外文原文--Mechanism Design and Simulation Analysis of Multifunctional Nursing Bed

Mechanism Design and Simulation Analysis of Multifunctional Nursing BedLizong Lin, Song Zhang, Xinglong Hu School of Mechanical and Power Engineering East China University of Science and Technology, Shanghai, China E-mail: E-mail: Abstract-This research develops a new multifunctional nursing bed that can realize the movements of turning left and right sides and defecating on the bed for clinical use. And use the ADAMS to analysis the effects to the motor torque from the force on the rotated board, friction of contact pair and space position. By analysis of dynamic on the model of the main mechanism can get the curves and the influences of torque, which plays an important guiding role in selecting appropriate motor and installation structure.Keywords- nursing bed, ADAMS, virtual prototyping, dynamic analysisI. INTRODUCTIONNursing beds as parts of medical equipments are necessary for hospital care, and has been widely used in hospitals, nursing homes, retirement homes and many other fields. However, the prices of good quality nursing beds are expensive, the new study can reduce the cost and the difficulty of care, for example, to the patients resting on the bed for a long time, their turning over and lifting back required nurses have sufficient physical strength. Common beds just have head up, leg flexion and extension functions, this bed adds the function as rolling around, defecating on the bed and so on as needed 1.II. MECHANISM DESIGNThe nursing bed can be divided into four parts by the structure and function as: bed body, control cabinet, a framework for activities, removable bedpan. Block diagram as in Fig. 1In the control cubicle, the installment has the master control board, the motor-driven board, the transformer, the switching power supply and so on. The control cubicle connects with the nursing bed by the connection. Except the fixed mechanism, the bed body also includes the drive motor and the vane organization. The active frame installment has the wheels, which may be separated from the nursing bed. In the frame there are the water tank, stool which can rise and fall and the hot air blower. The transportable bed pan also installs wheels and can insert into the activity frame. In addition, the control system also includes the wire operators, the LCD and so on. In the system there are six DC motors which complete the actions of rising and falling of the head, the flexion of the leg, rolling around of the left and right, opening and closing of the vane and rising and falling of the stool and so on.A. Bed Function.The bed activity functions including the rising and falling of the head, the flexion of the leg and the bed body tum sides which satisfied patients active request basically, favors the patients to improve their blood circulation and prevents the bedsore. This nursing bed has designed the flexion of the leg conforms to human bodys movement characteristic. The bed body side turns may divide into three movements: the left side to tum, the right side to tum and the even side. Fig. 2, Fig. 3, Fig. 4 is the bed bodys three movements. B. Nursing Function The defecation function is rare in other electric nursing bed which suits the paralysis patient especially. In the middle of the bed body there is a rectangular opening, where can only seen two vanes in the normal condition. When defecating, the vane turns down to makes a breach, then the defecation device rise. After the defecation completed, the vane upturns continues to fill the gap. The defecation device is composed of the active frame and the motion bed pan which can inserts into the frame, and the entire frame can coordinate to load the bed body. The nursing bed can also provide the functions of spraying water and drying. In the active frame installed the water tank, the hot air blower and the solenoid valve. The water tank has a water pump, heater, the temperature sensor and the water level sensor. It can be realized that the water temperature establishment, the water temperature maintains and the water tank volume automatic increase and so on under the controllers control. The patient who is sick bed in long-term is the major recipients of this nursing bed. Before defecate, press the key stool raise on the remote control, two vanes open, and then the stool raise, plate of the stool erects automatically, and so as to the bed pan. The patient can defecate after these movements completed. After the defecation completes, press corresponding key, carries on the flushing first, then uses hot blast drying, which has manifested the human nursing function. The water for flushing is preserved in the tank, and use heating wire to maintain the temperature. Its needed to gather and process of the temperature in order to realize the control of it, the gather can completed by the sensor, the process and control can completed by the monolithic integrated circuit. As a result of the patients defecate time is uncertainty, and requests maintains the temperature constant, for the aim of providing appropriate temperature momentarily.III. SYSTEM MODELINGA. Modelling Nursing bed is a very complex structure, which can divided into the mechanical component of the bed body, the active frame, the transportable bed pan, the electronic control system and the motor driven system by the structure and the function. Fig. 5 is the geometric modeling graph of the vane 2.I Right rotated board 2 lever of right rotated board 3 Driving arm of right rotated board 4 Motor of right rotated board 5 Motor of left rotated board 6 Driving arm of left rotated board 7 lever of left rotated board 8 Left rotated board 9 Door axis of rotated boardFigure 6 Lever and driving arm of rotated board I Lever of rotated board 2 Driving arm of boardB. Contact Pairs Processing Fig. 6 is the geometric modeling graph of the vane lever and actuating arm. The axis of one of the vane lever ends fixed with the vane, the other end has a curve groove. Both sides of the vane actuating arm are round axes, whose axle centers are parallel. One axis is linked with the motor and fixed, the other coordinated with the curve groove to form a contact. The motor caused the actuating arm to reverse, which can realize opening and closing of the vane.III. SIMULATION ANALYSIS The purpose of dynamics simulation of the vane is to analysis the influence to the torque in the different condition, and guide to improve the design and select the appropriate drive motor 3. A. !influence to Torque from Action The sizes of the left and right vanes are not equal, but the motors are same. Select the right one which has a greater area and force to analysis 4. Select the action point in middle of the two vanes, and the arm of the force is 15 cm. The friction coefficient of the steel is 1.2 to 1.4, and 0.02 to 0.05 after lubricated, takes the friction coefficient of 0.05.The curves are not smooth seen from Fig.7 and Fig.8, as the high frequency component coupling to them analyzed mathematically, which were considered to be vibration in actual. It is also discovered that the vane has a phenomenon of vibration, which meet with the simulated data when testing. The vibration has a relation to the stress, nature of material, rigidity of material, osculating curve of rigid body, friction coefficient and so on. It is inferred from the simulation analysis that the bigger stress the smaller vibration. Make sure the contact surfaces are smooth when design the curve groove of the vane lever to reduces the nonessential vibration. Fig.9 is the angular velocity when the stress is SOON, the vibration situation can be observed obviously 5.The actual action to the vane from the patient is not constant but increases gradually when the vane turns to the level position nearby. So that, select the larger motor torque as far as possible to prevent overloading.B. lrifluence to Torque from Friction CoefficienttThere are three kinds of restraints altogether in the vane simulation: fixed restraint, hinge restraint and contact restraint. The fixed restraint cannot cause the friction force, but the hinge restraint and the contact restraint can. The hinge to the hinge restraint can be processed as sliding bearing. The friction coefficient of sliding bearing is small. The dynamic friction coefficient of sliding bearings is 3.0xl0-3 and the static friction coefficient is 4 .0 x 10 - 3 Although the contact restraint is also a kind of sliding friction, but it cannot simply processed as sliding bearing, because the contact is complex, and the stress is also big. Fig. 10 represents the contact force when lever axis and curve groove of actuating arm have a stress of SOON, where the biggest can reach 1800N.Fig. 11 and Fig. 12 respectively represent the torque chart in the friction coefficient of 0.07 and 0.31, and the stress of SOON.Compared with Fig. 11 and Fig. 12, it cannot obviously see the changes of the torque, so as the curve. The biggest diversity is that the vibration reduces when friction coefficient is 0.31. The friction coefficient f.I. has not caused the biggest moment of force change obviously, only has a tendency of enlargement, after the process of filter smooth correlative value 6.C. lrifluence toTtorque from Space PositionWhen design the vane, not only consider the actual installment space and the request size, but also need to pay attention to the relations in the space position between the revolution axis of the vane lever and the revolution axis of the actuating arm. Because their positions are not only relating whether the vane can operation normally, but also affects the biggest driving force. Use the coordinates system as Fig. 13 when establish the coordinate. Fig. 14, Fig. 15 and Fig. 16 are the changing graph of biggest torque in VI-452 Volume I 2010 2nd International Conference on Mechanical and Electronics Engineering (ICMEE 2010) different space position 7. And the stress is SOON, friction coefficient is 0.03.Comparing the data in the different condition may see that the time and the biggest torque have changed remarkably. And the movement time is the smallest in condition 3, so as the force moment. In the condition 2, the lever arm separated from the drive shaft in the moving procession. When actually determine the data, should consider about the motor of torque, size and structure and so on, the best effort may not be the most suitable 8. Through the analysis of dynamics simulation to the vane that: 1) The motor driven torque is small. In the process of simulation analysis, exerted 500N force to the vane and calculates the biggest torque of the motor is 25Nm, but actually the torque is 18Nm, therefore present the phenomenon of the vane asthenia when raising. Here takes 500N force, it is only the average action size in the normal condition. When actual use, possibly bigger than 500 N, so that it must be considered that the motor should have a sufficient remainder actuation torque to satisfY the request under the dissimilar condition. 2) The influence of the friction coefficient is not big to the torque. Under the condition of constant action, its indicated that the friction coefficient has a very small influence to the torque, through takes different friction coefficient to calculate the biggest torque. 3) The space position of the rotation axis has a bigger influence to the torque, the condition 1 and 3 have a difference of 1 ONm, and the movement time also changing.V. CONCLUSION Discussed the influence factors include the driving torque action, friction coefficient, space position and so on by the dynamics and the kinematics analysis to the vane of the nursing bed, which improved the theory basis to the design of the structure, and provided the science basis to the performance evaluation analysis of the bed. This bed may also increase the network communication function to the system, which will cause it to be able to transmit the information automatically to the superior machine, an