutoff circuit shown in  FIG. 3 ; 
       FIG. 5  is a view of a first embodiment of a servo power connection/cutoff circuit according to present invention; 
       FIG. 6  is a time chart showing the sequence when turning on the servo power; 
       FIG. 7  is a time chart showing a first fault check method of a servo power connection/cutoff circuit after the servo power is turned on; 
       FIG. 8  is a time chart showing a second fault check method of a servo power connection/cutoff circuit after the servo power is turned on; and 
       FIG. 9  is a view showing a second embodiment of a servo power connection/cutoff circuit according to the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be described in detail below while referring to the attached drawings. 
     FIG. 5  is a view of a first embodiment of a servo power connection/cutoff circuit according to the present invention. As shown in  FIG. 5 , the servo power connection/cutoff circuit  50  is connected to a processor  51  and a servo amplifier  52 . An emergency stop switch, a reset switch, a contact KA 1 - 0  of a precharging relay KA 1 , and a contact KM 1 - 0  of a main circuit electromagnetic contactor KM 1  are connected to an input circuit  53 . The states of these switches and contacts can be read by the processor  51 . The capacitor in the servo amplifier  12  is charged through a contact KA 1 - 1  of the precharging relay KA 1  and charging resistance  55 . 
   Further, signal lines instructed from the processor  51  and output from an output circuit  54  are connected to a coil exciting the precharging relay KA 1  and a coil exciting the main contact electromagnetic contactor KM 1  and enable the processor  51  to control the opening/closing of the contacts of the precharging relay KA 1  and main contact electromagnetic contactor KM 1 . 
   First, the method of checking for a fault of the servo power connection/cutoff circuit  50  at the time of turning on the servo power will be explained using  FIG. 6 . 
     FIG. 6  is a time chart showing the sequence when turning on the servo power. First, when turning on the servo power, the precharging relay KA 1  and the electromagnetic contactor KM 1  all are OFF. At this time, if the normally open contact KA 1 - 1  of the relay KA 1  and the normally open contact KM 1 - 1  of the electromagnetic contactor KM 1  are free from faults such as melt fusion or reset defects and the normally open contacts KA 1 - 1  and KM 1 - 1  open, the normally closed contact KA 1 - 0  of the relay KA 1  and the normally closed contact KM 1 - 0  of the electromagnetic contactor KM 1  become the closed state. The states of these normally closed contacts KA 1 - 0  and KM 1 - 0  can be read from the processor  51  through the precharging relay monitor input and main contact monitor input in the input circuit  53 , so the processor  51  can judge that the precharging relay KA 1  and electromagnetic contactor KM 1  are free from faults. 
   If the operator pushes the reset switch in this state, the processor  51  detects that the reset switch has been pushed through the input circuit  53 . At this time, only when the fact that the emergency stop signal switch is in the closed state and both the precharging relay monitor input and main contact monitor input are ON, that is, are in the closed contact states can be read through the input circuit  53 , the processor  51  issues an ON command to the precharging relay KA 1  (timing of t 1 ). 
   The processor  51  turns ON the precharging relay KA 1 , then after a certain time or after detecting that the capacitor in the servo amplifier  52  is sufficiently charged, issues an ON command to the main circuit electromagnetic contact KM 1  (timing of t 2 ). 
   After the timing of t 2 , the fact that the precharging relay monitor input and main contact monitor input are both in the OFF state is read by the processor  51 , wherein the fact that the input circuit  53  is free from a fault is confirmed. 
   Next, the method for checking for a fault in the servo power connection/cutoff circuit  50  after turning on the servo power will be explained using  FIG. 7 . 
     FIG. 7  is a time chart showing a first fault check method of the servo power connection/cutoff circuit after turning on the servo power. After turning on the servo power, the precharging relay KA 1  and electromagnetic contactor KM 1  are both in the ON state. In this state, the processor  51  issues them OFF commands (timing of t 3 ). At this time, if the relay KA 1  and the electromagnetic contactor KM 1  are free from faults such as melt fusion or reset defects of the normally open contacts KA 1 - 1  and KM 1 - 1  and the normally open contacts KA 1 - 1  and KM 1 - 1  open, the normally closed contacts KA 1 - 0  and KM 1 - 0  of the relay KA 1  and electromagnetic contactor KM 1  become the closed states. The states of the normally closed contacts KA 1 - 0  and KM 1 - 0  can be read through the precharging relay monitor input and main contact monitor input from the processor  51 , so the processor  51  confirms that the precharging relay KA 1  and electromagnetic contactor KM 1  are free from faults. 
   After this, immediately, the precharging relay KA 1  and electromagnetic contactor KM 1  are issued ON commands, and the precharging relay KA 1  and electromagnetic contactor KM 1  return to the ON states (timing of t 4 ). While the precharging relay KA 1  and electromagnetic contactor KM 1  are OFF, the servo amplifier  52  is not supplied with power, but this is an extremely short time of tens of milliseconds. During this time, by continuing the operation by the charged power of the capacitor in the servo amplifier  52 , the effect on the robot operation can be almost completely ignored. 
   This fault check can be performed by a command from the processor  51 , so can be performed while avoiding times of operations where the power consumption is large and suspension of the supply of power would be liable to have a detrimental effect. As examples, the fault check can be performed in a state braking the shafts of the robot and stopping the supply of torque to the servo motors, can be performed in a state while the robot is idle between one job and another etc. 
     FIG. 8  is a time chart showing a second fault check method of a servo power connection/cutoff circuit after turning on the servo power. In the examples above, the precharging relay KA 1  and the electromagnetic contactor KM 1  were simultaneously checked for faults, but it is also possible to separate the timings for fault checks of the precharging relay KA 1  and electromagnetic contactor KM 1  and thereby enable fault checks without completely stopping the supply of power to the servo amplifier  52 . This example will be explained below with reference to  FIG. 8 . 
   After turning on the servo power, the precharging relay KA 1  and electromagnetic contactor KM 1  are both in the ON state. In this state, the processor  51  issues an OFF command to the first precharging relay KA 1  (timing of timing of t 5 ). At this time, if the precharging relay KA 1  is free from any fault such as melt fusion or reset defects of the normally open contact KA 1 - 1  and the normally open contact KA 1 - 1  opens, the normally closed contact KA 1 - 0  of the precharging relay KA 1  becomes the closed state. The state of the normally closed contact KA 1 - 0  of the precharging relay KA 1  can be read from the processor  41  through the precharging relay monitor input, so the processor  51  confirms that the precharging relay KA 1  has no fault. The processor  51  then immediately issues an ON command to the precharging relay KA 1 , whereby the precharging relay KA 1  and electromagnetic contactor KM 1  return to the ON state (timing of t 6 ). 
   The processor  51  next issues an OFF command to the electromagnetic contactor KM 1  (timing of t 7 ). At this time, if the electromagnetic contactor KM 1  is free from a fault such as melt fusion or reset defects of the normally open contact KM 1 - 1  and the normally open contact KM 1 - 1  opens, the normally closed contact KM 1 - 0  of the electromagnetic contactor KM 1  becomes the closed state. The state of the normally closed contact KM 1 - 0  of the electromagnetic contactor KM 1  can be read by the processor  51  through the main contact monitor input, so the processor  51  confirms that the electromagnetic contactor KM 1  is free from any fault. After this, it immediately issues an ON command to the electromagnetic contactor KM 1 , whereby the electromagnetic contactor KM 1  returns to the ON state (timing of t 8 ). 
   In accordance with this timing, when the precharging relay KA 1  turns OFF, power is supplied to the servo amplifier  52  through the main circuit electromagnetic contactor KM 1 . Further, when the main circuit electromagnetic contact KM 1  is OFF, power is supplied to the servo amplifier  52  through the precharging relay KA 1 , so it is possible to suppress to a minimum the effects of the fault check on the robot operation. Here, first the precharging relay KA 1  is checked, then the electromagnetic contactor KM 1  is checked, but the reverse order also gives exactly the same effect. 
   Note that, to facilitate understanding, in the first embodiment, the case of a single electromagnetic contactor was explained, but like with the circuit explained with reference to the related art, the present invention can also be worked in a circuit with two electromagnetic contactors. 
     FIG. 9  is a view of a second embodiment of a servo power connection/cutoff circuit according to the present invention. The second embodiment differs from the first embodiment shown in  FIG. 5  in the point of provision of two electromagnetic contactors. In the servo power connection/cutoff circuit  90  of this second embodiment, in addition to the servo power connection/cutoff circuit  50  shown in  FIG. 5 , the second electromagnetic contactor KM 2  is provided and control is performed from a second processor  91 A separated from the first processor  91 . The emergency stop switch used is a double contact one having a first contact and a second contact. 
   The first contact of the emergency stop switch, the reset switch, the contact KA 1 - 0  of the precharging relay KA 1 , and the contact KM 1 - 0  of the main circuit electromagnetic contactor KM 1  are connected to the input circuit  93  and enable the states of these switches and contacts to be read from the processor  91 . The capacitor in the servo amplifier  12  is charged through the contact KA 1 - 1  of the precharging relay KA 1  and charging resistance  95 . 
   Further, signal lines instructed from the processor  91  and output from the output circuit  94  are connected to the coil exciting the precharging relay KA 1  and the coil exciting the main contact electromagnetic contactor KM 1  and enable control of the opened/closed states of the contacts of the precharging relay KA 1  and main contact electromagnetic contactor KM 1  from the processor  91 . 
   The control by the second processor  91 A is performed so that a fault in any one processor among the first processor  91  and the second processor  91 A will not cause a loss of the emergency stop or other safety functions and is a general technique. In this case as well, these processors  91  and  91 A can perform the check based on the present invention. 
   The second contact of the emergency stop switch and the contact KM 2 - 0  of the main circuit electromagnetic contactor KM 2  are connected to the input circuit  93 A and enable the states of these switch and contact to be read from the processor  91 A. 
   Further, the signal line instructed from the processor  91 A and output from the output circuit  94 A is connected to the coil exciting the main contact electromagnetic contactor KM 2  and enables control of the open/closed state of the contact of the electromagnetic contactor KM 2  from the processor  94 A. 
   Further, to secure safety and minimize the effect of the fault check on the robot operation, it is also possible to check only the KA 1  and KM 1  by the fault check shown in  FIG. 8  after turning on the servo power and not check the KM 2  by the fault check after turning on the servo power source. 
   While the invention has been described with reference to specific embodiments chosen for purpose of illustration, it should be apparent that numerous modifications could be made thereto, by those skilled in the art, without departing from the basic concept and scope of the invention.