1. Technical Field
The present invention relates to a technique of controlling a multi-jointed manipulator.
2. Description of Related Art
Multi-jointed manipulators have been used in robot arms or the like of industrial or consumer use. Various techniques are already available in association with position control for such manipulators.
As an example, there is a technique using inverse kinematics in which displacements or driving forces of respective joint axes for achieving specific end-point position of a manipulator are determined by computation of inverse kinematics to allow the control to be performed based on the resulting displacement or driving forces.
An example of this related art technique using inverse kinematics is explained with reference to
Referring to
Referring to
In this case, a calculation equation to be generally applied for calculation of position of the hand end 504 in step S52 is expressed as shown by Equation (1):
H=T(θ) (1)
Equation (1) is called kinematic equation for link mechanisms, where H represents a position vector of the hand end and θ represents a displacement vector of the joint axis.
Also, in step S54, a calculation equation generally applied for calculation of displacement-velocity control commands can be expressed as shown by Equation (2):
θc=T−1(Ho) (2)
Equation (2) is called inverse kinematic equation for link mechanisms, where Ho represents a target position vector of the hand end for achieving a target trajectory and Δc represents a displacement vector of the joint axis for achieving the target position vector of the hand end. However, since there are some problems, for example, that Equation (2) cannot be uniquely solved for redundant control systems, other calculation methods may be used, in some cases, instead of Equation (2) (see, e.g., Patent Documents 1 and 2).
Related art examples disclosed in Patent Documents 1 and 2 are explained with reference to
In the control method disclosed in Patent Document 1, displacements of the joint axes for achieving hand end position of the manipulator are determined by using either one of two methods as shown in
In the control method disclosed in Patent Document 2, a control section is compelled to do training of inverse kinematics relations so that driving force for an actuator can be calculated. In
There are other methods for performing distributed control without using inverse kinematics (see, e.g., Patent Documents 3, 4).
Related art examples disclosed in Patent Documents 3 and 4 are explained with reference to
In the control method disclosed in Patent Document 3, the manipulator performs control by using partial differentiation of a multivariable evaluation function for each joint angle. Referring to
Referring to
It has been the case that such control using inverse kinematics or distributed control as shown above is performed to fulfill position control of multi-jointed manipulators.
Patent Document 1: Japanese patent application publication No. H07-164360
Patent Document 2: Japanese patent application publication No. H02-054304 A
Patent Document 3: Japanese patent application publication No. H09-207087 A
Patent Document 4: Japanese patent application publication No. 2000-094368 A
However, the conventional control methods, when applied to manipulators that perform operations demanding higher degrees of freedom, encounter the following issues.
The conventional method using inverse kinematics, although applicable to manipulators which are nonredundant and have no nonlinear elements, yet may be incapable of working for intended operations depending on environments. This is because a manipulator state is uniquely determined so that the hand end is disabled from reaching a target position. On the other hand, with redundancy or nonlinear drive elements incorporated for enhancement of the degree of freedom for operations, the inverse kinematic equation, Equation (2), becomes too complicated to uniquely solve, which may lead, in some cases, to an impossibility of control or an enormous quantity of computations that makes it impossible to fulfill real-time control.
In the case of Patent Document 1, constraint conditions are provided for a redundant manipulator by making use of its configuration or reduction in its degree of freedom so as to enable its control. However, since the degree of freedom is limited by the constraint conditions in one aspect, there is a possibility that the workability of the manipulator may be limited. Also, in the case of Patent Document 2, it is possible, by the training of the multilayer neural network, to solve the redundancy, the computational problems due to nonlinear drive elements, or the robustness. However, without any proper setting of parameters or teaching data, it can occur that the training takes much time or computation results do not converge, resulting in a difficulty in adaptation.
Further, in the methods using inverse kinematics, since displacements or driving forces for all the joints for the reach to a control target is uniquely determined in either case, an occurrence of immobility of one joint due to effects of ambient environments or some failure could make it impossible to fulfill the total position control.
Patent Document 3 is capable of distributed control uniform over the individual joints independent of the configuration of the manipulator. However, the evaluation function or computation processing therefor needs to be set according to the configuration of the manipulator or the contents of its working operation, where it can be the case that the working operation cannot be fulfilled depending on the evaluation function. Also, Patent Document 4 is capable of performing distributed control uniform over the individual joints independently of the configuration of the manipulator. However, since the load on a joint varies depending not only on the position and posture but also on the trajectory or the tool to be set on the manipulator in working or the like, there is a need for preliminarily registering load thresholds for the joints by teaching or training for each working operation, so that unexpected circumstances could not be managed.
These and other issues associated with manipulator control would occur not only when position control for the hand end of the manipulator is performed but also when force control for the hand end is performed.
Accordingly, an object of the present invention, lying in solving the above-described issues, is to provide a control method and a control system for manipulators capable of easily and flexibly achieving the control even with redundancy or nonlinear drive elements involved, independently of such uncertainties as ambient environments or failures of the joint axes.
In accomplishing the above object, the present invention has the following constitutions.
According to a first aspect of the present invention, there is provided a control method for a manipulator having a plurality of joint axes, comprising:
a first step for measuring a difference between a parameter and a target value for an end portion of the manipulator;
a second step for transmitting joint information including joint displacements and joint velocities of the plurality of joint axes, and difference information bearing the difference, to joint control sections for the joint axes, respectively; and
a third step for correcting parameters of the joint axes independently of one another by the joint control sections, respectively, based on the joint information and the difference information, wherein
the first to third steps are iterated until the parameter of the end portion reaches to within a set range including the target value.
According to a second aspect of the present invention, there is provided a control method for a manipulator having a plurality of joint axes, comprising:
a first step for measuring a positional difference between an end position of the manipulator and a target position;
a second step for transmitting joint information including joint displacements and joint velocities of the plurality of joint axes, and positional difference information bearing the positional difference, to joint control sections for the joint axes, respectively; and
a third step for correcting the joint displacements and the joint velocities of the joint axes independently of one another by the joint control sections, respectively, based on the joint information and the positional difference information, wherein
the first to third steps are iterated until the end position reaches to within a set range including the target position.
According to a third aspect of the present invention, there is provided the control method for a manipulator as defined in the second aspect, wherein
based on the information as to the joint displacements and joint velocities acquired from the plurality of joint axes, the joint information including the joint displacements and joint velocities of the plurality of joint axes is prepared on the joint axis basis, and
thereafter, the second step is executed.
According to a fourth aspect of the present invention, there is provided the control method for a manipulator as defined in the second aspect, wherein
in the second step, information including a Jacobian matrix computed by using the joint displacements and the joint velocities as well as an end velocity of the manipulator is transmitted on the joint axis basis, while information as to a deviation vector of the end position with respect to the target position is transmitted as the positional difference information on the joint axis basis,
in the third step, by using the end velocity, the joint velocities of the joint axes, and the Jacobian matrix, a motion vector for the end position is computed based on the joint velocity vectors of the joint axes, and the joint velocity vector is corrected on the joint axis basis so that the motion vector approaches the deviation vector.
According to a fifth aspect of the present invention, there is provided the control method for a manipulator as defined in the second aspect, wherein
in the second step, information including information as to a velocity ratio of an upper-limit value of an end velocity to an actual end velocity, the end velocity being set in correspondence to a distance between the end position and the target position, is transmitted to the joint axes, and
in the third step, the joint velocities are corrected on the joint axis basis in response to the velocity ratio by the plurality of joint control sections.
According to a sixth aspect of the present invention, there is provided the control method for a manipulator as defined in the third aspect, wherein
when all of acquired joint velocities of the joint axes are 0, the position of the target position or the joint velocity is temporarily changed, and
thereafter, the second step is executed.
According to a seventh aspect of the present invention, there is provided the control method for a manipulator as defined in the second aspect, wherein
acquired identification information as to joints owned by the joint axis is unified, by which a change in connection states of the plurality of joint axes is detected.
According to an eighth aspect of the present invention, there is provided the control method for a manipulator as defined in the second aspect, wherein after identification information as to the plurality of joint axes is transmitted from the total control section to the plurality of joint control sections, control for the joint axes is executed in the plurality of joint control sections only when previously stored identification information as to the joint control sections' own joints coincides with the transmitted identification information.
According to a ninth aspect of the present invention, there is provided a control method for a manipulator having a plurality of joint axes, comprising:
a first step for measuring a force difference between a contact force applied to an end portion of the manipulator and a target contact force;
a second step for transmitting joint information including joint displacements and joint velocities of the plurality of joint axes, as well as force difference information bearing the force difference, to joint control sections for the joint axes, respectively; and
a third step for, based on information including the joint displacements and the joint velocities of the plurality of joint axes as well as on information bearing the force difference, correcting the joint displacements and the joint velocities for the joint axes in the joint control sections independently of one another on the joint axis basis, wherein
the first to third steps are iterated until the contact force applied to the end portion reaches to within a set range including the target contact force.
According to a tenth aspect of the present invention, there is provided the control method for a manipulator as defined in the ninth aspect, wherein
based on the information as to the acquired joint displacements and joint velocities of the plurality of joint axes, the information including the joint displacements and the joint velocities of the plurality of joint axes is prepared on the joint axis basis; and
thereafter, the second step is executed.
According to an 11th aspect of the present invention, there is provided the control method for a manipulator as defined in ninth aspect, wherein
in the first step, a positional difference between a position of the end portion and a target position is further measured,
in the second step, information including a Jacobian matrix computed by using the joint displacements and the joint velocities as well as information including an end velocity of the manipulator is transmitted to the plurality of joint axes, while information as to a deviation vector of the end portion with respect to the target position and a target contact force is prepared, and information as to a total difference which is a result of adding to the positional difference an equivalent positional difference obtained by equivalently converting the force difference into a positional difference is transmitted, and
in the third step, by using the end velocity, the joint velocities of the joint axes, and the Jacobian matrix, a motion vector for the end position is computed based on the joint velocity vectors of the joint axes, and the joint velocity vectors are corrected on an joint axis basis so that the motion vector approaches the deviation vector.
According to a 12th aspect of the present invention, there is provided a control system for a manipulator having a plurality of joint axes, comprising:
a measuring device for measuring a difference between a parameter and a target value for an end portion of the manipulator;
a total control section for controlling the manipulator based on the difference information and information including joint displacements and joint velocities of the plurality of joint axes;
a transmission device for transmitting evaluation result information as to the control from the total control section to the plurality of joint axes; and
a plurality of joint control sections which are provided on the plurality of joint axes, respectively, for correcting parameters of the joint axes independently of one another of the joint axes based on the transmitted evaluation result information thereby controlling driving of the joint axes.
According to a 13th aspect of the present invention, there is provided a control system for manipulator having a plurality of joint axes, comprising:
a measuring device for measuring a positional difference between an end position of the manipulator and a target position;
a total control section for controlling a position of the manipulator based on information bearing the positional difference and information including joint displacements and joint velocities of the plurality of joint axes;
a transmission device for transmitting the position control information from the total control section to the plurality of joint axes; and
a plurality of joint control sections which are provided on the plurality of joint axes, respectively, for correcting the joint displacements and the joint velocities of the joint axes independently of one another of the joint axes based on the transmitted position control information thereby controlling driving of the joint axes.
According to a 14th aspect of the present invention, there is provided the control system for a manipulator as defined in the 13th aspect, wherein the total control section comprises:
a storage device for storing therein joint information including identification information or morphological information as to the joint axes;
a monitoring device for monitoring connection states of the plurality of joint axes based on the joint information stored in the storage device; and
a joint information updating device for updating the joint information stored in the storage device when a change in the connection states of the plurality of joint axes is detected by the monitoring device.
According to a 15th aspect of the present invention, there is provided the control system for a manipulator as defined in the 13th aspect, wherein each of the joint control sections comprises:
a storage device for storing therein joint information including identification information or morphological information as to the joint axes; and
a communication device for notifying the total control section of the joint information stored in the storage device by any of the joint axes being connected to another joint axis.
According to a 16th aspect of the present invention, there is provided a control system for a manipulator having a plurality of joint axes, comprising:
a measuring device for measuring a force difference between a contact force applied to an end portion of the manipulator and a target contact force;
a total control section for performing torque control for the manipulator based on information bearing the force difference and information including joint displacements and joint velocities of all the joint axes;
a transmission device for transmitting the torque control information from the total control section to the plurality of joint axes; and
a plurality of joint control sections which are provided on the plurality of joint axes, respectively, for correcting the joint displacements and the joint velocities of the joint axes independently of one another of the joint axes based on the transmitted torque control information thereby controlling driving of the joint axes.
According to the control method and the control system of manipulators in the present invention described above, since the position control for a control target (a specified range including a control target) is performed independently on a joint-to-joint basis, there occurs neither the problem that the control command value involved in inverse kinematics cannot be uniquely determined nor the problem due to large quantities of computations, even in a manipulator having redundancy or nonlinear drive elements. Thus, the position control of the manipulator can be carried out with reliability.
Also, since there is no need for setting constraint conditions for the computation of inverse kinematics or for limiting the degree of freedom, the control can be carried out while a high degree of freedom is maintained. Furthermore, since the training by data storage is unnecessary as well, the manipulator control can be carried out with ease.
Further, even if some of the articulation joints are disabled from operation due to effects of the ambient environments or failures of the joints, the redundancy is naturally exercised by the other joints individually going toward the control target, making it possible to achieve the control independent of such uncertainties as the ambient environments or failures of the articulation joints.
Consequently, there can be provided a control method and a control system for manipulators capable of easily and flexibly achieving the control even with redundancy or nonlinear drive elements involved, independently of such uncertainties as ambient environments or joint failures.
These and other aspects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which:
Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. Herein below, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Herein below, a control system of a manipulator according to a first embodiment of the present invention, as well as its control method, will be described with reference to the accompanying drawings.
The joint control section 23 includes a measuring device 3s having an encoder or other like sensor and serving for performing measurement of states (joint displacement and joint velocity) of the joint axis 3, and an actuator 3a for driving the joint axis 3. The joint control section 23 also includes a control computation processing device 3c which creates, by computations, information for performing drive control of the actuator 3a based on information inputted from the measuring device 3s and the total evaluation section 20 to perform drive control of the actuator 3a independently of the other joint axes 4-9. It is noted that the measuring device 3s and the actuator 3a are provided on the joint axis 3. Like the joint control section 23, the joint control sections 24-29 also include measuring devices 4s-9s, actuators 4a-9a, and control computation processing devices 4c-9c, respectively. The total evaluation section 20 includes a total evaluation processing device 21.
In the control processing flow of
Next, at step S7, based on the evaluation result and the total-state information as to the manipulator 1 transmitted from the total evaluation section 20, as well as on the joint-displacement and joint-velocity information as to the joints of the joint control sections' own (information measured at step S1), control command values (correction values) for the actuators 3a-9a of the joints own are calculated in the joint control sections 23-29, respectively, independently of the other joint axes (third step). Subsequently, at step S8, based on the calculated control command values, the actuators 3a-9a of the joint control sections' own joints are driven. Thereafter, control processes of the steps S1-S8 are iteratively executed. At step S5, if it is decided from an evaluation result that the hand 18 of the manipulator 1 has reached the control target 19, position control of the manipulator 1 for the control target 19 is completed. It is noted that control processes of the steps S1, S7 and S8 are executed independently of one another by the joint control sections 23-29, respectively, while control processes of the steps S2-S6 are executed by the total evaluation section 20. A sampling time during which the processes of the steps S1-S8 are iterated in the total evaluation section 20 and the joint control sections 23-29 is set to a time period of 10 ms or less, e.g. a time period of about 1 ms. It is noted that such a sampling time setting is determined on a basis of the time taken for the hand 18 of the manipulator 1 to be brought closer to the control target.
As shown in the control processing flow of
A more concrete relationship between the individual control elements in the control system of the manipulator 1 shown in
In the step S5, in which it is decided as an evaluation result whether the hand 18 of the manipulator 1 has reached the control target 19, a decision criterion therefor is whether or not the hand 18 has reached within a specified range including the control target 19, in consideration of control width and errors in the position control.
Now an outlined view of operation of the control system of this first embodiment is shown in
Referring to
Concrete values, evaluation results and control computation methods to be computed in the individual processing steps in the control method of the first embodiment are set as follows as an example. First, in the control processing flowchart of
Position of the hand 18 can be determined by substituting displacements of all the joints into the forward kinematic equation of Equation (1). Further, differentiating both sides of Equation (1) yields the following Equation (3):
V=Jω (3)
In Equation (3), V represents a velocity vector of the hand 18, J represents a Jacobian matrix, and ω represents a joint-velocity vector of an joint axis. Accordingly, substituting measured joint velocities of the joint axes into Equation (3) allows the velocity of the hand 18 to be calculated and the Jacobian matrix as well to be calculated simultaneously.
Further, an evaluation result computed in the step S4 of the total evaluation section 20 is given by a deviation vector that connects from the position (end position) of the hand 18 to the control target (target position) 19. this deviation vector is an example of the positional difference.
The deviation vector can be determined by the following Equation (4):
D=G−H (4)
In Equation (4), D represents a deviation vector, and G represents a position vector of the control target.
As the control method for the joint control sections 23-29, a change in a motion vector of the hand 18 due to a change in joint velocity of a targeted joint axis is considered. A velocity vector of the hand 18 created by the joint velocity of the targeted n-th joint (n-th joint axis) can be calculated by using Equation (3) as follows:
Vn=Jωn (5)
In Equation (5), Vn represents a velocity vector of the hand 18 created by the joint velocity of the n-th joint, and con represents a joint velocity vector of an joint axis which has zero velocity changes except the n-th joint element. Accordingly, the motion vector of the hand 18 resulting when the joint velocity of the n-th joint is accelerated or decelerated with a small velocity change a can be expressed by Equation (6) for acceleration and by Equation (7) for deceleration:
V+αn=J(ω+αn) (6)
V−αn=J(ω−αn) (7)
In Equation (6) and Equation (7), V+αn represents a velocity vector of the hand 18 for an acceleration of the n-th joint alone with a velocity change α, V−αn represents a velocity vector of the hand 18 for a deceleration of the n-th joint alone with a velocity change α, and an represents a joint velocity vector of an joint axis which has a velocity change α for the n-th joint alone with zero velocity changes for the other elements.
From Equations (3), (6) and (7), motion vectors of the hand 18 can be calculated for three cases that a current velocity is maintained, accelerated and decelerated, respectively. Therefore, using the following Equation (8), magnitudes of directional components of those deviation vectors are calculated:
C=V·D/|V|×|D| (8)
In Equation (8), C represents a magnitude per unit component of the deviation vector directional components, and it can be understood that given an angle φ formed by the directional vectors of V and D, C=cos φ, where the angle φ becomes smaller and smaller with increasing value of C so that the directions of V and D approach a coincidence with each other. Accordingly, values of C are determined for V, V+αn, and V−αn, respectively, and a joint velocity of the joint axis at which the value of C becomes largest, i.e. the velocity vector of the hand 18 becomes closest to the control target 19, is calculated as the control command value.
Next, a control method for the joint axes 3-9 by the joint control sections 23-29, respectively, is explained with reference to schematic views shown in
Referring to
Referring to
In the control method described above, without controlling the velocity of the manipulator 1 as a whole, i.e. without directly controlling the velocity of the hand 18, joint velocities of the respective joint axes 3-9 are set. Accordingly, there is a possibility that the velocity of the hand 18 may result in such an abnormally fast one as to lead to a dangerous state or a passage through the control target without stoppage. Thus, the velocity of the hand 18 is limited, for example, as shown in the schematic view of
Referring to
With the addition of such processing, joint velocities of all the joint axes are consequentially decelerated in accordance with the upper-limit velocity, by which the hand 18 is so controlled that an upper limit of velocity of the hand 18 becomes the upper-limit velocity. As the upper-limit velocity declines with increasing closeness to the control target 19, the velocity of the hand 18 is decelerated more and more with increasing closeness of the hand 18 to the control target 19, so that the hand 18 can reliably be stopped at the control target 19.
Another issue to be solved on the manipulator control lies in the singular posture of the manipulator. The term “singular posture” refers to an abnormal posture which causes an error in the manipulator control, it being an important issue of manipulator control how this state is avoided. For an explanation of the singular posture of the manipulator, schematic views showing management for the singular posture of the manipulator 1 in the first embodiment are shown in
Referring first to
Therefore, in this first embodiment, the following two ways are exploited to enable the management for the singular posture, i.e., the escape from the singular posture. In this first embodiment, when joint velocities of all the joint axes 3-9 (joint axes 7-9 in
First, as shown in
Next, the second control method is a method in which the presence or absence of a singular posture is added as a new evaluation result computed in the step S4 of the total evaluation section 20 in
The first embodiment has been described above on a case where evaluation results and the total-state information are transmitted from the total evaluation section 20 to all the joint control sections 23-29 (step S6 of
According to the control method by the control system of the manipulator 1 of the first embodiment, the following various effects can be obtained.
In the control method of the first embodiment, information as to an evaluation result of the total state of the manipulator 1 prepared in the total evaluation section 20 is transmitted to the individual joint control sections 23-29, and then based on the evaluation result information, control command values of the joint control sections' own joints are prepared in the joint control sections 23-29, respectively, independently of the other joint axes. As a result, joint axis basis control exerted independently toward the control target 19 makes it possible to achieve position control. Thus, there occurs neither the problem that the control command value involved in inverse kinematics cannot be uniquely determined nor the problem due to large quantities of computations, even in the manipulator 1 having redundancy or nonlinear drive elements. Also, since there is no need for setting constraint conditions for the computation of inverse kinematics or for limiting the degree of freedom, the control can be carried out while a high degree of freedom is maintained. Furthermore, since the training of operations is unnecessary as well, the manipulator control can be carried out with ease.
Moreover, even if some of the joint axes are disabled from operation due to effects of the ambient environments or failures of the joint axes, the redundancy is naturally exercised by the other joint axes going independently toward the control target 19, making it possible to achieve the position control in a state of robustness against the ambient environments or joint failures. It is noted that the term, robustness, refers to a property that the system characteristics are capable of maintaining functions of the status quo against uncertain variables such as disturbance or design errors. Further, the term ‘failure’ herein refers to a state that an joint axis does not operate regardless of a control command issued to the joint axis because the joint control section that performs operation control for the joint axis or the total evaluation section has not recognized the occurrence of any problem with the objective joint axis.
Furthermore, such problems as an excessive velocity of the hand 18 due to the joint axis basis computation of control command values or a passage of the hand 18 through the control target 19 can be solved by the velocity control of the hand 18 performed by the total evaluation section 20 or the like. Also, the singular posture of the manipulator 1 can be managed by temporarily setting a temporary control target or making swinging operations executed by the total evaluation section 20.
Thus, according to the manipulator control method of the first embodiment, position control can be carried out in a state of robustness against the ambient environments or joint failures, so that the position control can be achieved with ease even if redundancy or nonlinear drive elements are involved.
Further, the control method of the first embodiment, which uses the same control rules even with the manipulator changed in configuration or joint count, is enabled to manage such changes in configuration or joint count only by changing configurational parameters of the manipulator.
The present invention is not limited to the foregoing first embodiment, and may be embodied in other various modes. A manipulator control method according to a second embodiment of the invention is described below.
In actual scenes of use of the manipulator, there is a need for flexible management of various working operations. For this purpose, although the configuration or joint count of the manipulator may be changed depending on the working operation, yet the control method of this second embodiment can be exploited in order to eliminate the need for preparing programs or rewriting programs in accordance with the configuration or joint count of the manipulator. As a result of this, even changes in the configuration or joint count of the manipulator can be managed only by parameter changes, allowing the manipulator to be added and changed to a robot or the like for immediate use in a plug-and-play like fashion.
Hereinbelow, a method for achieving addition and changes of the manipulator in plug and play is described with reference to the accompanying drawings.
Referring to
The total evaluation section 120 comprises an evaluation computation device 131, a communication device 132, a storage device 133 for storing therein, as data, such joint information as identification information and morphological information concerning each of the joint axes 3-9 included in the manipulator 101 under the current control, a monitoring device 134 for monitoring changes in connection states of the joint axes 3-9 constituting the manipulator 101 based on the data stored in the storage device 133, and a joint information updating device 135 for, upon detection of a change in the connection states by the monitoring device 134, updating the data stored in the storage device 133 into changed joint information.
Since the joint control sections 123-129 have a similar construction, construction of the joint control section 123 as a representative is described below. The joint control section 123 includes a measuring device 3s, a control computation processing device 3c, an actuator 3a, a communication device 31, and a storage device 50 for storing therein such joint information as identification information and morphological information as to the joint of the joint control section's own.
In this case, the joint axis identification information stored in the storage device 50 of the joint control section 123 is, desirably, identification information unique from joint axis to joint axis as an example. Then, adding this identification information to communication data transmitted by the communication device makes it possible to discriminate whether or not communication data has been derived from the joint axis. In addition to this, the identification information can be specified as an address of commands from the total evaluation section 120 to the joint axes 3-9, so that the respective joint control sections 123-129 can exert control for their own joints only when identification information coincides with those joints' own identification information.
The communication device 132 of the total evaluation section 120 and the communication device 31 of the joint control section 123 are connected to each other via a network 51. The network 51 may be, for example, a network connected to the joint control sections 123-129 in the same order as the connection in the manipulator 101, which starts from the total evaluation section 120 and terminates by the joint axis 9 located at the forward end of the manipulator 101. With such a connection, the connection states of the individual joint axes 3-9 can be easily grasped by using the routing of the network 51. It is noted that the connecting method of the network 51 is not limited to such a method, and other methods may be used. In such a case, for example, detecting a connection state between adjoining joint axes and putting the connection state onto the network 51 as data allows the connection states of the individual joint axes to be grasped.
Identification data and connection states detected in this way are normally monitored through a comparison with the joint information concerning the manipulator 101 stored in the storage device 133 by the monitoring device 134 in the total evaluation section 120, where a difference, if any, is detected as a change in the connection states. Also, the joint information stored in the storage device 133 is updated by the joint information updating device 135 with use of joint information collected from the joint axes 3-9.
Next, a method for changing a component element of the manipulator 101 by plug and play is described with reference to the schematic views of the manipulator 101 shown in
First,
Referring to
Referring to
Referring to
Referring to
Referring to
According to the manipulator control method described above, control is carried out on unified control rules regardless of the configuration and joint count of the manipulator, while parameters can be updated by autonomous detection of the construction of the manipulator. Therefore, even when the manipulator is subjected to a change of its component elements, control can be carried out in a plug-and-play fashion, i.e., continuously and safely. Thus, the manipulator can be easily changed in its configuration and joint count depending on working operation, hence its flexible and simple adaptability to a wider variety of operations.
Next, a control method by a manipulator control system according to a third embodiment of the invention is described with reference to a schematic view of the manipulator control system shown in
As shown in
Each of the joint control sections 223-229 includes a measuring device (9s etc.) having an encoder or other sensor mounted on each of the joint axes 3-9, an actuator (9a etc.) for driving its corresponding joint axis, and a control computation processing device (9c etc.) for calculating a control command value for the actuator based on input information. The total evaluation section 220 includes a total evaluation processing device 221.
The control method for the manipulator 201 in this third embodiment is a method in which under the exertion of position control for moving the hand 18 of the manipulator 201 toward the control target 19, force control is performed so as to hold a constant contact force applied from the hand 18 to a working object 209. In order to fulfill such force control, the hand 18 is equipped with a force measuring device 222 for measuring contact force.
As shown in
In each of the joint control sections 223-229, at step S17, based on the joint-displacement and joint-velocity information as to the joint control section's own joint, as well as on the transmitted evaluation result and the manipulator total-state information, a control command value for the joint control section's own actuator is calculated independently of the other joint axes (third step). Subsequently, at step S18, based on the calculated control command value, the actuator of the relevant joint is driven. Control processes of these steps S11-S18 are iteratively executed. At step S15, if it is decided from the evaluation result that the hand 18 of the manipulator 201 has reached the control target (target position and target contact force), the position control and force control for the manipulator 201 is completed. It is noted that the control processes of steps S11, S17 and S18 are executed independently of one another by their corresponding joint control sections 223-229, respectively, while the control processes of steps S12-S16 are executed by the total evaluation section 120.
Referring to
Concrete values, evaluation results and the control computation method to be computed in the individual processing steps in the control method of the third embodiment are set as follows as an example. First, in the control processing flow of
Position of the hand 18 of the manipulator 201 can be determined by substituting joint displacements of all the joint axes 3-9 into Equation (1).
Further, substituting measured joint velocities of the joint axes 3-9 into Equation (3) allows the velocity of the hand 18 to be calculated and the Jacobian matrix as well to be calculated simultaneously.
Further, an evaluation result computed in the step S14 of the total evaluation section 220 is computed as shown in
Dp=G−H (9)
Next, a contact force difference between a contact force Ft of the control target and an actual contact force Fr, i.e. a positional deviation equivalent to the force difference, is calculated. A resultant force-equivalent deviation vector Df can be expressed as shown in Equation (10). It is noted that Kf represents a control gain, for which an appropriate value is selected by the system.
Df=Kf(Ft−Fr) (10)
By using the position deviation vector Dp and the force-equivalent deviation vector Df represented by above Equations (9) and (10), respectively, a total deviation vector D to be used for control evaluation is calculated as shown by Equation (11):
D=Dp+Df (11)
After the calculation of the total deviation vector D by Equation (11) as shown above, by a procedure similar to that of the position control method of the first embodiment, motion vectors of the hand 18 in three cases, i.e. a case of maintaining the current velocities of the joint axes 3-9 (V), a case of acceleration (V+αn), and a case of deceleration (V−αn), as well as magnitudes C of directional components of the respective deviation vectors, are calculated by using Equations (3), (5), (6), (7) and (8). With reference to results of the calculation, a joint velocity for each joint axis at which C becomes the largest, i.e. the velocity of the hand 18 becomes closest to the direction of the control target, is adopted as the control target.
With respect to this control target, control for the n-th joint is carried out, as shown by Equation (12), as such control that a torque (Tn+ΔTn), which is a result of adding ΔTn to a current output torque Tn, is outputted:
ΔTn=Mn·Δωn/Δt+Kdn·Δωn (12)
where Δn represents a velocity difference between the selected control target of joint velocity for the n-th joint and the current joint velocity, and Δt represents a control unit time. It is assumed that Mn is a moment of inertia of the n-th joint and Kdn is a viscosity resistance component of the n-th joint. Using the control torque output (Tn+ΔTn) calculated in this way makes it possible to calculate such a control command value of the joint velocity for the n-th joint that the arrival of the hand 18 at the target position as well as the generation of the target contact force can be achieved more effectively.
According to the manipulator control method exemplified by the above-described solutions, even when one joint axis is disabled from motion due to effects of the ambient environments or joint failures, the redundancy is naturally exerted by the other joints being independently directed toward the control target. Therefore, the position control and force control can be carried out while the robustness is held against ambient environments and joint failures. Thus, there can be provided a control method and a control system for the manipulator capable of, even with redundancy and nonlinear drive elements involved, easily and flexibly achieving the control independently of uncertainties of the ambient environments, joint failures and the like.
This third embodiment has been described on a case where position control and force control for the hand of the manipulator 201 are performed in combination, as an example. However, instead of such a case, the control method of the third embodiment can be considered applicable also to cases where only the force control is performed.
The foregoing embodiments have been described on a case where the manipulator 1 or the like is controlled for its operation under the state that the base 2 for supporting the arm portion of the manipulator 1 or the like is fixed at one position. However, the present invention is not limited to such cases only, and the invention allows adoption of, for example, such a construction as shown in the schematic view of
It is to be noted that, by properly combining the arbitrary embodiments of the aforementioned various embodiments, the effects possessed by them can be produced.
Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.
The entire disclosure of Japanese Patent Application No. 2006-082269 filed on Mar. 24, 2006, including specification, drawings, and claims are incorporated herein by reference in its entirety.
According to the control method and the control system for manipulators in the present invention, there can be realized position control having a robustness and capable of achieving the control even with uncertainties and variations of the ambient environments or joint failures or the like. Since the control method and the control system are capable of easily and flexibly achieving the position control by using less numbers of sensors even with redundancy or nonlinear drive elements involved, those control method and control system can be applied to industrial- and consumer-use robot arms or the like dedicated to working operations being more complex and requiring higher degrees of freedom. In particular, those control method and control system are useful for applications to household robots which involve the presence of many obstacles as well as many environments in which their locations are indeterminate.
Number | Date | Country | Kind |
---|---|---|---|
2006-082269 | Mar 2006 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/JP2007/056023 | 3/23/2007 | WO | 00 | 12/21/2007 |