JP5471482B2 - Parallel link type robot and abnormality detection method thereof - Google Patents

Description

  The present invention relates to a parallel link robot in which a first member and a second member are connected by a plurality of links that expand and contract, and a method for detecting that an abnormality has occurred in link control of the parallel link robot.

  A parallel link robot is known in which a plurality of links are connected in parallel to a first member and a second member. In this specification, a member serving as a base is referred to as a first member, and a swinging member is referred to as a second member. The parallel link robot expands and contracts the link by an actuator, and causes the posture of the second member relative to the first member to follow a desired posture (target posture). The parallel link type robot includes a type that determines the angle of the second member depending on the length of the link, and a type that can determine both the angle and position of the second member. When determining the angle of the second member, there is a type that determines three angles of roll, pitch, and yaw, and a type that determines only an angle around one axis. A typical example of the former is a device called a motion ride capable of controlling a total of six degrees of freedom of the position in the three orthogonal axes and the angle around the three orthogonal axes. As an example of the latter, there is a device for controlling the three degrees of freedom of the plane disclosed in Non-Patent Document 1. The parallel link type robot disclosed in Non-Patent Document 1 can determine the position of the second member in the plane (two degrees of freedom) and the angle around the normal of the plane (one degree of freedom). Further, Patent Document 1 discloses an example in which a parallel link type robot is applied to a human walking assist device.

  In this specification, the “position” and “angle” of the second member are collectively referred to as the “posture”. First, this point will be described. Of the six degrees of freedom in the space in the three orthogonal axes and the angle around the three orthogonal axes, which one of the degrees of freedom to be selected for the second member depends on the mechanism of the parallel link robot. In general robots as well as parallel link robots, the angle and position of the robot tip can be handled equally in positioning control. The term “spatial coordinates” is sometimes used as a term that collectively refers to angles and positions. However, in this specification, the “spatial coordinates” (that is, the angle and / or position) is referred to as “attitude” in consideration of easy understanding. In particular, in this specification, a set of values that define an angle and / or position corresponding to each degree of freedom with respect to the degree of freedom allowed for the second member among the six degrees of freedom of the space is referred to as “attitude”. . For example, when the second member has three degrees of freedom, the posture of the second member is represented by a set of three numerical values that determine each degree of freedom. The angle and / or position that is the control target value of the second member is referred to as a “target posture”.

  In the following, the number of degrees of freedom allowed for the second member is N degrees of freedom. For example, N = 6 in a parallel link robot that can determine all six degrees of freedom of the second member. Note that the degree of freedom N is not limited to six. For example, in the case of a parallel link type robot in which the second member is configured to move on a plane by a link, the degree of freedom N of the second member is two degrees of freedom within the plane and one degree of freedom around the plane perpendicular. This is a total of three degrees of freedom (see, for example, Non-Patent Document 1). Other degrees of freedom are constrained. That is, the degree of freedom N allowed for the second member is 3.

JP 2008-79809 A

Volapod Serirat, Mitsutoshi Sato, “Motion control of a planar 3-DOF parallel link servomechanism using a hydraulic cylinder (1st report)”, Proceedings of the Japan Fluid Power System Society, Vol. 35, No. 2, 8-13 Page, March 2004

  Since the parallel link robot determines the posture of the second member by adjusting the length of the link, each link is provided with a sensor for measuring the length of the link. If the sensor fails, normal link control cannot be performed. In order to prepare for sensor failure, a plurality of sensors may be provided for each link. Providing a plurality of sensors for each link increases costs. The present specification provides a technology for detecting whether or not an abnormality has occurred in link control without using a plurality of sensors in each link, utilizing the characteristics of the structure of the parallel link robot.

  The parallel link type robot includes N links in order to determine the posture of the second member with N degrees of freedom. Each of the N links connects the first member and the second member. In the parallel link type robot, the target posture of the second member is converted into the target length of each link, and the length of each link is controlled so as to match the target length. In the parallel link type robot, if the control cannot be performed normally even with one link, the posture of the second member does not match the target posture even if the length of the other link matches the target length. Therefore, a situation may occur in which the sensor fails and the output data of the sensor indicates a length equal to the target length, but the actual link length is not equal to the target length. In such a case, the output data of all the sensors indicate the respective target lengths, but the posture of the second member does not match the target posture. In order to cope with such a situation, the parallel link type robot disclosed in the present specification further includes another link connecting the first member and the second member in addition to the N links. In order to distinguish “N links” from “other links”, the N links are referred to as main links, and the other links are referred to as auxiliary links. However, the auxiliary link may have the same configuration as the main link. The technology disclosed in this specification detects that an abnormality has occurred in the control of one of the main links from the length of the auxiliary link.

  Each main link includes an actuator for expanding and contracting the main link. In order to control the length of the main link, each main link is also provided with a sensor for measuring the length. The controller of the parallel link type robot controls the length of the main link by the actuator so that the posture of the second member matches the target posture.

  The parallel link type robot disclosed in the present specification includes an auxiliary link connecting the first member and the second member in addition to the N main links. The auxiliary link is provided with a sensor for measuring its length. In order to distinguish the sensor included in the auxiliary link from the sensor included in the main link, the sensor included in the main link may be referred to as a main sensor, and the sensor included in the auxiliary link may be referred to as an auxiliary sensor. However, the main sensor and the auxiliary sensor may be of the same type. The main sensor and the auxiliary sensor may be collectively referred to as “sensor”. Similarly, the main link and the auxiliary link may be collectively referred to as “link”.

  The auxiliary link is configured to be capable of passive expansion and contraction by a force in the link axial direction applied from the outside. For example, the auxiliary link is biased in the extending direction by a spring. The attitude of the second member changes due to active expansion and contraction of the main link, and the length of the auxiliary link passively changes with the attitude change of the second member.

  The technology disclosed in this specification detects whether or not an abnormality has occurred in the control of any main link from the length of the auxiliary link that passively expands and contracts with the movement of the second member. When the length of the auxiliary link measured by the auxiliary sensor is different from the planned length of the auxiliary link when the posture of the second member matches the target posture, an abnormality occurs in the control of one of the main links. Judge that you are doing. If it is determined that an abnormality has occurred, for example, the controller stops the control of the main link. Alternatively, the controller outputs a signal notifying that an abnormality has occurred to the outside.

  The parallel link type robot disclosed in the present specification includes an auxiliary link that connects the first member and the second member in parallel with the main link, in addition to the N main links. Since the number of main links is N with respect to the allowed degrees of freedom N, all the values of the degrees of freedom N are uniquely determined by the N main links. That is, the posture of the second member is uniquely determined. However, in this specification, singular points are not mentioned. When all the main links are normally controlled, the posture of the second member matches the target posture. The technology disclosed in the present specification verifies the posture of the second member that should match the target posture by controlling the length of the N main links based on the length of the auxiliary link. If the length of the auxiliary link is different from the planned length, it is found that one of the main links is not normally controlled. According to the technology disclosed in this specification, it is possible to detect that an abnormality has occurred in the control of any of the main links without providing a plurality of sensors for all the main links.

  The above abnormality detection assumes the following situation. One of the main sensors has failed, and the posture of the second member does not actually match the target posture, but the posture of the second member calculated using the output of the failed main sensor matches the target posture. This is the situation. In such a situation, an abnormality cannot be detected only by the output of the main sensor. The technology disclosed in this specification can detect an abnormality in the control of the main link even in such a situation.

  Instead of comparing the measured length of the auxiliary link with the planned length, it is also preferable to calculate the posture of the second member using the length of the auxiliary link and compare the calculated posture with the target posture. is there. That is, the controller preferably performs the following processing. (1) The posture of the second member is calculated from the total length of N links obtained by adding auxiliary links to the number of main links less than N selected from the N main links. (2) When the calculated posture is different from the target posture, it is determined that an abnormality has occurred in link control. By such processing, it is possible to simultaneously detect how much the actual posture of the second member deviates from the target posture.

  If a control abnormality occurs in any of the main links, it is impossible to continue the control for making the posture of the second member coincide with the target posture. This specification also provides a technique capable of continuing control even when a control abnormality occurs in any of the main links. Therefore, the parallel link type robot includes an actuator on the auxiliary link. The auxiliary link actuator is controlled by the controller and can actively expand and contract the auxiliary link. The controller includes a force control mode in which the auxiliary link is passively expanded and contracted by a force applied in the link axial direction from the outside, and a position control mode in which the auxiliary link is controlled so that the length of the auxiliary link matches the target length. The auxiliary link can be controlled by switching. For example, if the expansion / contraction sliding resistance when the power is shut off is small, the controller can realize the force control mode by shutting off the power of the actuator. Alternatively, the force control mode can also be realized by attaching a force sensor (for example, a load cell) that measures an external force to the auxiliary link and controlling the actuator so that the external force measured by the force sensor is equal to or less than a threshold value close to zero. . Further, the controller is configured to be used for control to switch the auxiliary link to the position control mode so that the posture of the second member matches the target posture when it is determined that an abnormality has occurred in the control of the link. . With the above configuration, when the control of any main link becomes abnormal, the positioning control of the second member can be continued using the auxiliary link. The present specification also proposes a method for identifying a link in which an abnormality has occurred. The method will be described later.

  When the auxiliary link includes an actuator, the structure of the auxiliary link may be the same as that of the main link. That is, the auxiliary link actuator and sensor may be the same as the main link actuator and sensor. That is, the parallel link type robot may have a structure including M main links larger than N with respect to the second member in which N degrees of freedom are allowed. Hereinafter, a method for detecting a link control abnormality in a parallel link robot having such a structure will be described.

  Another technique disclosed in this specification is that an N + M link connects a first member and a second member in parallel, and the second member has an N-degree-of-freedom abnormality in a parallel link robot. It is a method of detection. Here, the N links correspond to main links that are actively expanded and contracted by the actuator. The M links correspond to auxiliary links that passively expand and contract with the expansion and contraction of the main link (with the movement of the second member). This method comprises the following four steps. In the first step, N links are selected from all N + M links. At this time, a combination in which the main link and the auxiliary link are mixed can be taken. In the second step, the attitude of the second member relative to the first member is calculated from the length of the selected link. In the third step, the calculated posture is compared with the target posture of the second member. In the fourth step, the above-described first to third steps are repeated with different link combinations. In the fourth step, when there is a link combination that does not match the link combination whose calculated posture matches the target posture, a link that is not included in the mismatched link combination is specified as a control abnormality occurrence link.

  The reason why the link where the control abnormality has occurred can be specified by the above method is as follows. The premise is that the output data of the main sensor shows a length equal to the target length for the main link where an abnormality has occurred, but the actual link length is not equal to the target length. It is. In the parallel link structure, when one link does not match the target length, the posture of the second member does not match the target posture even if the other links match the target length. For this reason, the calculated posture matches the target posture in the link combination including the link in which an abnormality has occurred, but the calculated posture does not match the target posture in the link combination formed only of normal links. Therefore, by removing links that constitute link combinations whose calculated postures do not match the target postures, it is possible to identify links in which an abnormality has occurred.

  As described above, the auxiliary link may include an actuator in the same manner as the main link. In this case, N + M main links are provided, and the controller may control the M links in the force control mode. In this case, as described above, the posture control of the second member can be continued by switching the link that has been controlled in the force control mode to the position control mode instead of the main link in which an abnormality has occurred.

  This specification provides a technique for detecting that a control abnormality has occurred in any of the links in a parallel link robot.

1 is a schematic plan view of a parallel link type robot according to a first embodiment. The flowchart figure of attitude | position control is shown. The flowchart figure of an abnormality detection process is shown. The typical perspective view of the parallel link type robot of 2nd Example is shown. The flowchart figure of the abnormality detection process of the robot of 2nd Example is shown.

  FIG. 1 is a schematic plan view of a parallel link robot 100 according to the first embodiment. Hereinafter, for simplicity, the parallel link robot 100 is simply referred to as the robot 100. The robot 100 is a three-degree-of-freedom parallel link robot that positions the second member 12 in the XY plane. The second member 12 can move in the XY plane and cannot deviate from the XY plane. That is, the degree of freedom N allowed for the second member 12 is N = 3. The robot 100 can control a total of three degrees of freedom of the position of the second member 12 in the XY plane and the rotation angle around the normal of the XY plane. The combination of the position of the second member 12 in the XY plane and the rotation angle around the vertical line of the XY plane corresponds to the “posture” of the second member 12.

  The second member 12 is connected to the first member 11 via three main links 13 a, 13 b and 13 c and one auxiliary link 15. Hereinafter, when the three main links are collectively referred to, “main link 13” is described. When one main link is indicated without distinction, “main link 13” is described. Each of the three main links 13 connects the first member 11 and the second member 12. The three main links 13 are arranged in parallel. Each main link 13 has one end pivotably connected to the first member 11 and the other end pivotally connected to the second member 12. Each main link 13 includes a linear actuator 14 for adjusting the link length, and a linear encoder 17a for measuring the length of the main link. The linear encoder 17a corresponds to the main sensor. The linear actuator 14 has a structure in which, for example, a ball screw and a worm gear are combined, and is driven by a motor. The sensor data of the linear encoder 17a is sent to the controller 20. The controller 20 controls the three main links 13 (linear actuators 14) based on the sensor data of the linear encoder 17a so that the posture of the second member 12 matches the target posture. Hereinafter, the linear actuator is simply referred to as “actuator”, and the linear encoder is simply referred to as “encoder”.

  The robot 100 further includes an auxiliary link 15. The auxiliary link 15 connects the first member 11 and the second member 12 in parallel with the main link 13. One end of the auxiliary link 15 is swingably connected to the first member 11, and the other end is swingably connected to the second member 12. The auxiliary link 15 includes a spring 16 that urges the auxiliary link 15 in a direction of extending its length. The auxiliary link 15 is passively expanded and contracted by the urging force of the spring 16 according to the movement of the second member 12, that is, by an external force applied in the axial direction. The biasing force of the spring 16 is negligibly small compared to the force output from the actuator 14. Accordingly, the auxiliary link 15 expands and contracts “passively” in accordance with the movement of the second member 12. Further, the auxiliary link 15 includes an encoder 17b for measuring the length thereof. The encoder 17b corresponds to an auxiliary sensor. The sensor data of the encoder 17b is also sent to the controller 20. The encoder 17a included in the main link 13 and the encoder 17b included in the auxiliary link 15 are the same. However, in order to distinguish the encoder (main sensor) included in the main link 13 and the encoder (auxiliary sensor) included in the auxiliary link, Are suffixed with "a" and "b".

  The robot 100 determines the posture of the second member 12 with three degrees of freedom by adjusting the lengths of the three main links 13. FIG. 2 shows a flowchart of attitude control executed by the controller 20. The controller 20 acquires the sensor data (main link length data) of each encoder 17a (S22). Next, the controller 20 calculates the target length of each main link 13 for realizing the target posture from the target posture of the second member 12 (S23). A conversion formula for obtaining the (target) length of each link from the (target) posture of the second member of the parallel link type robot is commonly called “reverse conversion” in robot engineering. A conversion formula for obtaining the posture of the second member from the length of each main link is commonly called “forward conversion”. “Forward conversion” and “inverse conversion” depend on the mechanical structure of the robot. Since these conversion formulas are well known in the field of robotics, their explanation is omitted. The controller 20 drives each actuator 14 so that the length of each main link 13 measured by the encoder 17a (main sensor) matches the target length (S24). In other words, the controller 20 controls the length of the main link 13 by the actuator 14 so that the posture of the second member 12 matches the target posture.

  While controlling the main link, the controller 20 monitors whether or not the main link is normally controlled based on the length of the auxiliary link 15. Here, the degree of freedom N allowed for the second member 12 is “3”, and the number of main links 13 for moving the second member 12 is also three, so the posture of the second member 12 is It is uniquely determined by the length of the three main links. The auxiliary link 15 expands and contracts passively according to the movement of the second member 12. The auxiliary link 15 does not contribute to the posture determination of the second member 12. The robot 100 uses an auxiliary link that does not contribute to the determination of the posture of the second member 12 to monitor whether a control abnormality has occurred in the main link that actively expands and contracts in order to determine the posture of the second member 12. To do.

  FIG. 3 shows a flowchart of the main link control abnormality detection process. First, the controller 20 acquires data of the encoder 17b (auxiliary sensor) included in the auxiliary link 15 (S32). That is, the controller 20 acquires the length of the auxiliary link 15. Next, the controller 20 calculates a planned length to be realized by the auxiliary link 15 when it is assumed that the posture of the second member 12 matches the target posture (S33). The planned length is obtained by inversely transforming the target posture.

  Next, the controller 20 determines whether or not the planned length calculated in step S33 matches the length (measured length) of the auxiliary link 15 acquired in step S32 (S34). When the planned length matches the measured length (S34: YES), it means that the target posture is realized by the three main links 13. In this case, the controller 20 ends the abnormality detection process. On the other hand, when the planned length does not match the measured length (S34: NO), it means that the posture of the second member 12 does not match the target posture. When the branch determination in S34 is “NO”, the controller 20 determines that an abnormality has occurred in the control of any of the main links. In this case, the controller 20 stops the control of the actuator 14 (S36) and outputs a signal notifying that an abnormality has occurred (S37). For example, the controller 20 outputs a signal for lighting a lamp that notifies the occurrence of an abnormality.

  A case will be described where the measured length of the auxiliary link 15 does not match the planned length in step S34 of FIG. As described above, in this case, it means that the posture of the second member 12 does not match the target posture. As described above together with the flowchart shown in FIG. 2, the length of each main link 13 is controlled so that the posture of the second member 12 matches the target posture. When all the main sensors (encoders 17a) are functioning normally and the posture of the second member 12 does not match the target posture for some reason, the target length and measurement are performed at any of the main links. The length deviation remains. Since the deviation remains even if the actuator is controlled, the controller 20 can detect that the second member 12 does not match the target posture. However, one of the main sensors (encoder 17a) has failed, and the main link length does not actually match the target length, but the output of the main sensor indicates that the main link length is the target length. Is not detected from the output of the main sensor. Therefore, in the robot 100 of the embodiment, the attitude of the second member 12 is calculated using the sensor data of the auxiliary sensor (encoder 17b) of the auxiliary link 15, and the output of the main sensor (encoder 17a) is monitored. doing. By providing the auxiliary link 15, the robot 100 can detect a type of control abnormality that cannot be detected by the main sensor alone.

  An alternative process of the abnormality detection process shown in FIG. 3 will be described. Instead of calculating the planned length of the auxiliary link in step S33, the controller 20 adds the auxiliary link to the two main links selected from the three main links 13, and calculates the first link length from the total three link lengths. The attitude of the two members 12 may be calculated. In this case, in step S34, if the calculated posture is different from the target posture, it is determined that a link control abnormality has occurred. Such a method is basically equivalent to the abnormality detection method according to the flowchart of FIG. 3 in terms of detecting abnormality of the main sensor based on the measurement length of the auxiliary link. However, this method has an advantage that it is possible to simultaneously detect how much the deviation between the target posture and the actual posture is. It is also preferable that the controller 20 is configured to determine that an abnormality has occurred when the deviation between the target posture and the actual posture exceeds a predetermined threshold.

  The above-described method is expressed with respect to the degree of freedom N as follows. The controller 20 calculates the posture of the second member from the total N link lengths obtained by adding auxiliary links to N or less main links selected from the N main links, and the calculated posture is the target. If it is different from the posture, it is determined that an abnormality has occurred. Since the total length of N links including the auxiliary links is used, the posture of the second member having N degrees of freedom can be determined. It should be noted that the above-described abnormality detection method can be applied even when a plurality of auxiliary links are provided.

  Next, the parallel link type robot 200 of the second embodiment will be described. Hereinafter, the parallel link type robot 200 is simply referred to as a robot 200. A schematic perspective view of the robot 200 is shown in FIG. The robot 200 is a three-degree-of-freedom parallel link type robot that can change the rotation angle of each of the three orthogonal axes of the second member 212. Here, the X axis, the Y axis, and the Z axis shown in FIG. 4 correspond to three orthogonal axes. The rotation angle around each axis corresponds to a so-called pitch angle, roll angle, and yaw angle.

  The second member 212 is swingably connected to the tip end of a support 230 extending from the first member 211 via a ball joint. Since the second member 212 is connected to the tip of the column 230 by a ball joint, the second member 212 can swing around each of the three axes. However, the movement of the second member 212 in the translational direction is restricted by the column 230. That is, the degree of freedom N allowed for the second member 212 is N = 3. A combination of rotation angles (pitch angle, roll angle, and yaw angle) around each axis of the second member 212 corresponds to the “posture” of the second member 212. Note that the Z-axis is an axis extending in the longitudinal direction of the column 230, and the X-axis and the Y-axis are axes orthogonal to the Z-axis.

  In the robot 200, four main links 213a, 213b, 213c, and 214d connect the first member 211 and the second member 212, respectively. One end of each main link is swingably connected to the first member 211 via a ball joint, and the other end is swingably connected to the second member 212 via a ball joint. Each main link includes an actuator (linear actuator) 214 that expands and contracts the link, and an encoder (linear encoder) 217 that measures the link length. The encoder 217 is built in the actuator 214 and is not shown. The length of each main link is controlled by the controller 220.

  In the robot 200 having the mechanical structure shown in FIG. 4, when all the main links are simultaneously extended (contracted simultaneously), the second member 212 rotates around the Z axis. By extending some main links and shrinking other main links, the second member 212 rotates about the X or Y axis. In this manner, the robot 200 can match the posture (angle around each axis) of the second member 212 with the target posture. That is, the robot 200 can match the posture of the second member 212 with three degrees of freedom to the target posture.

  One main link 213 a includes a force sensor 218. The force sensor 218 measures a force (external force) applied in the axial direction of the main link 213a. The controller 220 controls the length of the main link 213a so that the external force measured by the force sensor 218 is substantially zero. That is, the main link 213a is force-controlled so as to passively expand and contract according to an external force acting in the axial direction. This is expressed as "the controller 220 controls the main link 213a in the force control mode". On the other hand, the controller 220 can make the posture of the second member 212 coincide with the target posture by appropriately adjusting the lengths of the other three main links 213b, 213c, and 213d. The controller 220 calculates the target length of the main links 213b, 213c, and 213d from the target posture by the inverse transformation described above, and performs control so that each main link matches the target length. This is expressed as “the controller controls the main links 213b, 213c, and 213d in the position control mode”. Since the degree of freedom N of the second member 212 is N = 3, the posture of the second member 212 is uniquely determined by the lengths of the three main links 213b, 213c, and 213d. As described above, the main link 213a is controlled so as to passively expand and contract in accordance with an external force. Therefore, the posture of the second member 212 is changed by the length change of the three main links 213b, 213c, and 213d. As the posture of the second member 212 changes, the length of the main link 213a passively changes.

  In order to distinguish the main link 213a controlled in the force control mode from the other three main links controlled in the position control mode, the main link 213a may be referred to as an “auxiliary link 213a”. Similarly, a sensor (encoder 217) included in the main link 213a may be referred to as an auxiliary sensor. On the other hand, the sensor (encoder 217) of the other three main links controlled in the position control mode may be referred to as a main sensor. In the following description, the main links 213b, 213c, and 213d and the auxiliary link 213a are collectively referred to as “link”. In addition, when the sensor of the main link and the sensor of the auxiliary link are generically named, they are simply referred to as “sensor”.

  FIG. 5 shows a flowchart of processing for detecting a control error of the main link. First, the controller 220 sets “OFF” in the flag (S61). This flag is reset to “ON” when there is a link in which an abnormality has occurred (S66, described later). It should be noted that this flag is a skillful flag for facilitating the processing. The controller 220 acquires sensor data of four links (that is, the length of each link) (S62). Next, the controller 220 selects three links from the four links (S63). The auxiliary link 213a may be included in the selected link. There are four combinations (link combinations) for selecting three links from the four links. As will be described later, the controller 220 repeats the processing from step S63 to S67 for all four link combinations (S67: YES, S63). The controller 220 calculates the attitude of the second member 212 from the lengths of the selected three links (S64). Next, the controller 220 determines whether or not the calculated posture matches the target posture of the second member 212 (S65). If the calculated posture does not match the target posture (S65: NO), it means that a control abnormality has occurred in any of the links. Therefore, the controller 220 sets “ON” in the flag (S66). The controller 220 stores information on whether or not the links constituting each link combination and whether or not the posture calculated by the link combination matches the target posture.

  After the processing from S63 to S67 is performed for all link combinations, if the flag is set to ON, steps S69 and S70 are executed (S68: YES), and if ON is not set, the processing is performed. Is finished (S68: NO). That is, if the flag is set to ON, it indicates that a control error has occurred on any of the main links, and if the flag remains set to OFF, no control error has occurred. Indicates.

  In step S69, the controller 220 identifies the link where the control abnormality has occurred. As described above, the controller 220 stores the links constituting each link combination and whether or not the posture calculated by the link combination matches the target posture. The controller 220 excludes links constituting a link combination in which the calculated posture does not match the target posture from all the links, and specifies the remaining links as abnormality occurrence links. The reason why the anomaly link can be specified in this way is as follows.

  The premise is that the sensor output data indicates the length equal to the target length for the link where the control error has occurred, but the actual link length is not equal to the target length. is there. Also, in a parallel link robot having N main links (links whose length is actively adjusted) for N degrees of freedom, if one link does not match the target length, Even if the link matches the target length, the posture of the second member 212 does not match the target posture. For this reason, the calculated posture matches the target posture in the link combination including the link in which the control abnormality has occurred, but the calculated posture does not match the target posture in the link combination constituted only by normal links. Even if the calculated posture is a link that constitutes a link combination that matches the target posture, when the normal link is combined with another link, the calculated posture does not match the target posture. Therefore, normal links are excluded even if the link constitutes a link combination whose calculated posture matches the target posture. In this way, the process of excluding the links constituting the link combination whose calculated attitude does not match the target attitude is continued, and the link remaining without being excluded is identified as the link in which the control abnormality occurs. .

  The controller 220 cuts off the power of the link in which the control abnormality has occurred (power off), and puts the link into a state of passively expanding and contracting (S69). Then, the controller 220 switches the auxiliary link from the force control mode to the position control mode (S70). In this way, the link in which the control abnormality has occurred is removed from the position control (control for matching the second member 212 to the target posture), and the auxiliary link is switched to the position control, thereby changing the posture of the second member 212 to the target posture. It is possible to continue the control to match the above.

  In the second embodiment, a case where N = 3 is assumed. The technique of the present embodiment can be applied to cases other than N = 3. Also, the present invention can be applied when there are a plurality of auxiliary links. If the degree of freedom is represented by the symbol N and the number of auxiliary links is represented by the symbol M in the flowchart of FIG. In this link control abnormality detection method, N links that are actively expanded and contracted by an actuator connect the first member and the second member in parallel, and the second member is allowed to move in N degrees of freedom. This is a method of detecting a link control abnormality of a parallel link type robot. The method includes the following four steps. First step: N links are selected from N + M links. This step corresponds to step S63 in FIG. Second step: The attitude of the second member relative to the first member is calculated from the length of the selected link. This step corresponds to step S64 in FIG. Third step: The calculated posture is compared with the target posture of the second member. This step corresponds to step S65 in FIG. Fourth step: The first step to the third step are repeated with different link combinations (S67), and there is a link combination that does not match the link combination in which the calculated posture matches the target posture (S66, flag = ON). Then, a link that is not included in the link combination indicating that they do not match is specified as a control abnormality occurrence link (S69).

  Further, in the second embodiment, when the abnormality occurrence link is excluded and attention is paid to the function of continuing the posture control of the second member 212 by the auxiliary link, the characteristics of the robot 200 of the second embodiment can be expressed as follows. . The controller 220 assists by switching between a force control mode in which the auxiliary link is passively expanded and contracted by a force applied from the outside and a position control mode in which the auxiliary link is controlled so that the length of the auxiliary link matches the target length. It is possible to control the link 213a. When the controller 220 detects a control abnormality in any of the links, the controller 220 switches the auxiliary link 213a to the position control mode and uses it for the control to match the posture of the second member with the target posture. Note that the link in which the control abnormality is found is switched from the position control mode to the force control mode.

  The preferred embodiment of the present invention has been described. Points to be noted in the technology disclosed in this specification will be described. In both the first example and the second example, the degree of freedom N allowed for the second member was “3”. The technique disclosed in the present embodiment can be applied to cases other than N = 3. However, naturally, 1 ≦ N ≦ 6. In the robot of the embodiment, each end of the link is connected to the first member and the second member by a ball joint. A so-called universal joint may be used in place of the ball joint.

  In the robot of the second embodiment, a force control mode in which the auxiliary link 213a expands and contracts according to an external force is realized using a force sensor. When the mechanical expansion / contraction sliding resistance of the auxiliary link is small, the auxiliary link can be expanded / contracted according to the external force by cutting off the power supply to the actuator of the auxiliary link. The “force control mode” in this specification includes the case where the link can be passively expanded and contracted by power interruption. For example, when the actuator that expands and contracts the link is an air cylinder, the “force control mode” can be achieved simply by cutting off the power supply to the pump for supplying air.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

11, 211: 1st member 12, 212: 2nd member 13a, 13b, 13c: Main link 14, 214: Linear actuator 15: Auxiliary link 16: Spring 17a, 17b, 217: Linear encoder 20, 220: Controller 100, 200: Parallel link type robot 213a, 213b, 213c, 213d: Link 218: Force sensor 230: Post

Claims (2)

A parallel link type robot capable of controlling the posture of N degrees of freedom of the second member connected to the first member;
N main links each connecting the first member and the second member and extending and contracting by an actuator;
An auxiliary link connecting the first member and the second member and passively expanding and contracting by a force applied from the outside;
A sensor for measuring the length of the auxiliary link;
A controller for controlling the length of the main link by an actuator so that the posture of the second member matches the target posture,
The controller determines that an abnormality has occurred in link control when the length of the auxiliary link measured by the sensor is different from the planned length of the auxiliary link when the posture of the second member matches the target posture. And
The auxiliary link has an actuator that expands and contracts the auxiliary link,
The controller
The auxiliary link is controlled by switching between a force control mode in which the auxiliary link is passively expanded and contracted by a force applied from the outside and a position control mode in which the auxiliary link is controlled so that the length of the auxiliary link matches the target length. Is possible and
A parallel link robot characterized in that, when it is determined that an abnormality has occurred in link control, the auxiliary link is switched to a position control mode and used for control to make the posture of the second member coincide with the target posture . The controller
Calculating the attitude of the second member from the total length of N links obtained by adding auxiliary links to the number of main links less than N selected from the N main links;
2. The parallel link robot according to claim 1, wherein when the calculated posture is different from the target posture, it is determined that an abnormality has occurred in link control.

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