Designing 6 degrees of freedom rotary stewart platform and positioning using tilt sensor during the surface roughness measurement

Today control and automation systems are the latest technology of the mechanization process which starting in the year 1700. Automation sytems are the easiest and most safest solution especially for the manufacturing a product which requires a lot of production time, highly labor power and contain risks for humanity. During the serial production, control process is as important as production of the products especially when the products are safety parts which have dimensionally critical characteristics. Therefore it is one of the most important issue to making the process independent of human attention. Today parallel and serial manipulators found themselves in the industial applications where the process requires safety, stabilization, pace and independence of human attention. Although the serial production providing short time manufacturing process with lower cost, control process to detection of the defective products becomes very difficult even sometimes imposssible. Therefore to ensure the reliability of the production, process parameters must be monitored interpreting the results of the statistical analysis. For this purpose statistical process control is a calculation which provides mathematical data to measure required capability of a manufacturing process. But also, statistical process control analyzing distribution of the measured data within the tolerance limits for each production process, it is not only provides existing capability, qualification of the future production is also taken into account. Therefore, in order to find an adequate process value as a result of statistical process control calculations, it is not only requirement to ensure dimensions within tolerance limits but also deviation of the dimensions always must be demonstrate uniform distribution. Because of the inadequate process capability values of the statistical analysis requires constantly detection of the related dimensions of the products which causes significant increase of the production cost, it is very important to ensure precise conditions during the measurement for the statistical process control. Statistical Process Control (SPC) is an industry-standard methodology for measuring and controlling quality during the manufacturing process. Quality data in the form of product or process measurements are obtained in real-time during manufacturing. This data is then plotted on a graph with pre-determined control limits. Control limits are determined by the capability of the process, whereas specification limits are determined by the client's needs. Data that falls within the control limits indicates that everything is operating as expected. Any variation within the control limits is likely due to a common cause the natural variation that is expected as part of the process. If data falls outside of the control limits, this indicates that an assignable cause is likely the source of the product variation, and something within the process should be changed to fix the issue before defects occur. Surface roughness measurement tend to change especially for the surfaces which produces without machining operation. Most important cause of faulty measurement values during the measurement of the surface with the profilometer is location failure between measurement tip of the profilometer and the related measurement surface which requires exactly 90 degree to achive best result. While collecting data forstatistical process control, same dimension of the parts measuring in many times, with every times different part and measurement tip location causes measurement failure and non-uniform distribution of the deviations. In this case, the produced product, although having the required process capability, leads to continuously kept under control which causes increase of the cost and sometimes even leads to scrapping of the correct products. This study aims to significantly increase process capability values as a result of the statistical process control analysis of the surface measurement and reduce time lost in the preperation of the measurement products during this studies which allows to production of the high quality products with lower cost reqirement. A parallel robot stewart platform that works rapidly and precisly is the most important system which planned to achieve this purpose. Stewart platform is a parallel manipulator device that is used for positioning and motion control. The device consists of two plates joined by six adjustable legs that allow it to be precisely adjusted and controlled. Due to the six-leg design, the stewart platform is sometimes called a hexapod. The term can be used to describe any six-legged device. The stewart platform is also classified as a parallel manipulator, meaning that the legs of the platform are attached to only the base and upper plate but not to each other. By contrast, a serial manipulator uses a series of rigid structures connected by joints. The manipulation of one of these rigid sections directly affects the positioning of the sections after it.Although originally used to test tires, the stewart platform soon found applications in the aerospace, automotive, and machining industries. It is perhaps best known for its use in providing the precise movement required of flight simulators. In this study the stewart platform will be created by stepper motor due to lower cost and accurate positioning instead of pistons unlike literatures. Force-balance inclinometer sensor will be utilized for positioning of parallel robot as tilt sensor and measured value will be send from microprocessor of inclinometer to microprocessor of the stewart platform via serial communication between them. In this study current surface measurement technologies and structure of mechanical profilometer were described in detail, SPC methods which uses for calculation to capabilities of the process in experiments are mentioned. Design flow chart was created for positoning measurement sample to proper location and design requirements were determined according to the chart. In this context the Stewart platform was designed by 3D programme. Stewart platform's position control was carried out by an algorithm that developed by inverse kinematics calculations. 3D actualized design was modelled mechanically in Simulink programme and movement was observed via inverse kinematics simulation after necessary motion limit assigned and geometrically calculated inverse kinematic analysis verified. Available technologies of the tilt sensor investigated theorically for the selection of appropriate sensor to measure inclination values of the surface which will be positioned to perfect measurement tip and the measurement surface location. Mechanical structure of the stewart platform, system structure and circuit structure of microprocessor of the stewart platform's actuators and the microprocessors of the inclinometer sensor and their serial communication systems are described. In conclusion, utilizing the precise positioning capability of the parallel manipulators we ensure that surface which will be measured by profilometer postioned 90 degree with the measurement tip of the profilometer for each measurent during statistical analysis. Statistical methods and calculations which required necessarily for the parts having critic characteristics such as given in this study are described and contrubition of given automation system to statistical process control was investigated. Through the proposed solution statictical capability of the surface measurement process increased and control frequency of the products reduced significantly which leads to production cost reduction. Provided increase of the process capability ensured that frequency of the statistical process control analysis which requires for critical characteristic measurement reduced from every production to every two weeks. Samples which are going to be positioned through a rotational RSS-SPM in surface roughness measurement is applied for the first time with the generated system and while surface roughness measurement process .becomes independent from attention of operator, contribution of generated system was investigated.