ARTICULATED ROBOT

Abstract: An articulated robot comprises one or more articulation angles that can assume two states on the occasion of the same position or attitude of an object being controlled. A change from one to the other of the above described two states is taught by operating an operation panel and the respective driving means of two arms constituting one articulation angle are controlled based on the above de­ scribed teaching information so that the articulation angle may be changed from one state to the other state, whereby rotation of the respective arms is controlled.

Description: Background of the invention Field of the invention The present invention relates to an articulated robot. More particularly, the present invention relates to a robot having the features of the preamble of claim 1. These robots can be advantageously utilized in an automatic welding apparatus or the like. Description of the prior art Articulated robots have been heretofore utilized in manipulators or other types of automated machines. An example of such an articulated robot is disclosed in JP-A-50.000376. A typical articulated robot comprises at least a first arm mounted rotatably at one end about a fixed shaft, and a second arm mounted rotatably about the free end of the above described arm. A third arm, a fourth arm and so on may be turnably provided in succession and a functional element such as a welding torch, a gripper or the like may be provided at the free end of the last arm. The turning angles between adjacent arms are individually controlled so as to position the functional element at the free end to perform the desired task. In US-A-4,163,183 there is disclosed a programmable automatic assembly system which includes co-operating manipulator arms programmable to assemble parts on a centrally located work table. Facilities are provided for teaching the manipulator arms and these include a closed loop facility for maintaining the arm in a previously taught position during the teaching of the present position. A computer assists in the teaching operation performing a number of tasks which would be otherwise extremely difficult for the human operator. A conventional articulated robot arm, such as the above, is adapted such that the first arm and the second arm turnably provided on the first arm may, starting from a state in which both arms are in alignment, assume a state in which the first arm and the second arm are angled in relation to each other about their common rotation shaft. However it can easily be shown that a single point of space may be reached by the free end of the articulated robot with the two arms in either one of two relative attitudes. A conventional articulated robot arm is usually adapted such that a point in space may be controllably achieved in one of the relative attitudes only. However, if the control is such that the arms can assume only one relative attitude, it is possible that the free end of the arm could collide with the workpiece depending on the geometry of the workpiece. In such a case, a welding torch, for example, cannot be controlled sufficiently to reach the target position, unless the workpiece's fixing position or attitude is changed during the welding operation. This will increase operation execution time. In "Bulletin of the JSME", vol. 22, No. 173, November 1979, pages 1640 to 1647, it is proposed to operate a robot in a selected one of a number of different coordinate systems, including cylindrical coordinate systems to avoid the singular points and an "arm coordinate system to change the kind of the configuration of the arm", depending on the task being performed. However, orthogonal coordinate systems have advantages, including ease of use by an operator and facilitation of interpolation operations, which would be lost by switching to a different coordinate system. SUMMARY OF THE INVENTION To overcome this difficulty, according to the invention there is provided an articulated robot comprising an arm assembly including a pair of mutually articulated arms capable of supporting an object, drive means for driving the arm assembly to shift the object, and control means for controlling said drive means, said control means including teaching means whereby orthogonal coordinate data defining a position or attitude of the object can be produced and stored by the control means to allow the control means to control the drive means in such a manner as to cause the arm assembly to shift the object to that position or attitude, said arm assembly being able to assume at least two different states of bending for a position or attitude of the object defined by said orthogonal coordinate data, the articulation angle between the arms being different in the respective states, characterised in that: said teaching means includes means for enabling selection between the different bending states of the arm assembly and said control means include storage means for enabling the control means to store state indication data forming an indication of which of the states has been selected, in addition to said orthogonal coordinate data, when said teaching means is operated to enable teaching of a point, said control means being operable, when the robot is to move the object to a defined position or attitude, to instruct a desired inversion of the bending state of the arm assembly if, and only if, the stored state indication data for a present taught point differs from the stored state indication data for the previous taught point and the arm assembly was within a predetermined critical zone for said previous taught point, said critical zone comprising bending states in which the two mutually articulated arms are aligned with one another or are displaced out of alignment by no more than a very small angle, whereby when it is desired that the robot should move the object from a first position or attitude, in which the arm assembly is in one bending state outside the critical zone, to a second position or attitude in which the arm assembly is in a different bending state, but also outside the critical zone, then it is necessary that the robot be taught an intermediate position or attitude for which the arm assembly would be within the said critical zone. With a conventional articulated robot, it could happen that a workpiece collides with such turnable arms depending on the shape of a workpiece or the position of a welding point, for example, which necessitated a change of the position of the workpiece to avoid such situation. However, according to the present invention, since the state of such turnable arms can be reversed, such possible collision can be eliminated without changing the position of the workpiece. Since such reversion of the state of the turnable arms can be simply taught and reproduced, manipulation of the machine is more facilitated. According to one embodiment of the present invention, information representing which one of the two states is taught. Accordingly, the respective driving systems control the corresponding arms responsive to the information representing such states. An articulated robot employing the present invention comprises a support member, a first arm having the base end thereof pivoted by a first shaft on the support member, a second arm having the base end pivoted by a second shaft in parallel with the first shaft at the tip end of the first arm, a first and second prime movers for controlling the turnable angle of the first and second arms provided rearward of the support member, the first prime mover and the first arm being coupled through a pulley and belt and the second prime mover and the second arm being coupled through a counter pulley coaxial with the first shaft, a pulley coaxial with the second shaft, and a belt set therebetween. According to the embodiment. a mechanism for controlling the arms is implemented not by a conventional parallelogram link mechanism but by a combination of belts and pulleys and therefore can drastically increase the range of the turnable angle of the respective arms as compared with a conventional one. Since a prime mover is provided rearward of the support member, there is little possibility of collision of the prime movers with an operator or a workpiece when the support member is to be turned. By coupling the pulleys at the last stage to the output shaft of speed reducing apparatus, a tension of the belts can be decreased as much as possible, whereby extension thereof can be decreased as much as possible. Therefore, accuracy which is liable to the influenced by such extension is much more improved. Brief description of the drawings Fig. 1 is a view showing an automatic welding apparatus by way of an example of an articulated robot which constitutes the background of the invention and in which the present invention can be employed; Fig. 2 is a block diagram showing an outline of one embodiment of the present invention; Figs. 3 to 5 are flow diagrams for explaining the operation of the embodiment; Fig. 6 is a view for explaining the state of a critical zone of the turnable arms; Figs. 7 to 14 are views for use in explaining coordinates conversion; Fig 15 is a perspective view of another example of the articulated robot in which the present invention can be employed; Fig. 16 is a perspective view of an internal structure of the Fig. 15 embodiment; and Figs. 17 to 21 are views showing in some detail those portions associated with the control of the respective axes of the Fig. 15 embodiment. Description of the preferred embodiments Fig. 1 is a view showing one example of an automatic welding apparatus employing an articulated robot which constitutes the background of the invention and in which the present invention can be employed. A fixing member 1 Is fixed to the ground, for example, and the fixing member 1 is provided with a cylindrical base 3 of a relatively small height. A cylindrical rotating member 4 of a relatively large height is provided to be rotatable about a rotation axis, not shown, on the top of the cylindrical base 3. A vertical rotating shaft is provided in a hollow portion, not shown, of the cylindrical rotating member 4 and a rotating member 5 is provided on the above described cylindrical rotating member 4 so as to be supported to be rotatable integrally with the cylindrical rotating member 4. The cylindrical rotating member 4 and thus the rotating member 5 is driven to be rotated for the rotation angle α₁ by means of a motor, not shown, to be described subsequently. The rotating member 5 has supporting members 7 extending from the top surface thereof In the vertical direction and in parallel with each other. A turning arm 11 is supported to be turnable for the turning angle α₂ by means of a shaft 9 in the horizontal direction. Meanwhile, the turning arm 11 is driven to be turned by means of a motor, not shown, to be described subsequently. A balancing mechanism 13 is also provided in association with the turning arm 11 for the purpose of balancing the turned state of the turning arm. The balancing mechanism 13 comprises a tension spring, for example, not shown, so that the same may be turned together with the cylindrical rotating member 4. A turning arm 17 is supported to be turnable with respect to the arm 11, i.e. for the turning angle α₃ by means of a shaft 15 in parallel with the shaft 9 at the end of the turning arm 11. The turning arm 17 is driven to be turned by means of a motor, not shown, to be described subsequently. A turning wrist 21 is supported to be turnable with respect to the turning arm 17, i.e. for the turning angle α₄ by means of the shaft 19 in parallel with the shaft 9 at one free end of the turning arm 17. The wrist 21 is driven to be turned about the shaft 19 by means of a motor, not shown, to be described subsequently. A rotating shaft 23 for supporting a torch fixture 25 is supported by the wrist 21 so as to be rotatable about the same shaft with respect to the wrist 21. The shaft 23 is driven to be rotated with respect to the wrist 21, i.e. for the rotating angle α₅ by means of a motor, not shown, to be described subsequently. A welding torch 27 is fixed to the torch fixture 25. Thus, the automatic welding apparatus is adapted such that the attitude of the welding torch 27 and the tip end, i.e. the position of the welding point P are controlled by controlling the respective angles α₁, α₂, α₃, α₄ and α₅ of the rotating member 5, the turning arm 11, the turning arm 17, the wrist 21, and the rotating shaft 23, respectively. Fig. 2 is a block diagram showing an outline of one embodiment of the present invention. The embodiment shown comprises an operation panel 100. The operation panel 100 comprises a mode selecting switch 101 for commanding in which operation mode the automatic welding apparatus is to be operated. The mode selecting switch 101 is structured to select any mode among a manual mode M, a test mode T and an automatic mode A. The operation panel 100 further comprises depression button switches 103, 105, 107 and 109. The depression button switch 103 is adapted to afford a start command of the automatic mode and also to afford a teaching command in the manual mode. The depression button switches 105, 107 and 109 are each operated in commanding to the automatic welding apparatus a linear interpolating operation, a weaving operation and an arcuate interpolating operation, respectively. A speed setting unit 111 is also provided. The speed setting unit 111 is used to command the speed of movement of the welding torch 27 and thus of the welding point P. The operation panel 100 is provided with manual switches 119, 121, 123, 125 and 127; and 129, 131, 133, 135 and 137 of two groups. The switches 119 to 127 are operated to control the position of the welding apparatus in terms of the rectangular or orthogonal coordinates system, i.e. the XYZ system. On the other hand, the switches 129 to 137 are used to directly control the respective turning angles α₁ to α₅, i.e. control the α system. Therefore, the operation panel 100 is also provided with a system selecting switch 117 for selectively enabling the group of the switches 119 to 127 or the group of the switches 129 to 137. Accordingly, by turning the system selecting switch 117 to the left, as viewed in Fig. 2, the group of the manual switches 119 to 127 is enabled, and by turning the switch 117 to the right, the group of the manual switches 129 to 137 is enabled. These manual switches 119 to 127 and 127 to 137 can each assume three positions, wherein the position shown by the solid line in Fig. 2 is a neutral position. The switches 119, 121 and 123 are used to control the X axis, the Y axis and the Z axis, respectively, wherein the direction away from the origin point of the rectangular coordinates is defined as the upward direction U and the direction toward the origin point of the rectangular coordinates is defined as the downward direction D. The switch 125 is used to control an orientation angle  of the welding torch 27 and the switch 127 is used to control an attitude angle ϑ of the welding torch 27. These switches 125 and 127 can be used to control the angles  and ϑ associated with the welding torch in the clockwise direction C or the counterclockwise direction CC, respectively. Likewise, the manual switches 129 to 137 of the α system can also be used to control the turning angles α₁ to α₅, respectively, of the respectively arms or the shafts, in the clockwise direction C or the counterclockwise direction CC. A display lamp 113 and a depression button switch 115 provided on the operation panel 100 constitute one feature of the embodiment shown. More specifically, the display lamp 113 is energized to be turned on when the turning arms and the rotating shafts are in a predetermined zone to be described subsequently (or a critical zone), thereby to notify an operator of the same. Accordingly, the display lamp 113 may be replaced by a buzzer for raising an alarm by way of an audible sound or alternatively both may be used similtaneously. The depression button switch 115 is used to set a state of a given turning arm and another turning arm associated therewith, i.e. a first state or a second state. More specifically, the bending direction of the respective turning arms is reversed such as from the first state to the second state or from the second state to the first state, the depression button switch 115 is operated. These first and second states will be described subsequently. Data is exchanged through an interface, not shown, between the operation panel 100 including the above described components and a data bus 55. The data bus 55 is coupled to a central processing unit 31 constituting a control means and a memory 33. The memory 33 comprises a read only memory for storing a system program and a user program of the central processing unit 31 and a random access memory having storing regions and flag regions required for making an arithmetic operation and other processing by the central processing unit 31. The data bus 55 is coupled to a plurality of (in the embodiment shown, five corresponding to the five turning angles α₁ to α₅) driving circuits 351, 352, 353, 354 and 355 and a plurality of (in the embodiment shown, five) incremental encoders 531, 532, 533, 534 and 535. Referring to Fig. 2, the driving circuit 351 is illustrated in more detail representing the others. Although the structure of the driving circuit 351 is described here, it is pointed out that the remaining driving circuits 352 to 355 are also similarly structured. The driving circuit 351 comprises a commanded position buffer 37 for storing commanded position information obtained from the central processing unit 31, and a feedback counter 39 for counting the pulse signal obtained from the corresponding incremental encoder 531. The content in the commanded position buffer 37 and the content in the feeedback counter 39 are applied to a substractor 41 as a minuend and a subtrahend, respectively. The output of the substractor 41 is applied to a digital/analog converter 43. Accordingly, the digital/analog converter 43 provides a voltage signal associated with a difference between the commanded position and the current position. The output from the digital/analog converter 43 is applied through a servoamplifier 45 and a command limiter 47 to a servomotor 49 as a driving signal. The output of the command limiter 47 is further applied to a null signal circuit 51. The null signal is a zero signal obtained from the servoamplifier 45 when the position is controlled by the servo system and is obtained in the region adjacent to the target position or at the timing when the motor 49 is about to be brought to a stop. Accordingly, the output of the null signal detecting circuit 51 is applied through the data bus 55 to the central processing unit 31 as a signal representing that the object being controlled by means of the servomotor 49 has reached the commanded position loaded in the commanded position buffer 37. Since the structure was described in the foregoing, now the operation of the embodiment shown in Fig. 2 and thus of Fig. 1 will be described in the following with reference to the flow diagrams shown in Figs. 3 to 5 and the diagrams shown in Figs. 6 to 14. At the outset the manual mode for the teaching operation will be described. The central processing unit 31 comprises a timer for receiving a clock from a clock source provided therein and the timer is responsive to the clock to generate an output per each predetermined time period. The central processing unit 31 is responsive to the output from the timer to be interrupted thereby at the step S1. At the first step S3 it is determined whether the manual switches 119, 121, 123, 125 and 127 of the respective axes of the operation panel 100 have all been brought to a neutral position. In other words, at the step S3 it is detected whether any of these manual switches 119 to 127 has been operated. Meanwhile, in the manual mode, in most cases the welding line of the workpiece is adapted to extend in the right angle direction when the command is given in the rectangular coordinates system and therefore it is easier for an operator to move the torch 27 along the welding line and also to make an interpolating operation. Therefore, the system selecting switch 117 provided in the operation panel 100 is in advance turned to the XYZ system. Then at the step S5 the central processing unit 31 is responsive to the signal from the operation panel 100 to increase or decrease the commanded value (the fundamental amount) corresponding to the above described timer time period based on the operation direction (U or D or C or CC) of the operated manual switch and the speed as set in the speed setting unit 111. Then at the step S7 it is determined whether the commanded position as a result of accumulation is in the critical zone. Now the "critical zone" will be described. Considering the turning arms 11 and 17, for example, in Fig. 1, the state that can be assumed by these arms 11 and 17 is as shown in Fig. 6. Referring to Fig. 6, (A) shows a state in which the arms 11 and 17 are aligned almost in a line with respect to the shaft 15. (B) in Fig. 6 shows a state of the arms 11 and 17 in which the arms 11 and 17 are bent with the shaft 15 upward, which state is just as shown in Fig. 1. The state as shown in Fig. 6(B) is referred to as a first state (or an up state (U)). Fig. 6(C) shows a state which is opposite to that shown in Fig. 6(B). The state shown in Fig. 6(C) is referred to as a second state (or a down state (D)). Fig. 6(D) shows a state similar to that shown in Fig. 6(B) of the first state but having smaller bending of the arms 11 and 17 as compared with the first state shown in Fig. 6(B). Likewise, Fig. 6(E) shows a state of a very small bending as compared with the second state shown in Fig. 6(C). The states shown in (D) and (E) in Fig. 6 may be handled as almost the same as the state shown in Fig. 6(A). By the term "critical zone", the case of a very small bending of two arms as shown in (D) and (E) in Fig. 6 or the case of no bending of two arms as shown in Fig. 6(A) is meant, in which case the zone has a given minor width. Thus, the states as shown in (A), (D) and (E) in Fig. 6 are referred to as "a state in the critical zone". Meanwhile, the state shown in (D) in Fig. 6 is referred to as "a critical zone up state (Cu)" for convenience and the state shown in (E) in Fig. 6 is referred to as "a critical zone down state (Cd)". Meanwhile, such critical zone and the state may be likewise considered with respect to the wrist 21 and the shaft 23 as well. More specifically, considering the wrist 21 and the shaft 23, i.e. the turning angle α₄ and the rotation angle α₅, two states can be assumed as described above, in the case of the same torch attitude such as the case where control is made to a state in parallel with the vertical axis. Such two states are the position of ″27′″ shown by the two dotted line and the position of ″27″″ shown by the two dotted line in Fig. 1. For convenience the state as shown at the position of ″27″″ is referred to as the first state (U) and the state shown as ″27″′ is referred to as the second state (D). Meanwhile, in the figure the tip end positions of the torches 27′ and 27″ are different; however, if it is desired that these brought to the same welding point position, the other shafts and the turning arms may be properly set. As is seen from Fig. 1, in the embodiment shown the axis of the torch 27 is fixed at 45° with respect to the axis α₅. However, it could happen that such angle be desirably changed depending on the shape and the like of the workpiece. Therefore, the embodiment shown has been adapted such that the angle of the axis of the torch 27 with respect to the axis of the horizontal direction of the rectangular coordinates system may be arbitrarily and changeably controlled from the state (minimum) to 90° (maximum) shown in Fig. 1. In the embodiment shown the position of ″27″ shown by the solid line in Fig. 1 is set as the center of the critical zone. Accordingly, it is adapted such that in the case where it is desired to change as necessary the state from the position of ″27′″ (the second state), for example, to the position of ″27″″ (the first state), such state can not be changed unless the position of ″27″ (the critical zone) is necessarily passed. Meanwhile, the critical zone has a given width as described previously and the critical zone up (Cu) is selected to be a range from the position shown by the solid line to the position dislocated to the ″27″″ side in Fig. 1, while the opposite case is set as the critical zone down (Cd). At the step S7 the central processing unit 31 determines whether the relation of such two arms is in the critical zone. The reason why it is determined at the step S7 whether the relation of the two arms is in the critical zone or not may be described as follows. More specifically, the embodiment shown has been defined such that in order to reverse the first state (or the (U) state) shown in (B) in Fig. 6 to the second state (or the (D) state) shown (C) in Fig. 6, once the critical zone must be commanded and be taught. The reason is that if reversion is made outside the critical zone then the movement of the tip end of the arm is indefinite and collision with a workpiece and the like could occur. If and when it is determined at the step S7 that the current commanded value is in the critical zone, the central processing unit 31 writes the logic one in the critical zone flag CZF included in the random access memory of the memory 33, whereby the flag CZF is set at the step S9. Then at the following step S11 the central processing unit 31 determines whether the previously commanded value was in the critical zone. The decision at the step S11 can be performed by checking the content in the flag CZF previously taught. Than at the step S13 the central processing unit 31 determines whether a state reversion command is available, i.e. whether the depression button switch 115 of the operation panel 100 has been operated. More specifically, in the case where the state before entering into the critical zone was the first state (U) and the same need be changed to the second state (D), the reversion switch 115 is operated. More specifically, if the state reversion is necessary, the switch 115 is depressed with the lamp 113 in a lit state. Upon detection of the reversion command, the central processing unit 31 reverses the up-down flag UDF at the following step S17. The flag UDF is selected such that the logic one is written in the case of the state of (B) in Fig. 6, for example, and the logic zero is written in the case of the state of (C) in Fig. 6, in example. On the other hand, if it is determined at the step S7 that the commanded value at this time is not in the critical zone, at the following step S15 the logic zero is written in the critical zone flag CZF, thereby to reset the same. Thereafter as in the case of passage of the step S17, the positional information is calculated on the articulated system, i.e. α₁ to α₅, in accordance with a situation of the up-down flag UDF. More specifically, in the embodiment shown the command is given in the XYZ system and calculation is made of the α₁ to α₅ system only in the case where drivings are performed in actuality by the driving circuits. The central processing unit 31 provides the positional information of the α₁ to α₅ system calculated at the previous step S19 to the respective corresponding driving circuits 351, 352, 353, 354 and 355. The respective driving circuits 351 to 355 are responsive to the command from the central processing unit 31 to control α₁, α₂, α₃, α₄ and α₅ shown in Fig. 1. Such control is performed per each timer time period. In the case of the teaching operation, the start button 103 of the operation panel 100 is depressed. More specifically, the mode selection switch 101 is turned to the manual mode M and the start button 103 is depressed, whereby the teaching operation of the central processing unit 31 is interrupted. When the teaching operation is interrupted in the central processing unit 31, the positional information and the states of the respective flags CZF and UDF at that time are stored in the predetermined storing areas of the memory 33 (Fig. 4). The positional information being taught at that time is the absolute coordinate system (XYZ system). The reason is that the absolute coordinates system is easier of being operated and is preferred in arithmetic operation for the interpolating control, as described previously. Now referring to Figs. 7 to 14, the coordinates conversion from the XYZ system to the α₁ to the α₅ system will be described. In the embodiment shown the central processing unit 31 may comprise a microcomputer. Recently a microcomputer of an enhanced performance and a high speed operation has become available. Therefore, the embodiment shown has been adapted such that a normal calculation is performed with accuracy in lieu of a conventional approximate calculation processing. Fig. 7 diagrammatically shows an outline of the Fig. 1 automatic welding apparatus, α₁ to α₅ in Fig. 7 correspond to those in Fig. 1. Referring to Fig. 7, a₃ denotes a length component from the lower end of the fixing member 1 to the shaft 9, a₂ denotes the length from the shaft 9 to the shaft 15, a₃ denotes a length component from the shaft 15 to the shaft 19, a₄ denotes a length component from the shaft 19 to the point B where the extension of the welding torch 27 and the extension of the wrist 21 intersect. The point F denotes the portion of the shaft 15, the point Q denotes the position of the shaft 19, and the point P denotes the tip end of the welding torch 27, i.e. the welding point. The angle α₁ denotes the rotating angle of the rotating member 5, α₂ denotes the turning angle of the turning arm 11, and α₃ denotes the turning angle of the turning arm 17. The angle α₄ denotes the turning angle of the wrist 21 in terms of the angle with respect to the vertical axis. The angle α₅ denotes the rotating angle of the shaft 23 set to be 0° in the vertical axis direction. Fig. 8 is a view diagrammatically showing a state of the apparatus as shown in Figs. 1 and 7 as viewed from the top. Referring to Fig. 8, the "absolute coordinates system" means the cartesian or rectangular coordinates system with the approximate center at the lower end of the fixing member 1 (Fig. 1) as deemed as the origin point of the coordinate axes. On the other hand, the "robot system" means the cartesian or rectangular coordinates system with a given point of the apparatus deemed as the origin point. Furthermore, the "torch system" means the cartesian or rectangular coordinates system with the point B in Fig. 7 as deemed with the origin point. Meanwhile, Fig. 9 is a view showing in detail the portion between the points Q and B, wherein the angle component α₆ is constant. The cartesian or rectangular coordinates system here is represented by the respective translation axis components and the angle components, i.e. (x, y, z, , ϑ), while the articulated coordinates system is represented by the angle components, i.e. α₁, α₂, α₃, α₄, α₅). When the position of the rectangular coordinates system of the respective points F, Q and P when the respective angles α₁ to α₅ are given in Fig. 7, the X axis component, Fx, the Y axis component Fy and the Z axis component Fz of the point F may be expressed by the following equations. Fx= -e₁sinα₁ + a₂sinα₂ · cosα₁ Fy= e₁cosα₁ + a₂sinα₂ · sinα₁ Fz=a₁ + a₂cosα₂ Likewise, the respective axis components Qx, Qy, and Qz of the point Q and the respective axis components Bx, By, and Bz of the point B may be expressed by the following equations. Qx=Fx+a₃sin(α₂+α₃) · cosα₁ Qy= Fy+a₃sin(α₂+α₃) · sinα₁ Qz=Fz+a₃cos(α₂+α₃) Bx=Qx+a₄sinα₄ · cosα₁ By=Qy+a₄sinα₄ · sinα₁ Bz=Qz+a₄cosα₄ where α₄=α₂+α₃+α 4E . In order to evaluate the respective axis components of the point P and the orientation angle  and the attitude angle ϑ of the welding torch 27, the coordinates conversion from the robot system to the torch system at the point Q is made. Meanwhile, in the following equations "c i " means "cosα i " and "s i " means "sinα i ". For the purpose of the above described coordinates conversion, the following equation (1) is given. In order to evaluate the position of the welding point P, (α β γ 1)=(0 0 -a₅ 0) is given. Then, the respective axis components Px, Py and Pz of the point P may be expressed by the following equations. Px= -a₅(c₁c₄c₅s₆-s₁s₅s₆+c₁s₄c₆) + Bx Py=-a₅(s₁c₄c₅s₆+c₁s₅s₆+s₁s₄c₆)+By Pz=-a₅(-s₄c₅s₆+c₄c₆)+Bz By coordinating these, the following equations are obtained. In order to evaluate the angles  and ϑ of the welding torch 27, (α, β γ 1)=(0 0 1 0) is substituted in the above described equation (1), whereupon the direction cosines (tx, ty, tz) of the respective axes are obtained. obtained. tx=c₁c₄c₅s₆-s₁s₅s₆+c₁s₄c₆ ty=s₁c₄c₅s₆+c₁s₅s₆+s₁s₄c₆ tz=c₄c₆-s₄c₅s₆ txy=(tx²+ty²) 1/2 The angles  and ϑ of the welding torch are obtained as follows: =tan⁻¹( ty tx ) ϑ=tan⁻¹( txy tz ) By coordinating these equations with respect to the points F and Q, the following equations are obtained. Fx=a₂s₂c₁ -e₁s₁ Fy=a₂s₂s₁ +e₁c₁ Fz=a₂c₂+a₁ Qx=a₃s₂+₃c₁+a₂s₂c₁-e₁s₁ Qy=a₃s₂+₃s₁ +a₂s₂s₁ +e₁c₁ Qz=a₃c₂+₃+a₂c₂+a₁ Thus the positional information of the respective points in the rectangular coordinates system (the robot system) is obtained. Now the coordinates conversion from the rectangular coordinates system (the robot system) to the articulated coordinates system is considered with reference to Figs. 10 to 14. The target position on the occasion of the teaching and the interpolating control is given as that of the point P. Accordingly, it is necessary to calculate the driving amounts of the respective turning shafts based on the rectangular coordinates system. By evaluating the coordinates of the extended point B of the welding torch 27 from (Px, Py, Pz, , ϑ), the respective axis components Bx, By and Bz of the point B may be obtained by the following equations. Bx= Px+a₅sinϑcos By=Py+a₅sinϑsin Bz=Pz+a₅cosϑ Based on the above described Bx, By, Bz, the respective components W1, W2 and W3 in Fig. 10 may be obtained by the following equations. W1=tan⁻¹( By Bx ) W2=(By²+Bx²-e₁²) 1/2 W3=tan⁻¹( e 1 W2 ) Accordingly, the angle α₁ is given by the following equation. α₁ =W1-W3 Now the point Q is evaluated from the given torch angles , ϑ and α₁. See Fig. 11. In this case, conversion is made from the (α β γ) system to the (x′ y′ z′) system. Then the intersecting point of the circle of α²+β²=e₃², γ= -a₈ and the plane of y′=0. Meanwhile, referring to the equations set forth in the following, "ϑ c ," denotes "cosϑ" and "ϑ s " denotes "sinϑ". Likewise, " c " denotes "cos" and " s " denotes "sin". Accordingly, α, β and γ are given by the following equations. α=ϑ c  c x′-ϑ c  s y′-ϑ s z′ β= s x′+ c y′ γ=ϑ s  c x′-ϑ c  s y′+ϑ c z′ From y′=0, α, β and γ may be expressed as follows: α=ϑ c  c x′-ϑ s z′ β= s x′ γ=ϑ s  c x′+ϑ c z′ From γ=-a₈, the following equation (2) is obtained and from α²+β²=e₃² the following equation (3) is obtained. ϑ s  c x′+ϑ c z′+a₈=0 ϑ c ² c ²x′²-2ϑ c  c ϑ s x′z′+ϑ s ²z′²+ s ²x′²=e₃² By substituting z′= -(ϑ s  c x′+a 8 ) ϑ c in the above described equation (3), the following equation is obtained. ( c ²+ϑ c ² c ²)x′²+2a₈ϑ s  c x′+(a₈²ϑ s ²-e₃2²ϑ c ²)=0 The disciminant WD in the above described equation may be obtained as follows: Accordingly, if and when the value of the discriminant WD is minus, this means that the point Q does not exist. On the other hand, assuming the following equations. WA=  c ²+ϑ c ² s ² WD=a₈ϑ s  c WC=a₈²ϑ s ²-e₃²ϑ c ² Then the x′ coordinates of the point Q is given by the following equation. x′= WB±(WB 2 -WA×WC) 1/2 WA The value of z′ corresponding thereto is determined by the following equation. z′= -(ϑ s  c x′+a 2 ) ϑ c On the other hand, assuming that x′ is evaluated in the region of ϑ≦45° and z′ is evaluated in the region of ϑ>45°, then x′ =-(ϑ c z′+a₈)/ϑ s  c , is obtained from the above described equation (2) and the same is substituted in the above described equation (3). Then, the following equation is obtained. ( c ²+ϑ c ² s ²)z′²+2a₈ϑ c z′+ c ²(a₈²ϑ c ²-e₃²ϑ s ²)+a₈² s ²=0 Assuming the following equations in the same manner as done in x′ evaluating: Wa= c ²+ϑ c ² s ² Wb= a₈ϑ c Wc= c ²(a₈²ϑ c ²-e₃²ϑ s ²)+a₈² s ² Then the discriminant WD is obtained by the following equation. WD=Wb²-Wa×Wc Accordingly, the X axis component Qx and the Z axis component Qz of the point Q are given by the following equations. Qz=z′= -(Wb± WD) Wa Qx=x′= -(ϑ c z′+a 8 ) ϑ s  c In either case, the point Q assumes two points of Q₁(x₁′, z₁′), Q₂(x₂′ z₂′) in the coordinates. These two different points correspond to the first state and the second state, respectively. This will be described later. The angles α₄ and α₅ are determined from the coordinates (z′, y′, z′) of the robot system and the coordinates (Qx′, Qy′, Qz′) of the point Q with the point B deemed as the origin point. Since Qy′=0, α₄ is given by the following equation. α₄=tan⁻¹ (-Qx) (-Qz) In order to evaluate the angle α₅, (x″, y″, z″) are further obtained from the previous robot coordinates system (x′, y′, z′). Then (α β γ)=(0 0 -1) is assumed in the (x″, y″, z″) system. Accordingly, x″ and y″ are given by the following equations. x″=-c₄ c ϑ s +s₄ϑ c y″= s ϑ s Assuming that the reference line of the angle α₅ is away from the vertical line by the angle as shown in Fig. 12, the angle α₅ is given by the following equation. α₅=tan⁻¹(-  s ϑ s c 4  c ϑ s -s 4 ϑ c ) When the position of the point Q is evaluated in the absolute coordinate system in order to evaluate the angles α₂ and α₃, the respective axis components Qx, Qy, Qz of the Q are evaluated by the following equations. Qx=Bx+x′cosα₁ Qy=By+x′sinα₁ Qz=Bz+z′ On the other hand, since the point G (see Fig. 14) is (-e₁sinα₁, e₁cosα₁, a₁), the length components I₁, I₂ and the angle component W1 are expressed by the following equations. I₁={(Qx+e₁s₁)²+(Qy-e₁c₁)²} 1/2 I₂={I₁²+(Qz-a₁)²} 1/2 W1′=tan⁻¹( Qz-a 1 I 1 ) Assuming WA=(a₂²+I₂²-a₃²)/2a₂I₂, then the angle component W2′ is given by the following equation. W2′=cos⁻¹(WA)=tan⁻¹{ (1-WA 2 ) 1/2 WA } Furthermore, assuming WB=(a₂²+a₃²-I₂²)/2a₂a₃, then the angle component W3′ is given by the following equation. W3′=tan⁻¹{ (1-WB 2 ) 1/2 WB } Accordingly, the angles α₂ and α₃ are given by the following equations. α₂= π 2 -W1±W2 α₃= ± (π- W3) Thus, conversion from the rectangular coordinates in the articulated coordinates is made; however, as described previously, in the embodiment shown the angles α₅ and α₄ and α₂ and α₃ can be selected in two ways, respectively. Therefore, in calculating the positional information in the α₁ to α₅ system at the step S19 of the flow diagram shown in Fig. 3, calculation is made in accordance with the state of the up-down flag UDF. More specifically, in the case whers the flag UDF is the logic one, calculation is made of the above described angles α₂ to α₅ so that the first state (U) is attained, whereas in the case where the flag UDF is the logic zero conversely calculation is made so that the second state (D) is attained. Now the operation of the automatic mode of the embodiment shown in Fig. 2 and thus in Fig. 1 will be described with reference to Fig. 5. In the case of the automatic mode, the mode selecting switch 101 in the operation panel 100 is turned to the automatic mode A. Then the start button 103 is depressed. The central processing unit 31 reads the target positional information previously taught from the memory 33 at the step S31. Then it is determined at the step S33 whether the critical zone flag CZF has been set based on the read teaching information. More specifically, at the step S33 it is determined whether the target value just read is within the critical zone shown in Fig. 6. In the case where the target position at this time is not in the critical zone, the central processing unit 31 determines at the following step S35 whether the previous up-down flag UDF is the same as the current up-down flag UDF. More specifically, at the step S35 it is determined whether it is necessary to reverse the state between the previous target value and the current target value. In the case where reversion is necessary, i.e. in the case where the previous flag and the current flag are different, then at the following step S37 it is determined whether the previous commanded value was in the critical zone. In the case where it is determined at the step S37 that the previous commanded value is not the critical zone, this means that such reversion of the state cannot be made and processed as an error. In the case where the previous commanded value is in the critical zone, the central processing unit 31 is responsive to the up-down flag UDF included in the teaching information just read out to determine the state at the step S39. Thus it would be appreciated that the case where the state can be reversed is very limited. Now the cases where such reversion can be made will be described with reference to table. Referring to table, A ○, B ○, C ○, and D ○ correspond to A ○, B ○, C ○ and D ○ in the Fig. 5 flow diagram. More specifically, referring to the Fig. 5 flow diagram, as the cases of becoming A ○ the eight cases as marked × in the table may be considered; as the cases of becoming B ○ the four cases may be considered; and as the cases of becoming C ○ the two cases may be considered. Out of them the cases in whuch the state may be reversed, i.e. the cases of becoming D ○ are only two cases or states. More specifically, one of them is the case in which the previous state is the critical zone up (Cu) and the current state is the second state (D) and the flag UDF indicates the logic zero, i.e. the second state (D) and the other of the above described two cases is the case in which the previous state is the critical zone down (Cd) and the current state is the first state (U) and the flag UDF indicates the logic one, i.e. the first state (U). Meanwhile, such reversible conditions may be changed or increased as necessary. Thus at the step S39 the state is reversed where possible. Referring to Fig. 5, as in the cases of A ○ and B ○, at the step S41 a preparatory calculation is made. The preparatory calculation step is aimed to make calculation necessary for an interpolating control, for example. Such an interpolating control may be a linear interpolation, an arcuate interpolation or the like. However, since such interpolating control is well known to those skilled in the art, the same will be briefly described. More specifically, in the case of a linear interpolation, successive interpolation pitches of inner interpolation or outer interpolation are calculated based on the commanded speeds with respect to the two points taught in the XYZ system. In the case of the interpolation of the turning and attitude of the torch, equiangular interpolation is individually performed with respect to each of the angles  and ϑ of the welding torch 27. As regards the position in the case of the arcuate interpolation, a plane including a circle is determined from the three points given in the XYZ system and the center point and the radius are evaluated on the above described plane, whereupon the central angle is interpolated and the respective interpolation pitches on the arcuate curve are evaluated in the XYZ system. Thus other preparatory calculations are performed for the purpose of interpolation. Thereafter the central processing unit 31 makes at the step S41 the successive interpolating points based on the interpolation pitches evaluated by the preparatory calculations. Then at the following step S45 the positions of the welding point P in the α₁ to α₅ system are calculated in accordance with the up-down flag UDF forced or just read out at the previous step S39. The driving circuits 351 to 355 of the respective axes (angles) drive the respective servomotors based on the postional information thus calculated. At the same time the central processing unit 31 determines at the step S49 whether the interpolating points calculated at the above described step S43 has reached the target position initially taught. If the said target position has not yet been reached, at the step S43 the interpolating points are in succession calculated. If and when the target point has been reached as a result of calculation of the interpolating points, it is determined at the step S51 whether the work has been completed, i.e. the welding work has been completed, based on the null signal obtained from the respective driving circuits 351 to 355 of the successive output driving. If and when it is determined that the work has been completed, then a series of automatic mode operation is terminated, whereas otherwise the program returns to the step S31 to read a new target value. At the step S47 the successive interpolating points may be commanded at each expected timing based on the said speeds or the same may be commanded in accordance with the above described null signal. Various manners in which the two states can be assumed at the same position in the articulated robot may be considered. For example, the turning arm 17 in Fig. 1 can be provided to be turnable by the shaft which is orthogonal to the shaft 9 with respect to the turning arm 11. In addition, in Fig. 1, for example, although the shaft 23 is provided to be rotatable with respect to the turning wrist 21, conversely the turning wrist 21 may be a rotating shaft and a tuning shaft may be provided at the end of the wrist 21. More specifcally, if there are three articulations, then a control to any positions can be made and in such a case, if a target position is determined, various types of two states that can be assumed may be readily considered. It is pointed out that the present invention can be applied to any of such manners. Referring to Fig. 1; the wrist 21 is provided to be articulated to the turning arm 17. However, such base point need not be necessarily position controlled by way of an articulation type control and alternatively a control may be made in the rectangular coordinates system. For example, a position control may be made in the rectangular coordinates system up to the point or axis corresponding to the shaft 19 in Fig. 1, whereupon a control may be made of the wrist 21 and the shaft 23 in the articulated coordinates system. By thus employing both the rectangular coordinates system and the articulated coordinates system, such employment would be advantageous from the standpoint of inertia as compared with a case where a control is made all in the articulated coordinates system shown in Fig. 1. Fig. 15 is a perspective view of the above described other embodiment of an articulated robot. Fig.16 is a view showing an internal structure. Figs. 17 to 21 are views showing driving systems of the respective axes α₁, to α₅. First referring to Fig. 15, the embodiment will be described. In Fig.15, like portions have been denoted by like reference characters used in Fig. 1. The cylindrical base 3 is provided on the fixing member 1 and the rotating member 4 is rotatably provided at the top end thereof. The turning angle α₁ is controlled with respect to the rotating member 4. The supporting member 7 is provided on the rotating member 4 and the arm 11 is turnably supported by the supporting member 7. The arm 11 is controlled with respect to the turning angle α₂. The arm 17 turnably provided at the tip end of the arm 11 is controlled with respect to the turning angle α₃. The turning wrist 21 turnably provided at the tip end of the arm 17 is controlled with respect to the turning angle α₄. The rotating shaft 23 supports the torch fixture 25 and is supported to be coaxially rotatable with the wrist 21 and is controlled with respect to the rotating angle α₅. Now reFerring to Fig.16 the internal structure of Fig. 15 embodiment will be described. Referring to Fig.16, the numerals in the order of 300, the reference numerals in the order of 400, the reference numerals in the order of 500. the reference numerals in the order of 600 and the reference numerals in the order of 700 denote those components associated with the respective turning angles α₁, α₂, α₃, α₄ and α₅, respectively. The motor 301 may comprise a well-known direct current servomotor and corresponds to the motor 49 in Fig. 2. The motor 301 is provided such that the output shaft may be in parallel with the rotating member 4. The output shaft of the motor 301 is integrally provided with a pulley 302. A well-known tachometer generator 303 and incremental shaft encoder 304 are provided at the side opposite to the output shaft of the motor 302. On the other hand, a driven pulley 305 being mated with the pulley 302 is provided in association with the rotating member 4. A belt 306 is entrained between the driven pulley 305 and the pulley 302, so that the driven pulley 305 is rotatingly driven by the driving force of the motor 301. A brake 307 and a reduction gear 308 are coupled to the driven pulley 305. The reduction gear 308 may comprise a well-known "harmonic drive (trademark)" having a reduction ratio of approximately 1 100 The output casing of the reduction gear 308 is formed integral with the rotating member 4 and the above described pulley 305 is provided on the input shaft of the reduction gear 308. In the embodiment shown, the belt and pulley may be a well-known toothed belt such as timing belt and a toothed pulley engageable with the timing belt such as a timing pulley. Although not shown in detail, a dog is suitably provided on the outer periphery of the cylinder at the side of the output of the reduction gear 308. Three sets of microswitches, not shown, are provided at predetermined positions of the rotating member 4 in association with and so as to be engageable with the dog. The origin point signal associated with the turning angle α₁ and the both end signal or the turning angle α₁ are obtained by these microswitches. A motor 401 is provided rearward of the motor 301. The motor 401 is aimed to turn the arm 11 and a pulley 402 is integrally provided to the output shaft of the motor 401. A driven pulley 405 being mated with the pulley 402 is provided. A belt 406 is set between the pulley 402 and the driven pulley 405. A tachometer generator 403 and an incremental shaft encoder 404 are associatedly provided at the side opposite to the output shaft of the motor 401. The driven pulley 405 is journaled to be rotatable on the rotating member 4. More specifically, a reduction gear 408 is provided with the output casing thereof journaled on the rotating member 4 and a pulley 405 and a brake 407 are provided on the input shaft thereof. The output casing of the reduction gear 408 is formed with a groove in the circumferential direction. Weight balancing means 13′ for the arm 11 (corresponding to the balancer 13 in Fig. 1) is provided on the rotating member 4. The balancers 13′ are structured such that one end of a tension spring is fixed in the cylinder and a wire is extended from the tip end of the spring. The tip end of the wire is fixed to a portion of the groove on the above described output casing. As a result, the rotation moment in the clockwise direction due to the weight of the arm 11 is balanced as a function of a spring force. Although not shown, a dog is provided at a suitable position on the peripheral surface of the output casing of the reduction gear 408. On the other hand, three sets of microswitches, not shown, are provided at predetermined positions of the rotating member 4 so as to be engageable with the dog. The origin point signal of the turning angle α₂ of the arm 11 and the both end signal of the range of the turning angle α₂ are obtained by these microswitches. A counter shaft is journaled, although not shown, in the output casing of the reduction gear 408 and driven pulleys 505 and 509 and a brake 507 are provided on the counter shaft. Meanwhile, in the embodiment shown, the counter shaft is journaled inside the output casing of the reduction gear 408. However, if there is a margin in space, alternatively such counter shaft may be directly journaled by the rotating member 4. On the other hand, a motor 501 is provided rearward of the motor 401. The motor 501 is aimed to control the turning angle α₃ of the arm 17. A pulley 502 is integrally provided to the output shaft of the motor 501 and a tachometer generator 503 and an incremental shaft encoder 504 are associatedly provided at the side opposite to the output shaft thereof. A belt 507 is set between the pulley 502 and the above described driven pulley 505, so that the driven pulley 505 and thus the above described counter shaft are rotatingly driven by the motor 501. On the other hand, a reduction gear 508 having the output shaft journaled at a suitable position is provided on the arm 17. A driven pulley 510 is integrally provided to the input shaft of the reduction gear 508. A belt 511 is set between the pulley 509 and the driven pulley 510. The belt 511 is set with a suitable tension by means of the two tension pulleys 512 provided on the arm 11. Meanwhile, although not shown in detail, a suitable dog is also provided to the output casing of the previously described reduction gear 508. Three sets of microswitches, not shown, are then provided at predetermined positions in the arm 17 so as to be engageable with the dog, not shown. The origin point signal of the turning angle α₃ and the both end signal of the range of the turning angle α₃ of the arm 17 are obtained by these microswitches. Two driving mechanisms 600 and 700 are provided at the rear end of the arm 17. The driving mechanism 600 is used for controlling the turning angle α₄ of the shaft 23.The driving mechanism 600 comprises a motor 601 and a pulley 602 is integrally provided to the output shaft of the motor 601. A reduction gear 608 is provided rearward of the motor 601 and a driven pulley 605 is integrally coupled to the input shaft of the reduction gear 608. A belt 606 is set between the pulley 602 and the driven pulley 605. A tension pulley 614 is associatedly provided with the belt 606. A tachometer generator 603 and an incremental shaft encoder 604 are coupled to the tension pulley 614. A chain sprocket 615 is integrally provided to the output shaft of the reduction gear 608. On the other hand, a chain sprocket 617 is journaled at the tip end of the arm 17. A chain 618 is set between the chain sprockets 615 and 617. A tension sprocket 616 is toothed with the chain 618. Although the chain 618 is formed as endless, the midway portion not engaging with the sprocket may be replaced by rods 619 and 620. More specifically, the chain 618 comprises the rods 619 and 620 and a chain portion coupled therebetween. A sliding guide, not shown, is provided in the arm 17 in conjunction with these rods 619 and 620. Dogs 619a and 620a are provided in the rods 619 and 620 and these are fixed such that the axial directional positions may be adjustable by means of a screw means, now shown. Microswitches 621 and 622 engageable with the dog 619a are provided at suitable positions of the arm 17. The microswitch 623 engageable with the dog 620a is provided at a suitable position of the arm 17. The microswitch 622 generates the origin point signal of the turning angle α₄ and the microswitches 621 and 623 provides the both-end signals of the range of the turning angle α₄. The driving mechanism 700 comprises a motor 701 and is structured in the manner similar to the above described driving mechanism 600 and is used for controlling the rotating angle α₅. A more detailed description of the driving mechanism 700 will be omitted. A chain 718 is set between the chain sprocket 715 included in the driving mechanism 700 and the chain sprocket 717 provided at the tip end of the arm 17. The chain 718 is also formed as endless as similar to the previously described chain 618 but the midway portion thereof where the same is not engaged with the sprocket are coupled to the rods 719 and 720. A guide, not shown, is provided associated with the rod 719. Three microswitches 721, 722 and 723 are provided at suitable positions of the arm 17 to be engageable with the rod 719. The microswitch 722 provides the origin point signal of the rotating angle α₅ and the microswitches 721 and 723 provide the both end signals of the range of the turning angle α₅. The rotating shaft 23 is coaxially provided to the wrist 21. More specifically, the rotating shaft 23 has a bevel gear 725 at one end and is journaled by the wrist 21. The bevel gear 725 is toothed with a bevel gear 724 being rotated together with the chain sprocket 717. Accordingly, the bevel gear 724 is driven by the driving mechanism 700, whereby the rotating angle α₅ of the rotating shaft 23 is controlled. Now referring to Figs. 17 to 21, the manner of controlling the respective turning angles α₁ to α₅ will be described. As shown in Fig. 17, the turning angle α₁ is controlled by the motor 301. More specifically, the motor 301 is energized and the driving force thereof is supplied through the pulley 302, the belt 306 and the pulley 305 to the reduction gear 308. The rotation driving input is reduced by the reduction gear 308 and the output from the reduction gear 308 is transmitted to the upper end of the base 3. However, since the base 3 has been fixed, the rotating member 4 is rotated with the output from the reduction gear 308. In order to fix the turning angle α₁, therefore, the motor 301 is deenergized while the brake 307 is enabled. In the event that the rotating member 4 is rotated to exceed the range of the turning angle α₁ due to some accident, the brake 307 is automatically actuated with the signal from the above described microswitch, not shown. Thus, the turning angle α₁ is controlled by the motor 301. Now referring to Fig. 18, a control of the turning angle α₂ will be described. The turning angle α₂ is controlled by the motor 401. More specifically, the driving force of the motor 401 is transmitted through the pulley 402, the belt 406 and the pulley 405 to the reduction gear 408 and the arm 11 is turned with the reduced output obtained from the reduction gear 408. At that time the rotational moment in the clockwise direction of the arm 11 is balanced by means of the balancer 13′. The turning angle α₂ is kept constant by deenergizing the motor 401 and by actuating the brake 407. Emergency stop is effected by the microswitch, not shown. The turning angle α₃ of the arm 17 is controlled by the motor 501 as shown in Fig. 19. More specifically, the driving force of the motor 501 is transmitted through the pulley 502, the belt 506, the pulleys 505 and 509, the belt 511 and the pulley 510 to the reduction gear 508. The arm 17 is turned with the output shaft of the reduction gear 508. At that time, a suitable tension is applied to the belt 511 by means of the tension pulleys 512. The turning angle α₃ is kept constant by deenergizing the motor 501 and by actuating the brake 507 and emergency stop is effected by the microswitch, not shown. As shown in Fig. 20 the turning angle α₄ of the wrist 21 is controlled by the drivng mechanism 600. More specifically, the chain sprocket 615 is driven by the reduction gear 608 included in the driving mechanism 600 and the driving force thereof is transmitted through the chain 618 to the chain sprocket 617. Thus the wrist 21 directly coupled to the chain sprocket 617 is turned. In such a case, emergency stop is effected by the microswitches 621 and 623. Furthermore. as shown in Fig. 21, the rotating angle α₅ of the rotating shaft 23 is controlled by the driving mechanism 700. More specifically, the driving force of the driving mechanism 700 is transmitted to the chain sprocket 717 and the bevel gear 724 is rotated together with the chain sprocket 717. The bevel gear 725 toothed with the bevel gear 724 is accordingly turned and as a result the rotating angle α₅ of the rotating shaft 23 is controlled by the driving mechanism 700. In such a case, emergency stop is effected by the microswitches 721 and 723. Meanwhile, it should be appreciated that the above described incremental shaft encoder corresponds to the components 531 to 535 shown in Fig. 2. The angular information of the respective angles α₁ to α₅ is fed back from these incremental shaft encoders. The incremental shaft encoder fails to have the origin point indicating function by itself and suitably receives the origin point information by means of the microswitches of the above described respectives axes, whereupon theorigin point adjustment of the corresponding control systems are made. The tension of the belt and chain is suitably adjusted by means of the fixing position of the corresponding motor, the tension pulley, or the tension sprocket or the like. Accordingly, a slack of the belt and chain can be eliminated and accordingly a noise due to operation of these components can be prevented from occurring. By utilizing the timing belt and the timing pulley, a slip can be prevented and as a result precise control can be made. Thus, according to the embodiments shown in Figs.16 to 21, unique advantages set forth in the following can be brought about. More specifcally, since the turning mechanism is implemented not with a conventional parallelogram link mechanism but by means of a belt setting means, the range of the respective angles can be drastically increased as compared with a conventional one. Since a driven pulley is provided in the input shaft of the reduction machine, a tension of the belt can be decreased and a slacking amount can be decreased. As a result, a control of the turning angle of the respective arms can be made with high precision. Since a motor as a prime mover is provided rearward, a desired collision with an operator and a workpiece is prevented even when the rotating member is turned in association with the turning angle α₁. In addition, since a rod is employed in conjunction with the chain, thereby to shorten substantially the length of the chain portions, a slacking amount of such chain can be decreased and accordingly a control of the turning angles α₄ and α₅ can be made with precision. Furthermore, since the driving mechanisms 600 and 700 including the motors are used also as a balance weight of the arm 17, a motor of unnecessarily large power need not be used as a prime mover for the turning angle α₃. It should be understood that in the specification and the appended claims the term "an articulated robot" should be construed to mean any type of robots having an articulated control system at least in a part of a control system of the robot. More specifcally, even in the case where a major control system is a cartesian or rectangular coordinates system and an articulated control system is provided at the tip end thereof, the present invention can be equally applicable insofar as an object being controlled in the articulated control system can assume two different states. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims: An articulated robot comprising an arm assembly (11,15,17,19,21,25,27) including a pair of mutually articulated arms (11,17) capable of supporting an object (25,27), drive means (49;301,401,501,601,701) for driving the arm assembly to shift the object, and control means (Fig. 2) for controlling said drive means, said control means including teaching means (31,200) whereby orthogonal coordinate data defining a position or attitude of the object can be produced and stored by the control means to allow the control means to control the drive means in such a manner as to cause the arm assembly to shift the object to that position or attitude, said arm assembly being able to assume at least two different states of bending for a position or attitude of the object defined by said orthogonal coordinate data, the articulation angle between the arms being different in the respective states, characterised in that: said teaching means (31,100) includes means (115) for enabling selection between the different bending states of the arm assembly and said control means include storage means for enabling the control means to store state indication data (UDF) forming an indication of which of the states has been selected, in addition to said orthogonal coordinate data, when said teaching means is operated to enable teaching of a point, said control means being operable, when the robot is to move the object to a defined position or attitude, to instruct a desired inversion of the bending state of the arm assembly if, and only if, the stored state indication data (UDF) for a present taught point differs from the stored state indication data (UDF) for the previous taught point and the arm assembly was within a predetermined critical zone for said previous taught point, said critical zone comprising bending states in which the two mutually articulated arms are aligned with one another or are displaced out of alignment by no more than a very small angle, whereby when it is desired that the robot should move the object from a first position or attitude, in which the arm assembly is in one bending state outside the critical zone, to a second position or attitude in which the arm assembly is in a different bending state, but also outside the critical zone, then it is necessary that the robot be taught an intermediate position or attitude for which the arm assembly would be within the said critical zone. An articulated robot in accordance with claim 1, wherein means (S11) are provided for inhibiting said selection means (115) from selecting a different bending state if the current position of the arms and the previously taught point do not lie in the critical zone. An articulated robot in accordance with any preceding claim, wherein: said teaching means (31,100) comprises entry means (119,121,123,125,127) for entering said orthogonal coordinate data defining said position or attitude, and said control means (Fig. 2) comprises coordinates converting means (S41,S43,S45) responsive to said orthogonal coordinate data for converting said data into command information for an articulated system for achieving said articulation angle. An articulated robot in accordance with any preceding claim, wherein: said selection means comprises a state reversing switch (115) for reversing said state. An articulated robot in accordance with any preceding claim, wherein: said control means (Fig. 2) comprises interpolating means (S43), said interpolating means making an interpolating operation based on orthogonal coordinate data. An articulated robot in accordance with any preceding claim which further comprises: a supporting member (7) for pivotally supporting the proximal end of one (11) of said arms (11, 17) by means of a first shaft (9), the other (17) of said arms having its proximal end pivoted at the distal end of said first arm by means of a second shaft (15) which is parallel with said first shaft, first and second prime movers (401, 501) provided to said supporting member for controlling the turning angle of said arms, each said prime mover being provided rearward of said supporting member such that the output shaft thereof may be in parallel with said first shaft, first power transmitting means (402, 405, 406, 408) including first entraining means (402, 405, 406) for transmitting power from one of said two prime movers (041 ) to one of said arms and a first speed reducing unit (408), and second power transmitting means (508, 509, 510, 511) including second entraining means (509, 510, 511) for transmitting power from the other of said two prime movers (501) to the other of said arms and a second speed reducing unit (508). An articulated robot in accordance with claim 6, wherein: said first entraining means comprises: a first pulley (402) coupled to the output shaft of said one of said prime movers, a second pulley (408) coupled to said one of said arms, and a belt (406) entrained in an endless manner between said first and second pulleys. An articulated robot in accordance with claim 6 or claim 7, which further comprises: a third arm (21) having its proximal end pivoted at the distal end of said other arm (17) by means of a third shaft (617) in parallel with said second shaft (15), and a third prime mover (701) provided in said other arm rearward of said second shaft for controlling said third arm, said third prime mover serving as a balance weight of said other arm. An articulated robot in accordance with claim 8, which further comprises: third power transmitting means (715, 717, 718) for transmitting power from said third prime mover to said third arm (21), and wherein said third power transmitting means comprises: a first chain sprocket (715) having a shaft in parallel with said second shaft (15), a second chain sprocket (717) coupled to the proximal end of said third arm, and a chain (718) entrained in an endless manner between said first and second chain sprockets, said chain incorporating a rigid connecting member (719, 720) at a mid-portion thereof, which does not engage said first and second chain sprockets.

Inventors: NOGUCHI, FUMIO
Applicants: SHIN MEIWA INDUSTRY CO., LTD.
Application year: 1981
Main classification: G05B19
IPC codes: B25J9, B25J19, G05B19