| Currently, the tool for transporting patients between operating rooms and hospital beds is mainly ordinary mobile beds. This way of transporting has serious shortcomings as follows:(1) It is basically relied on the help of medical personnel for patient to get up or lay down on the hospital bed. This method is not only inefficient, but also likely to cause physical injury to health care workers such as strains, sprains and other accidental injury.(2) The strength and posture for medical personnel to handle the operation of transporting cannot be standardized, which might impact on the patient’s body easily, especially for the patient who are spine damaged or after doing surgery. In that way it would cause further injury to the patient, even life-threatening.(3) The operation of transporting hospital bed is mainly handled by manpower, health care workers will be vulnerable to infection or be threatened their health at the time when the patient is suffered from infectious diseases. When large-scale disaster happens suddenly, the number of wounded would increase dramatically while the number of medical staff is limited. The seriously injured cannot get timely treatment in that situation. The wounded transport robot is mainly used for transporting the wounded painless and safely. It can not only relieve the wounded fast and effectively and reduce the workload of rescue personnel, but also can protect the personal safety of the rescue personnel effectively when they are doing jobs in the battlefield. Research group developed a robot for transporting the wounded which based on a full range of mobile chassis Mecanum wheel. The robot can move in any direction in hospitals and other crowded, narrow space environment, its chassis has a high degree of freedom of movement and the capability of precise positioning as well as semi-autonomous operational capability which makes the robot can make alternative transport wounded transfer them into the infectious ward, isolation ward and other hazardous areas to perform nursing work. The arm of the transfer robot is overall line designed. By the use of conveyor technology and the relatively static contact point technology, painless transfer without the need for moving patients is achieved, that is helpful for patients especially for the burned or spinal injured which can prevent secondary damage caused to the patient effectively. In addition, the robot is simple to operate and can automate handling of the wounded which effectively reduces the labor intensity of health care and provide effective solution to the problem of changing bed between hospital beds, operating table and checking devices.Through summarizing the data and questionnaires about the subject of the wounded transport robot, the following shortcomings were found:(1) The regularity of vibration phenomena occurs during the movement;(2) When driving straight along the X, Y axis, the deviation between actual trajectory and the preset trajectory is large;(3) When a wheel slippage occurs, it will lead to the vibration of the robot which will affects its smoothness when walking. The purpose of this research is to analyze above questions, improve and optimize the chassis structure, control systems and software procedures of the robot in order to improve the controllability when nurses are using it and the comfort of the wounded.This paper optimizes the mechanical structure and control system of the omnidirectional mobile robot chassis of the wounded transport robot in response to the problems above-mentioned, its main contents are as follows:The second chapter of this paper studies the cause of the periodic vibration which occurred during the motion of the wounded transport robot. Firstly, the structure of Mecanum wheel composition is introduced and the intermediate segmented support structure is selected according to the actual situation and the characteristics of the small roller. Then the theoretical outer profile of the small roller curve equation is calculated according to the structure. According to the layout of omnidirectional mobile chassis and omnidirectional mobile principle, a plane coordinate system is established by using a single Mecanum wheel as research object to conduct in-depth study of omnidirectional mobile technology principles, calculate its mathematical motion model and determine the relationship between omnidirectional chassis mobile means and the speed of four wheels moves. Then according to the working conditions of Mecanum wheel, the force analysis of small roller wheel is carried on. On this basis, finite element analysis of the r oller rubber shell on Mecanum wheel is conducted using the ANSYS simulation software. Through the analysis, the periodic vibration of omnidirectional mobile chassis is mainly caused by the extrusion deformation of the roller rubber shell.This chapter uses the amount of deformation of rubber outer contour to compensate its corresponding position and fix the amount of compensation for each roller according to the coincidence degree, on this basis, through adding the lateral pattern to absorb the extrusion deformation of rubber shell, not only can the falling off of the rubber be prevent, but also can the smoothness of the omnidirectional mobile chassis when it is moving be improved effectively.The third chapter in this paper studies the omnidirectional mobile chassis control system of the prototype of the wounded transport robot, in connection with the track offset phenomenon occurred during linear motion of the wounded transport robot, posture sensor which can measure its heading is introduced in, and then the fuzzy control strategy based on heading is developed. In this paper, the date collected by gyroscope, accelerometer and electronic compass is using to provide real-time heading information for the designed control strategy through attitude algorithm of the omnidirectional mobile chassis based on quaternion Kalman filter. To ensure that the feedback of the motor speed regulation is kept within reasonable intervals, the upper limit to revise heading is determined based on the current speed of the motor, so as to avoid the phenomenon of vibration caused by excessive adjustment or the problem of costing too much time rectifying deviation caused by adjusting too slow.Chapters IV and V of this paper designs the hardware and software of the omnidirectional mobile chassis. The overall structure of the control system of the the omnidirectional mobile chassis is introduced which is mainly composed by the operating handle, a microprocessor (MCU), the drive motor control, posture sensor (IMU) and the motor. Its research mainly contains the following areas:1. Communication between the master controller and the operating handle: whether the master controller can communicate with the operating handle and the communication data affect the operational state of the omnidirectional mobile chassis directly. To ensure the accuracy of the communication data of the operating handle, CAN bus communication circuitry is designed in this paper. And communication baud rate and communication ID are set according to the operating handle communication protocol to ensure the normal communication between the master controller and the operating handle.2. The extraction and Improvement of date from the operating handle: Appropriate software program for extracting data from each axis is written in accordance with the operating handle data format. In actual operation, the shake of hand is likely to cause the deviation of date, thus affecting the accuracy of moving and handling of the mobile platform. This paper extends the effective range for each axis and selects the range of reasonable and effective range to avoid bias because of the shake of hand as well as ensuring the sensitivity of the platform.3. The solver of motor speed and the design of driving circuit:The omnidirectional mobile mathematical model is improved according to the installation of the platform motor. The solver of the data of the operating handle is conducted to obtain the magnitude and direction of the motor speed according to the model.The motor speed is proportionally converted to PWM pulse, and then the pulse is converted to the analog voltage signal by the RC circuit in order to control the motor drive. Reasonable handle acceleration curve is set to improve the stability and maneuverability of the omnidirectional mobile chassis.4. Posture sensors (IMU):The module of each component of the posture sensors is introduced as well as the means of communication among each module. Posture sensors exchange data with master controller via USART interfaces, in order to ensure the accuracy of the data exchange, certain data frame format is used between data exchange. Only when the checksum is correct, the data received will be processed. The fuzzy control arithmetic course based on heading would be completed in IMU master controller chip. The speed of each motor after revising would be send to the master controller to realize the adjustment of the motor based on heading. In the sixth chapter, load deformation tests are conducted on the optimized roller to verify the accuracy of its finite element analysis. The IMU gyro module is used to test the vibration characteristics of the omnidirectional mobile chassis which verified the improvement of the stability after optimization.The walking track of the omnidirectional mobile chassis is collected by the photoelectric trace collector to verify the validity of fuzzy control method based on heading.Chapter VII summarizes the full text and brings out the following two suggestions for the future research:1. Improvement for the Mecanum wheel structure. Due to structural characteristics of Mecanum wheel, vibration phenomena will be inevitable during walking which will affect the omnidirectional mobile performance. The theory for the compensation of the Mecanum wheel profile needs in-depth study to improve the walking ability although the profiles of Mecanum wheel is revised in this article and the results improved significantly.2. In this paper, the solver of the omnidirectional mobile chassis is achieved based on quaternion Kalman filter. However, with more serious vibration or the magnetic interference, the results will appear large deviation which affects the control accuracy. Therefore, further study based on multi-sensor posture algorithms is necessary to lay the foundation for the control of the omnidirectional mobile chassis based on heading.Both the mechanical structure and the control method of the omnidirectional mobile chassis developed in this paper have been improved. The main innovation of this paper has the following two aspects:1. The software ANSYS is used to analyze the deformation of the small roller while it is working, the outline curve of the small roller is optimized and the stability of the omnidirectional mobile chassis while it is running is improved. 2. By using the posture sensor which is composed by gyroscopes, accelerometers, and the electronic compass, the real-time heading of the robot is measured. To revise the speed of each motor by using the fuzzy control method based on heading, the capability of linear movement of the omnidirectional mobile chassis is achieved and the controllability is improved. |
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