源到位精度是近距离放射治疗后装机的重要性能指标之一,多种因素可导致源到位误差,影响放射剂量准确度.从理论和实验角度探究了多种因素对源到位精度的影响.首先,基于后装机传动特点,建立了源缆一导管静力学模型,分析源缆输入和输出力比值随摩擦因数和治疗导管弯曲形状变化关系.然后建立源缆传输动力学模型,分析了柔性源缆进给过程中弹性变形量与源缆长度和导管弯曲半径的关系.最后设计制造出测试平台,实验探究多种因素对源到位精度的影响,间接证明了理论分析的正确性.

This article mainly includes the developing, dynamical modeling and control of a tendon-based robot system. First, a 5-degree-of-freedom tendon-based magnetic resonance imaging–compatible robot for prostate needle insertion surgery is introduced briefly. What follows is the dynamical modeling of the robot system, where a mechanical dynamic model is established using the Lagrange method, and a lumped parameter tendon model is used to identify the nonlinear gain of the actuator. Based on the dynamical model, a fuzzy sliding mode control algorithm is proposed for accurate position control of the robot. Through simulations using different sinusoidal input signals, we observed that the sinusoidal tracking error at 1/2π Hz is 0.2 mm and the needle tip positional precision of tracking a spatial arched curve remains less than 0.3 mm. Finally, experiments on tendon-sheath transmission and robot position tracking are conducted, which shows that the insertion precision is 0.67 mm in laboratory environment.

Tendon-based transmission has significant advantages in the development of a surgical robot, which is fully magnetic resonance imaging compatible and can work dexterously in the very limited space inside magnetic resonance imaging core. According to the requirements of magnetic resonance imaging compatibility, a novel 6 degrees of freedom tendon-based surgical robot composed of three independent modules is developed in this paper. After a brief introduction to the robot, the direct and inverse kinematic equations are deduced by applying the concept of screw displacements, and the reachable workspace of the robot is calculated. As to the static force analysis, we apply the principle of virtual work to derive a transmission between the equivalent joint torques and the tendon forces. By the use of the pseudoinverse technique, a systematic method is developed for the resolution of redundant tendon forces.

In this paper, a high precision tendon-based magnetic resonance imaging-compatible robot for prostate needle-insertion surgery is introduced briefly, which is possessed of five degrees of freedom. What follows is the kinematic analysis together with the Jacobian analysis. Based on the forward kinematics, the reachable workspace of the robot is then calculated. The main contribution of this paper, an error model of the robot considering the input errors, form and position errors of the revolute joints, and main parts of the manipulator is then established. To obtain the backlash associated with the tendon-based transmission system, the statics analysis is conducted. Given a series of certain values of the error source mentioned above and a certain trajectory of the surgical needle tip, which is based on kinematics in the reachable workspace, the comparative result of the trajectory based on the error model is obtained. Finally, the experiment is conducted to verify the veracity of the error model.

In this paper, we focus on the design requirement of a high-precision magnetic resonance imaging-compatible robot for prostate needle-insertion surgery, which is actuated by five ultrasonic motors to achieve the goal of needle posture adjustment and prostate puncture. After a brief introduction to the robot, the direct and inverse kinematic equations are deduced. In order to show the relationship of the velocity between the actuators and the end effector, the Jacobian matrix is derived by formulating a velocity closed-loop equation for each limb. The kinematics is carried out by minimizing a global and comprehensive dimensional synthesis conditioning index subject to transmission angle and range of motion of the mechanism constraints. The dimensional parameters are obtained for achieving a good kinematic performance throughout the entire task workspace by an example, and finally the reachable workspace of the robot is calculated.

In recent years image guidance technology and robot assisted surgical technique have become an active research area. In order to guarantee the safety of operation, robot needs to meet more stringent reliability. Since MRI-guided surgical robot research is still in its infancy, the research in this field has become an urgent task. This paper introduces the reliability analysis method of an MRI-guided robot system for brachytherapy. For the surgical robot which works in the strong magnetic field, the reliability includes: MR-compatibility, mechanism precision, control precision and safety. Firstly, MR-compatibility involves compact structure, non-ferromagnetic materials and MR-compatibility of power source and transducer. Secondly, mechanism and control precision are analyzed. The influence factor analysis of mechanism precision is performed, while hybrid control method which integrated pneumatic control and ultrasonic motor control is applied. Finally, safety has been presented, which include modular design, sterilization ability and emergency response, optimized needle installation component. In addition, the MR-compatible SNR test and physical space validation are conducted to prove the MRI-compatibility in hospital. Precision experiment based on the visual acquisition system is also carried out in the laboratory to ensure the reliability of system. © 2013 Springer-Verlag.