A Method for Compensating the End-Position Error of a Cable-Driven Continuum Manipulator

Abstract

The present disclosure discloses a method for compensating the end position error of a cable-driven continuum manipulator, including: selecting the first joint bending angle β1 and the second joint bending angle β2 of the continuum manipulator; calculating the lengths l of the driving cables in the continuum manipulator according to β1 and β2 i ; obtaining the actual end position of the continuum manipulator; calculating the error between the actual end position and the theoretical end position of the continuum manipulator; determining whether the error is within an acceptable range, if it is within the acceptable range, no error compensation is required; otherwise, proceed to the next step; determining the deviation direction of the error and selecting different correction methods for correction to obtain the corrected joint bending angles; calculating the lengths l of the driving cables in the continuum manipulator according to the corrected joint bending angles y ; taking the lengths l of the driving cables y and subtracting the lengths l of the driving cables i to obtain the length change amounts of the driving cables. If the length change amounts are within the acceptable range, the compensation ends; otherwise, the theoretical joint bending angles are reselected.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of robotics, and particularly relates to a method for compensating the end position error of a cable-driven continuum manipulator. Background Art

[0002] Due to its unique flexibility, the continuum manipulator can flexibly change its own shape to adapt to restricted and unstructured spaces, which has attracted wide attention in the medical and engineering fields. However, due to the difficulty of accurately evaluating its own flexible deformation through a theoretical model, the motion accuracy of the continuum manipulator is relatively low. However, while enjoying the superior performance brought by its flexibility, it also poses challenges to its own accurate motion modeling.

[0003] Different from traditional rigid-link robots that can directly perform motion modeling based on the D-H method, the continuum manipulator has no clear rotational joints due to its own flexibility. Therefore, its motion modeling is usually based on some assumptions, such as the piecewise constant curvature assumption, which is widely used. However, the kinematic modeling based on the piecewise constant curvature assumption often ignores its mechanical characteristics, such as gravity, friction, etc., which often leads to low modeling accuracy and difficulty in accurately evaluating the actual position and attitude of the continuum manipulator. Although some dynamic and static kinematic models or static and dynamic models considering mechanical factors can improve the accuracy of motion modeling to a certain extent, the complex iterative process and heavy computational amount of these methods pose great challenges to the real-time feedback compensation of the continuum manipulator. In fact, no matter how accurate the motion model is, there are still some errors caused by factors such as transmission and joint flexibility. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, the purpose of the present disclosure is to provide a method for compensating the end position error of a cable-driven continuum manipulator. This method compensates the motion error of the continuum manipulator through a visual feedback method, reconstructs the arm shape of the continuum manipulator through an adaptive visual detection method, and continuously compensates the end position error through a kinematic iterative correction method, and loops in this way until the error is within the range.

[0005] To achieve the above object, the present disclosure provides the following technical solutions:

[0006] A method for compensating the end position error of a cable-driven continuum manipulator, comprising the following steps:

[0007] S100: Select the first joint bending angle β1 and the second joint bending angle β2 of the continuum manipulator;

[0008] S200: Calculate the lengths l of the drive cables in the continuum manipulator according to β1 and β2 i ;

[0009] S300: Obtain the actual end position of the continuum manipulator;

[0010] S400: Calculate the error between the actual end position and the theoretical end position of the continuum manipulator;

[0011] S500: Determine whether the error is within an acceptable range. If it is within the acceptable range, no error compensation is required; otherwise, proceed to step S600;

[0012] S600: Determine the deviation direction of the error, and select different correction methods according to the deviation direction to correct the deviation, so as to obtain the corrected first joint bending angle β′1 and second joint bending angle β′2;

[0013] S700: Calculate the length l of each drive cable in the continuum manipulator according to the corrected joint bending angle y ;

[0014] S800: Subtract the length l of each drive cable y from the length l of each drive cable in step S200 i to obtain the length change amount of each drive cable. If the length change amount is within an acceptable range, the compensation ends; otherwise, return to step S100 to reselect the theoretical joint bending angle.

[0015] Preferably, in step S200, the length l of each drive cable i is calculated by the following formula:

[0016]

[0017] where l1 represents the length change amount of cable 1, l2 represents the length change amount of cable 2, l3 represents the length change amount of cable 3, l4 represents the length change amount of cable 4, l0 represents the length of the flexible rod, r represents the radius of the pitch circle where the cable hole is located, and δ1 represents the angle between the cable hole and the ring coordinate system.

[0018] Preferably, in step S600, the correction methods include correction method one, correction method two, correction method three, and correction method four;

[0019] Among them,

[0020] Correction method one is expressed as:

[0021] β′1 = β1 + Δβ, β′2 = β2 + Δβ

[0022] Correction method two is expressed as:

[0023] β′1 = β1 + Δβ, β′2 = β2 - Δβ

[0024] Correction method three is expressed as:

[0025] β′1 = β1 - Δβ, β′2 = β2 + Δβ

[0026] The fourth correction method is expressed as:

[0027] β′1 = β1 - Δβ, β′2 = β2 - Δβ

[0028] Wherein, β1 represents the first theoretical joint bending angle, β2 represents the second theoretical joint bending angle, Δβ represents the correction value for adjusting β1 and β2, β′1 represents the corrected first theoretical joint bending angle, and β′2 represents the corrected second theoretical joint bending angle.

[0029] Preferably, the continuum manipulator includes a manipulator body.

[0030] Preferably, the manipulator body includes a metal ring member and a flexible rod.

[0031] Preferably, in step S300, the actual end position of the continuum manipulator is obtained through a vision detection system.

[0032] Compared with the prior art, the beneficial effects brought by the present disclosure are:

[0033] The method of the present disclosure can effectively improve the motion accuracy of the continuum robot. In addition, the end position error compensation method and system for vision detection of the cable-driven continuum robot proposed by the present disclosure can correct the end position error of the cable-driven continuum robot in real time, without the need to establish a complex dynamic and static kinematic model, nor the need for a complex iterative process, and has universality for correcting the end position error of the continuum robot. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flowchart of a method for compensating the end position error of a cable-driven continuum manipulator provided by an embodiment of the present disclosure;

[0035] Figure 2 is a schematic structural diagram of a continuum manipulator provided by another embodiment of the present disclosure;

[0036] Figure 3 is a schematic structural diagram of a vision detection system provided by another embodiment of the present disclosure;

[0037] Figure 4 is a schematic diagram for solving the cable length provided by another embodiment of the present disclosure;

[0038] Figure 5 is a schematic diagram of the verification result curve of the method provided by another embodiment of the present disclosure;

[0039] Figure 6It is a schematic diagram of the compensation direction provided by another embodiment of the present disclosure. Detailed implementation manners

[0040] The following will refer to the attached Figures 1 to 6 The specific embodiments of the present disclosure will be described in detail below. Although specific embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be completely conveyed to those skilled in the art.

[0041] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. The specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of components as the criterion for distinction. As mentioned throughout the specification and claims, "comprising" or "including" is an open-ended term and should be interpreted as "including but not limited to". The subsequent description in the specification is the preferred implementation manner for implementing the present disclosure, but the description is for the purpose of the general principle of the specification and is not used to limit the scope of the present disclosure. The protection scope of the present disclosure shall be determined by the scope defined by the appended claims.

[0042] For the convenience of understanding the embodiments of the present disclosure, the following will further explain with specific embodiments as examples in conjunction with the drawings, and each drawing does not constitute a limitation on the embodiments of the present disclosure.

[0043] In one embodiment, as Figure 1 shown, the present disclosure provides a method for compensating the end position error of a cable-driven continuum manipulator, including the following steps:

[0044] S100: Select the first theoretical joint bending angle β1 and the second theoretical joint bending angle β2 of the continuum manipulator;

[0045] As Figure 2 shown, the continuum manipulator includes a manipulator body 2, and the manipulator body 2 is placed on an L-shaped fixing plate 1, and specifically includes a plurality of continuum manipulator structural units. Each structural unit includes a metal ring 3, a flexible rod 5 and a set screw 4, and each metal ring is connected by a drive cable. The drive cable controls the continuum manipulator to achieve bending motion through length change. When the manipulator performs bending motion, a bending angle will be generated between each structural unit. The theoretical joint bending angles β1 and β2 in this step are artificially selected for the convenience of testing, usually set between 0 and 90°, with an interval of 10°, just as a given initial value.

[0046] Exemplarily, the first theoretical joint bending angle β1 and the second theoretical joint bending angle β2 are respectively selected as: β2 = 0.

[0047] S200: Calculate the lengths l of the respective drive cables in the continuum manipulator according to β1 and β2 i ;

[0048] Exemplarily, there are 4 drive cables provided in the continuum manipulator. Then, according to the joint bending angles β1 and β2, the lengths of the 4 drive cables are calculated to be respectively: -0.921864 mm, -0.921864 mm, 0.8325746 mm, 0.835746 mm (- indicates cable contraction, + indicates cable stretching).

[0049] S300: Obtain the actual end position of the continuum manipulator based on the vision detection system;

[0050] Exemplarily, the actual end position of the continuum manipulator obtained based on this vision detection system is: (109.19 mm, 81.49 mm).

[0051] S400: Calculate the error between the actual end position and the theoretical end position of the continuum manipulator;

[0052] In this step, due to the different lengths of the manipulator, the error values will also be different. Therefore, the error is generally expressed as the percentage of the actual offset distance / the total length of the manipulator, and generally within 2% of the total length. In this embodiment, the total length of the manipulator is 150 mm, and the theoretical and actual offset distances of the end of the manipulator are 2.02 mm. Therefore, the error percentage is 1.35%.

[0053] S500: Determine whether the error is within an acceptable range. If it is within the acceptable range, no error compensation is required; otherwise, go to step S600;

[0054] In this step, due to the different lengths of the manipulator, the error values will also be different. Therefore, the error is generally expressed as the percentage of the actual offset distance / the total length of the manipulator, and generally within 2% of the total length. Exemplarily, if the total length of the manipulator is 150 mm and the theoretical and actual offset distances of the end of the manipulator are 2.02 mm, then the error percentage is 1.35%.

[0055] S600: Determine the deviation direction of the error, select different correction methods according to the deviation direction to correct the deviation, and obtain the corrected joint bending angle;

[0056] In this step, assuming that the theoretical end position is the origin of the plane rectangular coordinate system, the actual end position will fall on the four quadrants of the plane rectangular coordinate system, and each quadrant corresponds to a correction method.

[0057] S700: Calculate the length l of each drive cable in the continuum manipulator according to the corrected joint bending angle y ;

[0058] S800: Subtract the length l of each drive cable y from the length l of each drive cable in step S200 i to obtain the length change Δl of each drive cable;

[0059] In another embodiment, in step S600, as Figure 6 shown, the correction methods include correction method one, correction method two, correction method three, and correction method four. Specifically, when the actual end position falls in the third quadrant of the plane rectangular coordinate system, correction method one is adopted, and correction method one is expressed as:

[0060] β′1 = β1 + Δβ, β′2 = β2 + Δβ

[0061] When the actual end position falls in the fourth quadrant of the plane rectangular coordinate system, correction method two is adopted, and correction method two is expressed as:

[0062] β′1 = β1 + Δβ, β′2 = β2 - Δβ

[0063] When the actual end position falls in the first quadrant of the plane rectangular coordinate system, correction method three is adopted, and correction method three is expressed as:

[0064] β′1 = β1 - Δβ, β′2 = β2 + Δβ

[0065] When the actual end position falls in the second quadrant of the plane rectangular coordinate system, correction method four is adopted, and correction method four is expressed as:

[0066] β′1 = β1 - Δβ, β′2 = β2 - Δβ

[0067] Wherein, β1 represents the first theoretical joint bending angle, β2 represents the second theoretical joint bending angle, Δβ represents the correction value for adjusting β1 and β2, β′1 represents the corrected first theoretical joint bending angle, and β′2 represents the corrected second theoretical joint bending angle.

[0068] In another embodiment, in step S200, as Figure 4 shown, taking a structural unit of a continuum manipulator as an example, the structural unit includes three metal rings 16 (metal rings A, B, and C respectively), two pairs of flexible rods 17, and corresponding set screws 18. The three metal rings are controlled by four cables, and the relationship between the cable length and the joint bending angles β1 and β2 is:

[0069]

[0070] Among them, l1 represents the change in the length of cable 1, l2 represents the change in the length of cable 2, l3 represents the change in the length of cable 3, l4 represents the change in the length of cable 4, l0 represents the length of the flexible rod, r represents the radius of the pitch circle where the cable hole is located, and δ1 represents the angle between the cable hole and the ring coordinate system.

[0071] In this embodiment, if the single-segment continuum manipulator includes n structural units, the lengths of the four cables of the single-segment continuum manipulator are n times the lengths of the four cables of the structural unit.

[0072] Next, taking the single-segment continuum manipulator as an example, compare the motion results of the continuum manipulator during the 10° - 90° bending test before and after using the end position error compensation method. Obtain the arm shapes of both through the vision detection system and compare them with the theoretical results to evaluate the effectiveness of the method described in this disclosure. As Figure 5 shown, among them, the star-shaped solid line curve is the theoretical arm shape result, the square-shaped dashed line curve is the arm shape result without using the end position error compensation method, and the circular dotted line curve is the arm shape result using the method described in this disclosure. It can be seen from the comparison results that the method described in this disclosure can be closer to the theoretical arm shape result than without using the end position error compensation method. Specifically, when not using the end position error compensation method, the maximum end position error is:

[0073]

[0074] And after using the end position error compensation method, the maximum error is:

[0075]

[0076] That is, compared with not using the end position error compensation method, using the end position error compensation method improves the motion accuracy by 76.67%. Therefore, the effectiveness of the end position error compensation method proposed in this disclosure is proved.

[0077] In another embodiment, in step S300, the actual end position of the continuum manipulator is obtained through the vision detection system.

[0078] In this embodiment, as Figure 3 shown, the vision detection system includes an industrial camera 15, a triangular bracket 20, and a target detection algorithm. The triangular bracket 20 is used to fix the industrial camera 15, obtain the image information of the continuum manipulator through the industrial camera 15, and obtain and reconstruct the arm shape information of the continuum manipulator through the target detection algorithm for evaluating its motion performance.

[0079] The above general description of the invention involved in this application and the description of its specific embodiments should not be construed as limiting the technical solution of the invention. Those skilled in the art can, based on the disclosure of this application, without violating the constituent elements of the involved invention, add, subtract, or combine the disclosed technical features in the above general description or / and specific embodiments (including examples) to form other technical solutions that fall within the protection scope of this application.

Claims

1. A method for compensating the end - position error of a cable - driven continuum manipulator, comprising the following steps: S100: Select the first joint bending angle and the second joint bending angle of the continuum manipulator and the second joint bending angle ; S200: Calculate the lengths of the drive cables in the continuum manipulator according to and ; l i ; S300: Obtain the actual end - position of the continuum manipulator; S400: Calculate the error between the actual end - position and the theoretical end - position of the continuum manipulator; S5 00: Determine whether the error is within an acceptable range. If it is within the acceptable range, no error compensation is required; Otherwise, proceed to step S600; S6 00: Determine the deviation direction of the error, and select different correction methods according to the deviation direction to correct the deviation, so as to obtain the corrected first joint bending angle and the second joint bending angle ; S700: Calculate the lengths of the drive cables in the continuum manipulator according to the corrected joint bending angles l y ; S800: The lengths of the respective drive cables l y are subtracted from the lengths of the respective drive cables in step S200 l i to obtain the length change amount of each drive cable. If the length change amount is within an acceptable range, the compensation ends; otherwise, return to step S100 to reselect the theoretical joint bending angle. Among them, in S600, assuming that the theoretical end - position is the origin of the plane rectangular coordinate system, the actual end - position will fall on the four quadrants of the plane rectangular coordinate system, and each quadrant corresponds to a correction method. The correction methods include correction method one, correction method two, correction method three, and correction method four; When the actual end - position falls on the third quadrant of the plane rectangular coordinate system, correction method one is adopted. Correction method one is expressed as: ； When the actual end - position falls on the fourth quadrant of the plane rectangular coordinate system, correction method two is adopted. Correction method two is expressed as: ； When the actual end - position falls on the first quadrant of the plane rectangular coordinate system, correction method three is adopted. Correction method three is expressed as: ； When the actual end - position falls on the second quadrant of the plane rectangular coordinate system, correction method four is adopted. Correction method four is expressed as: ； Wherein, represents the first theoretical joint bending angle, and represents the second theoretical joint bending angle, represents a correction value for adjusting and , represents the corrected first theoretical joint bending angle, represents the corrected second theoretical joint bending angle.

2. The method according to claim 1, wherein, In step S200, the lengths of the respective drive cables l i are calculated by the following formula: ； Among them, l 1 represents the length change of cable 1, l 2 represents the length change of cable 2, l 3 represents the length change of cable 3, l 4 represents the length change of cable 4, l 0 represents the length of the flexible rod, and r represents the radius of the pitch circle where the cable hole is located, represents the angle between the cable hole and the ring coordinate system.

3. The method according to claim 1, wherein, The continuum manipulator includes a manipulator body.

4. The method according to claim 3, wherein, The manipulator body includes a metal - ring member and a flexible rod.

5. The method according to claim 1, wherein, In step S300, the actual end - position of the continuum manipulator is obtained through a vision detection system.

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