The mechanical structure of the robot mechanical structure and working principle is shown in the sub robot, has the same shape memory alloy spring three sub-sections within each robot, their built-in 120 intervals, fixed on the end caps at both ends of the alloy. Center for the bending stiffness of each to the uniform distribution of soft-core, coated with fiber optic and control lines of the inner core. Ohmic heating SMA spring, SMA contraction phase transition, driven by the cap and the subsequent sections, bending movement. Since the SMA spring is silicone stopper, after bending also curved.
Child robot mechanical model of the robot by a single sub-section of the same structure composed of multiple, single-cell analysis of robot motion control child can get sports model of the entire robot. Child robot single bending beam model can be seen as a soft core axis, the three alloys in tension bend the ends to provide a moment. To simplify the problem, make the following assumptions: the central axis of the bending when the length remains unchanged and before bending the center axis in the cross section perpendicular to the bending axis remains perpendicular to the center; uniform portions of the SMA spring bending stress distribution; response speed due to SMA slower overall bending speed is very slow, so instead of using static analysis dynamic analysis; due to the size and weight of the robot is very small, so the impact of ignoring subsequent sections and the section itself gravity bending beam.
Based on the above assumptions, we can show the child robot with a single beam bending mechanical relationship model. Child robot single curved model sub-section of the end face of the robot is a schematic model of a single curved section is a schematic section of the end face of the child robot. Wherein for each section of the bending angle and in the direction of the bend angle and the OXY plane in that direction; Si (i = 1,2,3) are connected to the three-point alloy and the upper face of which are located a diameter dh , Center for the O's circle; Fi (i = 1,2,3) are in the process of three curved shape memory alloy tension; OO as the central axis, because the three alloys acting on the end face of the beam is pure bending, OO curved its center for P points. As can be seen from, for a single memory alloy spring N1S1, plus one equivalent of the work changing elasticity of the bias spring. Usually in the motion control of the robot, a given target value can be transformed into a bend angle in the direction of curvature, we first derive the following parameters and the bending length and the force of the spring reaches its static equilibrium relationship.
SMA bending parameters and the relationship between the spring force as shown in the coordinate system established on the end face of the O-XY, a shape memory alloy shows a three element position (a1, b1) in the coordinate system, (a2, b2), (a3, b3 ), respectively: a1 = -14dh, a2 = -14dh, a3 = -14dh; b1 = 0, b2 = 34dh, b3 = -34dh. (1) According to the mechanics relations, bending direction by alloy spring tension on the cover Fi launch: tg == F1b1 + F2b2 + F3b3F1a1 + F2a2 + F3a3, = 00 = 0, = 0 <0 =, = 0> 0 = 2 = 0 <0 = 32 (2) three alloys produced in the curved direction of the bending moment M is co: M = dnF1cos + F2cos (23 -) + F3cos (23+).. (3) According to material mechanics calculate the bending angle reaches static equilibrium: = MLEkI.
SMA bending parameters and the relationship between the length of the spring, and shows the relationship between the three SMA spring length. As shown in the coordinate system O-XYZ, Ni, Si and the sub-SMA bending parameters is the length of the clearance face and on the other end surface of the junction point unsprung SMA. Since the SMA spring is bent in an arc with a robot, the arc length is a length of NiSi. If the target parameter and the known bending can be calculated as the length of the section reaches static equilibrium target li three SMA element: the coordinates of point P (Px, Py, Pz) is: Px = (H /) cos, Py = (H /) sin, Pz = 0.SMA arc chord di as: di = (Nix-Six) 2+ (Niy-Siy) 2+ (Niz-Siz) 2.
If the load F of the shape memory alloy, shape memory alloy (SMA) and the resistance temperature T r with a corresponding relationship. Shown by the following equation: T = (F, r). The first shape memory alloy obtained by experiments at different temperatures and the corresponding load data corresponding to the data length and the different loads between the temperature and resistance of the SMA and stored in the database. SMA method using PWM control of the heating element, adjust the duty cycle to control the heating time and heating intensity. SMA informed by the feedback resistor element status.
Multi-section robot motion control sub-robot coordination when crossing pipelines, sub-section due to the proximity of the ends of the parent robot robot motion a great influence on the child, a little mistake it is easy to run into a wall. Will bring unnecessary pain patients when surgery. Therefore, the study of the whole trajectory of the robot and the work space is very important. In order to reduce the working space, we adopt a multi-section and forward motion while bending method. Since the robot workspace is a three-dimensional space pipelines, in order to control more vivid display effect, we use computer simulation to study.
Conclusion shape memory alloy as the driving element can reduce the volume of miniature robots, and flexibility. This paper analyzes the mechanical model of SMA micro-robot system piping neutron robots, target parameters with SMA spring tension and bending target parameters and SMA spring length relationship derived bending static equilibrium, according to the SMA element characteristics under control sub-robot single section of the bending motion of the method to the target position.
