A Wounded Transfer Transfer Robot Design Study

For a long time, it is a very dangerous and difficult task for nurses to move seriously injured caused by war or large-scale emergencies and seriously ill hospitalized patients, particularly patients with spinal cord injury from one place to another, such as bed to bed, hospital bed to operating Table, etc. If nurses can not work together softly with manpower, it could cause secondary injury, paralysis in serious cases, or even life-threatening. This paper developed a patient-transfer robot which can work flexibility in the hospital narrow environment, replace the medical staff to handling the wounded, and provide patients and staff a safe patient-transfer concept. Avoiding secondary injury caused by "free" operation. Another purpose was to do pre-research and technical reserves for a new generation of medical equipment "rescue robot" which can enter the battlefield, disaster site, contaminated by NBC, and other inaccessible special occasions.The patient-transfer robot was composed of transfer-arm, Omni-directional mobile chassis, lifting mechanism, wireless controller and control system. Research methods included theoretical analysis, mathematical model, software simulation and prototype experiment. First of all, the paper discussed the physiological characteristics of human skin and subcutaneous soft tissue, builded a simplified human body model by the ANSYS finite element software, and analysed the human body deformation and stress distribution in the total transfer process. The simulation results showed that there is obvious stress concentration between the human and the front transfer arm, the deformation of the bottom of human body will spread, affecting other parts of the wound or incision. The simulation results provided the theoretical basis and guidance for the design of mechanical structure and electronic control strategies of the transfer arm. The design of transfer arm structure was whole-line, with the technology of conveyor belt and relatively static for contact point. The conveyor belt was the isolation layer between transfer arm and the body, its movement direction is opposite to transfer arm, but the same size of velocity. The upper belt and the wounded remain static by the same velocity of conveyor belt and the patient relative to the transfer arm, to avoid sliding friction effects, so that the wounded can be transferred safely and painless. The Omni-directional mobile system was compose of four-wheel independent drive Mecanum wheel, it can move forward, reverse, lateral and rotating around its own, get full three degrees of freedoms on the motion plane with the synthesis of four wheel steering and speed. That is why patient-transfer robot had more mobility, flexibility and precision targeting. According to the actual needs of their own characteristics, the electronic control strategy of transfer arm and the Omni-directional mobile chassis formed by the selector, observer or self-organizing fuzzy controller. The selector can choose appropriate control parameters and variables under different loading conditions. The observer can estimate the absolute displacement of the human body, and control the human body deformation within the physiological range, to avoid the discomfort of the wounded. The self-organization fuzzy controller can continuously do self-learning, improve system performance, make the motor to has a good following characteristics, change with the base motor, overshoot suppression systems, reduce adjustment time, and thence improve the precision and the dynamic stability of the transfer arm and the Omni-directional mobile chassis. The manner of the speed control of the Omni-directional mobile system was non-uniform level, and the technology of picking up the signal of the joystick was the A/D programmable interrupt control. It effectively improved the accuracy of low velocity and eliminated the artificial jitter caused by manipulating the joystick in the high-speed movement. In order to positioning accurately between robots and beds or the operating tables, etc, we designed jog-program to make the control of robot to be more simple and human.The paper designed the mechanical structure and the electric control system of the robot on the basis of the theoretical analysis and structural design. We completed all the parts with the three-dimensional maps and engineering drawings of patient-transfer robot by the SolidWorks 3D Design Software, assembled into a robot, and did calculation of weight, crash tests, interference check, stress analysis and motion simulation of small assembly by the software module. To compute the power of drive motor, the size of conveyor belt and the spring force of preload spring, etc, for choosing the device type, to achieve the robot's design specifications and features. According to the hardware circuit, the system software design must follow the software design specification, highlighting the practical and relevant, not only to achieve the robot's functions and improve operational precision, but also to take into account testing, scalability and maintenance. The program emphasized the system design of security and reliability, and strengthed the monitoring and processing capabilities of conflict and the failure.The main experiments included debugging hardware and software, separate experiments, model experiments, tester experiments and evaluation. The debugging of hardware and software were to solve the possible failure of hardware or conflict of software before the experiment online. The separate experiments were to verify the feasibility of working principle, mathematical model and control strategy of transfer arm, elevator, and the Omni-directional mobile system, etc. The model experiments were to verify the machine performance, security and reliability of the robot. The subjects of testers experiments choosed the different weight and age men and women, the subjects have orthopedic and obstetricians who long been engaged in clinical surgery, nurses and researcher in medical equipment, etc. The "trust", "comfort" and "psychological experience" survey of the subjects before or after experiment showed that many subjects have more or less emotional or psychological stress skepticism on the patient-transfer robot, but it almost gone after experience. They confirmed transfer functions of the patient-transfer robot which has a certain practicality.Innovation: (1) The patient-transfer robot was developed with the Omni- directional mobile system and the whole-line design of transfer arm, got all three degrees of freedoms on the motion plane with high mobility, flexibility and precision positioning capabilities. (2) The initial finite element analysis simulation results of patients provided the theoretical basis and guidance for the design of mechanical structure and electronic control strategies of the transfer arm. (3) The transfer-arm was developed with the technology of conveyor belt and relatively static for contact point can transfer patients painless and safely without moving the body.Conclusion: The patients who lie still in bed can be transferred painless and safely with the patient-transfer robot which can be controlled by wireless controller without manpower in the transfer process. The patient-transfer robot can adjust the vertical distance automatically, move flexible in the full three degrees of freedoms on the motion plane, and locate accurately. The prototype of the patient-transfer robot achieved its design goals.