Study On Form Planning Of Archwire And Its Bending Robot

With the development of social economy and people’s living standard, moreand more people begin to pay their attention to oral health problems. Health andregular teeth can not only give people with a good first impression, but alsoimprove chewing ability. Usually, archwire bending is conducted by orthodontistin orthodontic treatment. However, this procedure is boring and time-consuming.Orthodontist has to compare the bended archwire with blueprint constantly toensure the accuracy. When bend angle is too great, unbend it, otherwise, over-bend it. Archwire is easy to be broken after many times’ bend-unbend. This paperproposes to use robot to bend archwire into shape based on the formingmechanism of archwire bending. With the help of the good positioning ability ofrobot, the disadvantage of manual opration can be overcomed and the processingefficiency can be improved greatly.The archwire bending robot and its control system is proposed. The bendingprocess flow of close loop, which is the most complicated part to bend, isanalysed. Then the configuration of archwire bending robot is chosed and theoverall structure, bend die and archwire supporting part is designed, respectively.The key component is analyzed in Workbench. The control scheme of PC+PMACis proposed and the hardware composition, system configuration program,homing program and archwire bending motion program are presented,respectively.The acceleration and deceleration plan of archwire bending robot isproposed. In order to reduce impaction and vibration, a piecewise self-adjustingdistribution plan is proposed to ensure the archwire bending robot’s motionaccuracy. Firstly, a three order pure S acceleration/deceleration curve is proposedbased on the physical parameters of the archwire bending robot. Then, taking the displacement determined by pure S acc/dec curve as the criteria. A5-segmentspure S acc/dec curve is used to planning motion curve when motion displacementis larger than the criteria. On the contrary, a modified pure S acc/dec curve isproposed when motion displacement is less than the criteria. The simulationresults indicated that the proposed method is effective to ensure the good positionablity placidly and smoothly.The control points information of formed archwire is analyzed. First of all,the mathematical model of standard archwire and target archwire with offsets arebuild up, respectively. Then, two methods which are IA (incremental algorithm)and FPDA (finite points derivation algorithm) were proposed to plan the controlpoints. Furthermore, the control points are fitted into curve to compare with theideal curve. Then, the accuracy and efficiency of the two algorithms arecalculated and compared. It turned out that FPDA is much better than IAregardless of accuracy or efficiency. Finally, bend angle at each control point iscalculated based on slope method.The springback mechanism of archwire bending is studied. In allusion to thelarge curvature deformation of archwire bending, archwire bending process isdivided into two steps which are elastic deformation clearly stage and plasticdeformation clearly stage, respectively, in considering the neutral line shift. Thespringback calculation equation of rectangular and circular archwire isestablished based on the constitutive equation obtained from tensile test. Fromthe springback equations we can see that, springback angle increase with bendangle. When bend angle is small, springback angle accounted for a largerproportion in total bend angle. On the contrary, when bend angle is large,springback angle accounted for a smaller proportion in total bending angle.Finally, archwire bending and springback measuring experimentation are carriedon the archwire bending robot system and Olympus metallographic microscope.The experimental results verify the correctness of the theoretical calculationmodel.Choose the oral parameters of one patient, control points and its bend angleare planned with the help of FPDA and slope method proposed in this paper.Then the springback angles are calculated using the theoretical calculation modelbased on the control points. These springback angles will be used to revise the bend angles used in archwire bending experimentation. Finally, the archwirebending experimentation is carried on with rectangular stainless steel and circularAustrilia archwire, respectively. The experimental results of formed archwire aremeasured and compared with the ideal shape. Furtheremore, the error source ofthe experimental results and error reduce scheme are proposed.