Rotational position detector for robot

Abstract: Disclosed is herein a rotational position detector for a robot which can always accurately detect the rotational positions of each rotational member (7,13,20) based on the output values from each absolute value detector regardless of the rotational conditions of the rotational member. Each absolute value detector (35,36,37) (resolver) is connected to each rotational member such that the ratio of the rotational angle period of the absolute value detector to the rotational angle period of the rotational member is set to be 1 : N (N is an integer larger than 1).

Description: The present invention relates to a rotational position detector according to the preamble of claim 1, and particularly to a rotational position detector for detecting the rotational positions of each arm or wrist member being capable of multiple rotations around the same axis by each absolute value detector. A generic rotational position detector is known from the DE-A-3 720 828. This generic rotational position detector comprises a motor-driven rotational member and absolute value detectors which detect the rotational positions of the rotational member. The absolute value detectors are connected to reduction gears, so that a ratio of the rotational angle period of the absolute value detector to that of the rotational member is 1:N, N being an integer value larger than 1. However, this rotational position detector is directly connected to the rotational member via a reduction gear so that the relation of the angle periods automatically fulfils the condition 1:N, N being an integer, since every reduction gear fulfils this condition. Another conventional detector has such a construction as shown in Fig. 3, wherein a motor 3 rotating a wrist 2 through a reduction gear 1 is connected to a resolver 5 through a reduction gear 4. As the resolver 5, there is used a so-called absolute value detector for outputting the magnitude of a rotational angle in terms of an absolute value signal by each rotation of a detection shaft. The motor 3 is mounted with a resolver 6 (so-called precise resolver) for precisely detecting the rotational positions of the output shaft of the motor 3. When the wrist 2 is rotated by the motor 3, the rotational position of the wrist 2 is detected based on an output signal from the resolver 5. In the aforesaid conventional detector, even when the resolver 5 is rotated by a large number of times, the rotational positions can be continuously detected by counting the rotational number of the resolver 5 or the like. However, for example, when the power is switched off once due to a trouble and is switched on again, there occurs an inconvenience to erroneously detect the rotational positions of the wrist 2 according to an output signals from the resolver 5. This is because of the fact that, as shown in Fig. 4, for the same signal values from the resolver 5 to the wrist 2 capable of multiple rotations, the rotational positions differ from each other, shown as the points A, B and C, depending on the rotational conditions of the wrist 2. Therefore, the rotational angle of the wrist 2 has been limited so that the rotation of the resolver 5 can be kept within one turn for realizing an absolute position detection mechanism in the aforesaid detector. It is an object of the present invention to provide a rotational position detector which can under all conditions accurately detect the rotational position of a rotational member. This object is achieved by the features of claim 1. An advantageous further development is set out in claim 2. According to the invention, each of plural rotational members is respectively assigned to an absolute value detector. The absolute value detectors are directly connected to the motors via reduction gears. Furthermore, reduction gears are provided between the motors and the rotational members. These two reduction gears per unit of rotational member/ absolute value detector are adjusted such that the rotational angle periods of the absolute value detector and the rotational member are 1:N. Thereby it is ensured that the rotational positions of the rotational member with respect to that of its absolute value detector are accurately assigned to an identical value of the output of the absolute value detector in every rotational condition. In the present rotational position detector having the aforesaid construction, when the rotational positions are identical to each other in each rotational member rotated by a large number of times, the signal values outputted from each absolute value detector in compliance with the rotational positions are always identical to each other. In other words, the absolute positions of each rotational member are always accurately detected based on the output signal values from each absolute value detector regardless of the rotational conditions of the rotational member. In the drawings: Fig. 1 is a construction view showing the major portion of a robot including a rotational position detector according to an embodiment of the present invention; Fig. 2 is a graph showing the relation between an output signal value from an resolver (absolute value detector) constituting the rotational position detector shown in Fig. 1, and a rotational position of a wrist member; Fig. 3 is a construction view showing the outline of the major portion of a robot for explaining the background technology of the present invention; and Fig. 4 is a graph regarding a conventional rotational position detector showing the relation between an output signal value from an absolute value detector and a rotational position of a wrist member. The exemplary embodiment according to the present invention will be described in detail with reference to the drawings. The present rotational position detector is nearly similar to the conventional one in the essential construction, except that each resolver is connected to each arm or a wrist member such that the ratio of the rotation angle period of the resolver (so-called absolute value detector) to the rotational angle period of each arm or the wrist member is set to be 1 : N (N is an integer larger than 1 and is selected at 4 in the present embodiment). Fig. 1 is a construction view of a robot including the rotational position detector, wherein a cylindrical first arm 7 is supported by a base 8 so as to be rotatable around an axis α, and which is rotated by a servomotor 9 disposed on the base 8 through a reduction gear 10, and gears 11 and 12. In this case, the gear 11 is identical to the gear 12 in the number of teeth. A cylindrical second arm 13 is supported by the first arm 7 so as to be rotatable around an axis β crossing the axis α, and which is rotated by a servomotor 14 disposed on the base 8, through a reduction gear 15, gears 16 and 17, and bevel gears 18 and 19. In this case, the same number of teeth is selected between the gears 16 and 17, and between the bevel gears 18 and 19, respectively. A wrist member 20 is supported on the extreme end portion of the second arm 13 so as to be rotatable around an axis γ crossing the axis β of the second arm 13, and which is rotated by a servomotor 21 disposed on the base 8, through a reduction gear 22, gears 23 and 24, and bevel gears 25, 26, 27 and 28. In this case, the same number of teeth is selected between the gears 23 and 24, between the bevel gears 25 and 26, and between the bevel gears 27 and 28, respectively. The servomotors 9, 14 and 21 are provided with respective resolvers 29, 30 and 31 for precisely detecting the rotational positions of respective output shafts of the servomotors 9, 14 and 21. Moreover, the servomotors 9, 14 and 21 are connected through reduction gears 32, 33 and 34 to resolvers 35, 36 and 37 (so-called absolute value detectors) for detecting the rotational absolute positions of the first arm 7, the second arm 13 and the wrist member 20. In the present embodiment, respective reduction ratios of the reduction gears 10, 15 and 22 are set to be l/i 1 , respective reduction ratios of reduction gears 32, 33 and 34 are set to be l/i 2 , and i 2 /i 1 is set to be N. In the aforesaid embodiment, therefore, the ratio of the rotational angle periods of the resolvers 35, 36 and 37 to the rotational angle periods of the first arm 7, the second arm 13 and the wrist member 20 becomes 1 : N, respectively Accordingly, for example, in the relation between the resolver 37 and the wrist member 20, if the output signal values from the resolver 37 are identical to each other, respective absolute rotational positions of the wrist member 20 corresponding to the output signals are always accurately shown at an identical value regardless of the rotational conditions of the wrist member. In this case, it is possible to detect the rotational number of the wrist member 20 prior to its positioning at an absolute position by detecting the rotational number of the resolver 37. The relation between the resolver 37 and the wrist member 20 as described in the above can be applied to the relation between the resolver 35 and the first arm 7, and also to the relation between the resolver 36 and the second arm 13. In the present embodiment, therefore, even in a case where the power is once switched off due to a trouble and later it is switched on again, the absolute positions of the first arm 7, the second arm 13 or the wrist member 20 can be always accurately detected based on respective output signal values from the resolver 35, 36 or 37. Disclosed is herein a rotational position detector for a robot which can always accurately detect the rotational positions of each rotational member based on the output values from each absolute value detector regardless of the rotational conditions of the rotational member. Each absolute value detector (resolver) is connected to each rotational member such that the ratio of the rotational angle period of the absolute value detector to the rotational angle period of the rotational member is set to be 1 : N (N is an integer larger than 1).

Claims: A rotational position detector for detecting rotation of rotational members of a robot, comprising a rotational member (12, 17, 24) capable of multiple rotations, a motor (9, 14, 21) for driving said rotational member (12, 17, 24), absolute value detectors (35, 36, 37) for detecting rotational positions of said rotational member (12, 17, 24), reduction gears (32, 33, 34) to which said absolute value detectors (35, 36, 37) are connected, respectively, wherein a ratio of the rotational angle period of said absolute value detector (35, 36, 37) to the rotational angle period of said rotational member (12, 17, 24) is 1:N, where N is an integer larger than 1, characterized in that plural rotational members (12, 17, 24) are respectively connected with each of said absolute value detectors (35, 36, 37), for which purpose said absolute value detectors (35, 36, 37) are directly connected via said reduction gears (32, 33, 34) to said motors (9, 14, 21), respectively, and further reduction gears (10, 15, 22) are provided between said motors and said rotational members (12, 17, 24) wherein said reduction gears (32, 33, 34) of said absolute value detectors (35, 36, 37) and said reduction gears (10, 15, 22) of said rotational members (12, 17, 34) are coordinated such that the ratio of the rotational angle period of said absolute value detectors (35, 36, 37) to the rotational angle period of said respective rotational members (12, 17, 24) is set to be 1:N, so that specific rotational positions of said rotational members (12, 17, 24) are accurately assigned to an identical value of the output signal of said absolute value detectors (35, 36, 37) regardless of how often said rotational members (12, 17, 24) have been rotated. A rotational position detector according to claim 1, characterized in that said plural rotational members (12, 17, 24) are capable of multiple rotations about the same axis.

Inventors: OBATA MITSUYOSHI, TAKAGI NOBORU, OBATA, MITSUYOSHI, TAKAGI, NOBORU, Obata, Mitsuyoshi, c/o Iwaya Plant, KOBE STEEL,LTD, Takagi, Noboru, c/o Iwaya Plant, KOBE STEEL, LTD
Applicants: KOBE STEEL LTD, KABUSHIKI KAISHA KOBE SEIKO SHO
Application year: 1992
Main classification: G01B21
IPC codes: G01B21, G01D5, G05D3, B25J19, B25J9