WO2014030363A1 - External force estimation device and forceps system - Google Patents

Description

External force estimation device and forceps system

The present invention relates to a novel external force estimation device. The present invention also relates to a novel forceps system having this external force estimation device.

A multi-degree-of-freedom forceps used in a conventional surgical robot system (for example, see Non-Patent Document 1) has a 2-degree-of-freedom arm inside the body (3 degrees-of-freedom when grasping is included) and a 4-degree-of-freedom arm outside the body. This is because it is difficult to realize multiple degrees of freedom at the tip of the small-diameter forceps.

However, in the forceps system of Non-Patent Document 1, the arm outside the body moves up and down, left and right, etc. during work, which interferes with the assistant, and when using a plurality of forceps, the arms interfere with each other. There is a point.

In addition, research aimed at increasing the degree of freedom using an elastic body has been carried out (see Non-Patent Documents 2 and 3).
Non-Patent Document 2 is an endoscope bending mechanism. Ring-shaped leaf springs are laminated together by welding to form a single spring structure. Bends close to 180 ° are possible.

Non-Patent Document 3 realizes bending in an arbitrary direction by connecting four leaf springs to a rigid rod.

The inventor has developed a laparoscopic forceps manipulator having a simple flexible bending mechanism suitable for miniaturization (see Non-Patent Document 4). The joint structure consists only of a single-work cutting spring. By bending and pushing the superelastic alloy wire that passes through the pneumatic cylinder, a bending operation with higher rigidity than the conventional antagonistic drive using wire tension. Made possible. The joint can bend in two degrees of freedom.

The present inventor performs external force estimation using a simple theoretical model that approximates a flexible joint to a rigid link mechanism with two degrees of freedom (see Non-Patent Document 5).

Hagn, U., et al .: DLR MiroSurge: a versatile system for research in endoscopic telesurgery, InternationalJournal of Computer Assisted Radiology and Surgery, Vol. 5, p.183-193 (2010), 10.1007 / s11548-009-0372 Four Breedveld, P., Hirose, S.:Development of the Endo-Periscope for improvementimpofdepth perception in laparoscopic surgery, ASME Design Engineering Technical ConferencesComputers and Information in Engineering Conference (2001) Arata, J., Saito, Y., Fujimoto, H .: Outer shell type 2 DOF bending manipulator using spring-link mechanism formedical applications, Robotics and Automation (ICRA), 2010 IEEE InternationalConference on, p. 1041-1046 (2010) Daisuke Haraguchi, Kotaro Kanno, Kengo Kawashima: Development of pneumatic drive forceps manipulator using push-pull mechanism of superelastic alloy wire, 12th Symposium on Fluid Measurement and Control, Proc. 22-25 Daisuke Haraguchi, Kotaro Tadano, Kenji Kawashima: A Prototype of Pneumatically-Driven Forceps Manipulator withForce Sensing Capability Using a Simple Flexible Joint, 2011 IEEE / RSJInternational Conference on Intelligent Robots and 931-936

Also, the bending mechanism of Non-Patent Document 2 cannot bend isotropically in all directions due to structural limitations. In Non-Patent Document 3, there is a concern that a small part such as a shaft is required for connection, and that it is weak against torsion. In addition, Non-Patent Document 2 and Non-Patent Document 3 have problems such as a large number of parts and time-consuming assembly.

In the joint structure of Non-Patent Document 4, the external force estimation method is not described.
The external force estimation based on the theoretical model of Non-Patent Document 5 is effective when the joint is in a straight posture, but the error increases as the bending angle increases. In addition, there is no description about force estimation with 3 degrees of freedom.

Therefore, development of a new external force estimation device and forceps system that solves such problems is desired.
This invention is made | formed in view of such a subject, and it aims at providing a novel external force estimation apparatus.
Moreover, an object of this invention is to provide the novel forceps system which has this external force estimation apparatus.

In order to solve the above-described problems and achieve the object of the present invention, an external force estimation device of the present invention includes a detection unit that detects a change amount of the length of the elastic member, and a change amount of the elastic member that is deformed by an external force. And a calculation unit for calculating external force.

Here, although not limited, it is preferable that the calculation unit calculates the three-axis component of the external force. Although not limited, it is preferable to use a wire for detecting the amount of change. Moreover, although not necessarily limited, it is preferable that a detection part consists of a position sensor. Moreover, although not necessarily limited, it is preferable to detect the change amount of the joint having elasticity.

The forceps system of the present invention has the external force estimation device.

The present invention has the following effects.

The external force estimation device of the present invention has a detection unit that detects a change amount of the length of the elastic member and a calculation unit that calculates the external force using the change amount for the elastic member that is deformed by the external force. An estimation device can be provided.

Since the forceps system of the present invention has the external force estimation device, a novel forceps system can be provided.

It is a figure which shows the structure of the whole system. It is a schematic diagram of the drive system about 1 degree-of-freedom bending. It is a figure which shows the external appearance of a forceps manipulator. It is a figure which shows the front-end | tip part of a forceps manipulator. It is a figure which shows the drive part of a forceps manipulator. It is a figure which shows the pipe internal structure of a forceps manipulator. It is a figure which shows the cross section of the pipe part of a forceps manipulator. It is a block diagram of external force estimation. It is a figure which shows the definition of a position coordinate. It is a figure which shows an experimental apparatus. It is the figure which compared the external force estimated value when it always calculated as l = 0, and the measured value of a force sensor. It is the figure which compared the 3 DOF external force estimated value and the measured value of a force sensor.

Hereinafter, the form for carrying out the invention concerning an external force estimating device and a forceps system is explained.
The external force estimation apparatus of the present invention is an apparatus having a detection unit that detects a change amount of the length of the elastic member and a calculation unit that calculates an external force using the change amount for an elastic member that is deformed by an external force.
The forceps system of the present invention is a system having the external force estimation device.

In the text of this specification, “(English character symbol) hat” refers to an English character symbol with a hat symbol, and “(English character symbol) over dot” refers to an English character symbol with an over dot. It describes.

The configuration of the entire system will be described with reference to FIG. This is a system that takes the cylinder position signal from a position sensor (potentiometer, encoder, etc.) and the pressure signal at the output port of the servo valve into a control computer having a calculation unit, and calculates and outputs the input voltage to the servo valve. . By disposing a pressure sensor for measuring the driving force of the cylinder on the control system side, the driving force can be estimated without mounting a force sensor on the manipulator side.

Next, a drive system with one-degree-of-freedom bending will be described with reference to FIG. Bending in one direction is realized by two cylinders. Here, for simplicity of explanation, a schematic diagram of one-way bending is shown, but a total of four cylinders are used for bending in two directions. Each cylinder is driven by one 5-port servo valve. Symbol suffixes 1 and 3 of each drive channel correspond to the wire arrangement numbers in FIG. A pressure sensor is attached to the output port of the servo valve, and the driving force of the cylinder can be estimated from the pressure measured here. A potentiometer is attached to the cylinder rod as a position sensor.

Next, a forceps manipulator constituting the forceps system will be described.
FIG. 3 shows the appearance of the forceps manipulator.

Next, each part which comprises a forceps manipulator is demonstrated.
FIG. 4 shows the tip of the forceps manipulator. The distal end portion is composed of a bent portion (joint) and a grip portion. The joint part employs a precision spring manufactured by cutting, and the attachment part with the gripping part and the guide hole of the drive wire can be integrally processed. There are four drive wire through holes in the spring wall, and super elastic alloy wires are passed through them and fixed at the end of the spring. By combining the pushing and pulling of the four superelastic alloy wires, a bending operation in an arbitrary direction and an expansion / contraction operation in the longitudinal direction are possible. The gripping part is a mechanism that opens and closes by air pressure. For this reason, an air pipe is passed through the joint. Since the grip portion is not wire-driven, there is an advantage that the opening / closing operation does not interfere with the bending operation of the joint.

FIG. 5 shows the drive unit of the forceps manipulator. Four superelastic alloy wires that drive the joint are connected in a straight line to the rod of the pneumatic cylinder through the connector. Since the wire is not bent during the connection process, that is, the wire is always in a straight line except for the bending joint, the sliding frictional force of the mechanism during driving can be minimized, contributing to improvements in controllability and external force estimation accuracy. To do. The cylinder rod position is measured with a potentiometer. By controlling the rod position of the pneumatic cylinder, the superelastic alloy wire is pushed and pulled to cause the tip joint to perform a desired motion.

FIG. 6 shows the internal structure of the body pipe part of the forceps manipulator. FIG. 7 shows a cross-sectional view of the pipe portion. As shown in FIG. 7, the superelastic alloy wire passes through the guide pipe and is connected to the bending joint to prevent buckling. As shown in FIG. 6, the guide pipe itself is also passed through the support member at regular intervals to prevent buckling.

Next, external force estimation in the forceps system will be described.
FIG. 8 is a block diagram of external force estimation in the forceps system.

With respect to the block diagram of FIG. 8, a method of external force estimation will be described while explaining each symbol.
F: Driving force vector of the pneumatic actuator, specifically, a force vector for pushing and pulling the cylinder rod.
X: The displacement of the cylinder rod, calculated from the value of the potentiometer.
X overdot: The speed of the cylinder rod. Although s is a Laplace differential operator, it is actually obtained by computer numerical differentiation (pseudo-differentiation).
Note that the above three variables relate to the pneumatic cylinder and are four-dimensional vectors.
q: A position variable vector of the flexion joint, which is a three-dimensional vector represented by Expression (2). The specific meaning of each component of q is shown in FIG.

That is, the direction δ in which the joint bends, the angle θ bent in that direction, and the amount of change l in the joint length. The change amount l of the joint length is the change amount of the length of the center line of the joint, that is, the portion indicated by the broken line in FIG. However, δ and θ are expressed in the following ranges.
−π ≦ δ ≦ π θ ≧ 0
P is the position coordinate of the forceps tip, Ls is the natural length of the flexion joint, Lg is the length of the gripping part, r is the arrangement radius of the drive wire, and numerals 1 to 4 are the drive wires. Number.

Suppose that the joint bends into an ideal arc, and the relationship with the cylinder rod displacement X described above is as follows.

　また、鉗子先端の位置Pは次のように表わせる。

The position P of the forceps tip can be expressed as follows.

Z hat: Inverse dynamic model of joints, which is a cylinder driving force vector for realizing a desired joint position and velocity, and is a four-dimensional vector. The Z hat is calculated as follows.

The first term is the cylinder viscosity, and C is the viscosity matrix.
The second term is the Coulomb friction of the whole mechanism, and D is a matrix of Coulomb friction force. μ is a dynamic friction coefficient. Since this frictional force increases when the joint is bent, it is a nonlinear function of the bending angle θ. The nonlinear part e 2 ^μθ in the second term is not limited to the above. An approximate polynomial of θ identified experimentally can also be applied.

In Non-Patent Document 5, there is no nonlinear part related to θ, but the above two terms are a more accurate friction model according to the bending state of the joint. If the second term is used, the frictional force can be estimated more accurately than the equation described in Non-Patent Document 5. As a specific effect of this, accuracy in manipulator position control and external force estimation is improved.

The third term is the elastic force applied to the bending of the joint, and K _b is its stiffness matrix. The third term is a model that linearly approximates the elastic force for bending. A similar expression is described in Non-Patent Document 5, but there is a difference in the joint structure applied in this application and Non-Patent Document 5. In Non-Patent Document 5, a superelastic alloy spine is provided at the center of a flexible joint, and a stainless steel wire having almost no elastic force is used as a drive wire. In the present invention, there is no spine at the center of the joint, and a superelastic alloy having elasticity is used for the drive wire.

Fourth term in the elastic force exerted on the expansion and contraction of the joint, K _a is the stiffness matrix.
In the present invention, in Expressions (1) to (4), in addition to variables δ and θ representing joint flexion, a variable l representing expansion and contraction is introduced as a variable of the third degree of freedom, so that three independent degrees of freedom (3 Axis) external force can be estimated.
It should be noted that the influence of inertia including gravity is assumed to be sufficiently smaller than the above components and can be ignored.

F _ext , F _ext hat: vectors of external force components of cylinder driving force, which are four-dimensional vectors. This occurs when the cylinder is back-driven by receiving external force at the tip of the forceps. A symbol with a hat means an estimated value by calculation. The same applies to symbols to be described later.
τ _ext hat: an external force component of torque and translational force with respect to joint position coordinates q (δ, θ, l).
f _ext hat: An external force vector applied to the forceps tip, which is a three-dimensional vector in the x, y, and z directions.
J _a ^T is a conversion matrix from F _ext to τ _ext . J _a is a Jacobian from the joint speed q overdot to the cylinder speed X overdot, and can be calculated by differentiating the equation (1) with respect to time.
(J ^T ) ⁺ : A conversion matrix from τ _ext to f _ext . J is a Jacobian from the joint speed q overdot to the forceps tip speed p overdot, and can be calculated by differentiating the equation (3) with time.

Explain the principle of external force estimation. By subtracting the internal reverse dynamics Z hat of the manipulator from the driving force F of the cylinder, the component applied to the external force can be obtained. Ie

This can be converted by the conversion matrix of each level described above, and an external force acting on the tip can be obtained. Ie

　式(6)の各行列中に、関節長さの変数lにかかる成分が存在するため、独立した3軸の並進力を推定することができる。

In each matrix of Equation (6), there is a component related to the joint length variable l, so that independent three-axis translational forces can be estimated.

Next, an example of a bending forceps system will be described. For the examples, the experimental conditions will be described.
The following values were used for Lg and joint Ls, r.
Lg = 30mm
Ls = 20mm
r = 3.6mm

The values of C, D, μ, Kb, Ka were obtained experimentally. That is, automatic control was performed by giving an appropriate trajectory to the flexion joint, and the above parameters were adjusted by trial and error so that the target trajectory and the actual trajectory were in good agreement.
The following values were used for C, D, μ, Kb, and Ka.
C = 0.3 [N ・ s / mm]
D = 0.6 [N]
μ = 0.9
Kb = 2.8 [N / mm]
Ka = 2.0 [N / mm]

The experimental method will be described for the examples. As shown in FIG. 10, the tip of the forceps is bent about 30 degrees, and the gripping part and the force sensor are connected with a wire. In this state, the wire was pulled by moving the entire forceps in the direction of the arrow in the figure. At this time, the effectiveness of the external force estimation described above was verified by comparing the estimated value of the external force by the forceps manipulator and the measured value of the force sensor.

In this example, the external force was finally calculated using Equation (6). The matrix and vector components in Equation (6) were calculated using the previous equations. Also in the comparative example with respect to the example, the external force was finally calculated using the equation (6). However, the equations (1) to (4) in the calculation process were calculated by setting all l to 0.

The experimental results will be described. Regarding the external force acting on the forceps tip in this experiment, the force component in the joint expansion / contraction direction accounts for a large proportion.
In the comparative example, only the force component in the biaxial direction perpendicular to the bending direction can be detected, that is, the force acting in the expansion / contraction direction of the joint cannot be detected. As shown, the sensitivity of external force estimation is significantly reduced.

On the other hand, in the method of the present invention, as shown in FIG. 12, it can be confirmed that the force of the three-axis component can be estimated well using only the bending joint at the tip.

From the above, the external force estimation device and forceps system of the present invention have the following effects.
By significantly reducing the number of components of the bending joint at the tip, manufacturing force can be reduced, and it becomes easy to manufacture a small forceps having an outer diameter of 5 mm or less.

Also, the combination of cutting spring and superelastic alloy wire can increase the rigidity required for work while being a flexible body.

Also, translational external force with 3 independent degrees of freedom (3 axes) can be estimated using only the joint at the tip. The ability to estimate an independent triaxial translational force (xyz) means that the force can be felt in any translational direction. An advantage of using the joint at the tip for estimating the external force is that it is not affected by the restraint of the movement from the trocar and the frictional force that pass when inserting into the abdominal cavity. That is, the external force estimation accuracy is unlikely to deteriorate due to factors such as differences in the forceps insertion state in each operation.

Although an example of a spring as an elastic member has been described, the elastic member is not limited to this. In addition, as the elastic member, it is possible to employ a member that is formed by processing a slit in a hollow object so that it can be flexibly bent.

∙ When the number of wires to be driven is one, external force estimation with one degree of freedom can be performed, and when two wires are driven, external force estimation with two degrees of freedom can be performed. In order to estimate the external force with three degrees of freedom in the present invention, at least three drive wires are required. The advantage of using four drive wires is that the structural symmetry improves the independence of the degree of freedom in bending and simplifies the calculation formula.

Although an example of a superelastic alloy wire has been described as a member that transmits the change amount of the length of the elastic member, the member that transmits the change amount is not limited to this. In addition, as a member for transmitting the amount of change, a flexible wire made of another material such as a stainless steel wire can be employed.

Although an example of a potentiometer as a cylinder position detection unit has been described, the detection unit is not limited to this. In addition, an encoder or the like can be employed as the detection unit.

Although an example of an air cylinder has been described as the driving force generator, the driving force generator is not limited to this. In addition, an electric motor, a hydraulic cylinder, a hydraulic cylinder, or the like can be employed as the driving force generator.

Although an example of a pressure sensor has been described as a driving force measuring device, the driving force measuring device is not limited to this. In addition, as a driving force measuring device, a method of directly mounting a force sensor on a manipulator can be employed.

Although an example of a forceps system has been described as an application of the external force estimation device, the application of the external force estimation device is not limited to this. Other applications of the external force estimation device include application to a manipulator that cannot be equipped with a force sensor because it is used in an electromagnetic environment.

Claims (6)

For an elastic member that is deformed by an external force, a detection unit that detects a change in the length of the elastic member;
An external force estimation device having a calculation unit that calculates an external force using the amount of change. The external force estimation device according to claim 1, wherein the calculation unit calculates a triaxial component of the external force. The external force estimation apparatus according to claim 2, wherein the change amount is detected using a wire. The external force estimation apparatus according to claim 3, wherein the detection unit includes a position sensor. The external force estimation apparatus according to claim 4, wherein a change amount of a joint having elasticity is detected. A forceps system comprising the external force estimation device according to any one of claims 1 to 5.

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