Design of multifunctional self-balancing nursing bed based on SolidWorks

1. Introduction

This paper combines the model and composition characteristics of the multifunctional automatic balancing nursing bed, and based on the SolidWorks 3D parametric design process, conducts an in-depth analysis of its parametric design, assembly and motion simulation, workspace analysis, and kinematic analysis. This paper completely abandons the parametric design idea and focuses on the practical problems of the multifunctional nursing bed. This solution is also applicable to the research and development of other similar medical care equipment.
This paper will explain some key issues in the design process of the multifunctional automatic balancing nursing bed, and will not repeat the content of parametric modeling and other aspects that are currently introduced in relevant literature.

2. SolidWorks 3D Design Process

At present, there are many articles about SolidWorks in the design of medical beds and nursing beds, most of which focus on parts modeling, virtual assembly, motion simulation and finite element analysis of parts, etc., which only highlight the characteristics of SolidWorks software or the local functions of a nursing bed. There has not been a systematic study centered on the design of multifunctional nursing beds. SolidWorks is just a tool, and tools must serve the design object, which is also a point we emphasize in the design process.

Figure 1 is a technical flow chart for 3D design in SolidWorks. The main body of this process is a parallel design process. In this process, the design scheme is first determined, followed by 3D modeling and modeling, and the focus is mainly on part modeling. After modeling is completed, assembly is performed, and static interference analysis and local modifications are performed. After the scheme is confirmed, motion simulation analysis is performed to modify the dynamic interference that occurs during the movement. After confirming the basic dimensions, finite element analysis can be performed on key components to determine whether their mechanical properties meet the work requirements, and structural optimization is performed on this basis. After optimization, finite element analysis needs to be performed again until the final scheme is determined. Two-dimensional drawing and processing are some follow-up work, which is omitted here. By- product model analysis and function introduction #e#3. Product model analysis and function introduction

The overall scheme of the multifunctional automatic balancing nursing bed is shown in Figure 2, which consists of a bed body, fixed support rods, servo hydraulic cylinders, electric cylinders, a walking frame and a control system.

1.Structural composition and functions of the automatic balancing system

As can be seen from Figure 2, the upper surface of the platform, i.e., the stable surface of the platform, is supported by four ball joints. For the two-degree-of-freedom platform, the fixed rod 3 is fixedly connected to the base frame, and the electro-hydraulic servo cylinders 4 and 5 are symmetrical about the rod 3 and hinged to the base frame, and the three are in a straight line. The hydraulic servo cylinder 9 is on the same midline as the rod 3 and is also hinged to the base frame. Under the control of the three servo cylinders, the platform can perform pitch motion around the horizontal axis passing through the fixed support point and swing motion around the longitudinal axis of the fixed support point and the constraint support point, so as to achieve the purpose of keeping the stable surface horizontal when the base plate shakes.

2. Body position adjustment function

According to the principle of ergonomics, the bed is divided into three parts: back plate 1, seat plate 2 and leg plate 6. The back plate and seat plate are hinged by shafts. The back position can be adjusted from 0° to 85° by controlling the extension and contraction of the electric cylinder. Similarly, the angle of the leg plate can be adjusted. In this way, the continuous position adjustment function between sitting and lying positions of the bed is realized, as shown in Figure 3.

3. Bed upright function

The support rod system of the whole bed mainly consists of two parts: the fixed rod 3 and the electro-hydraulic servo cylinder 9. The extension and contraction amount of the electro-hydraulic servo cylinder 9 is controlled to make the bed body rotate around the ball joint of the fixed rod 3, thereby realizing the angle adjustment of the bed body within the range of 0° to 80°.

4. Key issues in model assembly design

In 3D modeling, the multifunctional nursing bed is basically a standard model construction, and is rarely used in complex surfaces. Issues that need to be considered include parametric design and processing, industrial modeling and overall processing, and parts serialization.

1. Parameterization problem

In the design of nursing beds, parameterization is mainly reflected in two aspects, namely part modeling and assembly. For part modeling, parameters can be divided into three categories:

(1) There are certain constraints between them, and parameters cannot be changed at will. For example, the size parameters of the motor are like this, and they must be obtained by referring to the relevant technical parameters.

(2) Obtained from relevant manuals, but can be modified according to actual conditions.

(3) Determined based on specific circumstances.

In the process of part design, parametric sketch modeling should be used. First, complete the ideal structural shape according to the design requirements, and then assign dimensional constraints or geometric constraints to each curve so that the curve can be updated and exchanged according to the designer's intention to generate parametric features. Among them, it is easier to achieve full constraint drawing with sketches, while solid modeling needs to consider the influence of Boolean operations. Through this modeling method, it is easy to realize the modification and deformation design of parts, and other similar parts can be generated without re-modeling, which can significantly improve design efficiency.

In the assembly process, there are inheritance and constraint relationships between many parts, such as the inner diameter of the hinge hole of the hydraulic cylinder piston head is equal to the outer diameter of the mounting pin . When changes, it also changes accordingly, and the equality relationship between the two is established through expressions. At the same time, since the two require matching, alignment and other constraint relationships during the assembly process, when the position and size of a part changes, the position of the matching part can also be automatically changed through this positioning relationship, thus ensuring the consistency of the constraint relationship between the parts, facilitating product design and parameter modification, or using this as a template for parametric design of serialized products.

2. Parts serialization problem

In the design of nursing beds, parametric modeling is very important, but not all parts need to go through the parametric design process every time. Instead, a parts library can be established. In SolidWorks, for common standard parts (such as bolts, etc.), it is recommended to directly create a library and call it. For factory-standard serialized parts (such as thrust bearings), they are similar in appearance and structure, but have different geometric dimensions and some minor features. At this time, you can first create a part template and list the important dimensions to be changed in the table provided by SolidWorks, thus forming a part family. When you need to call it, you can directly change these dimensions in the table to generate new parts, thereby shortening the design and assembly time.

3. Industrial styling and overall design

In foreign countries, industrial modeling is the beginning of all design work, and it is combined with the overall design in planning. In the design of nursing beds, the design and rendering of the bed body are closely related to industrial modeling. The design of the bed body should not only consider the human-machine environment, but also the material selection and streamline design. Here, the surface modeling function of SolidWorks is used to complete the bed body design. In addition, after the three-dimensional solid model is established, it is necessary to produce realistic nursing bed products and component renderings through advanced rendering. A good rendering will bring good results to the promotion of the product.

5. Structural Verification of Assembly and Motion Simulation

1. Key issues in assembly

The assembly mentioned here refers to static assembly. The assembly process will not be introduced here. The problems that need to be solved in actual design are as follows.

(1) Assembly mode. In the assembly of a multifunctional nursing bed, either the top-down or down-top method can be used. The two are not contradictory. In fact, they are a parallel process and are often used interchangeably.

(2) Interference check. For nursing beds, interference analysis must be performed on all components to avoid interference collisions during trial production. Since the machine is complex and has a large number of parts, it is impossible to solve the problem by repeatedly producing prototypes. Instead, it is necessary to minimize such errors during the design phase. The interference function in the SolidWorks assembly module can solve the static interference analysis of the entire machine, such as between the thrust bearing and the bearing ring. This is a commonly used method.

(3) Tolerance issues. The 3D models of static assembly are all in an ideal state, that is, models without tolerance. This is of little reference value in the actual working environment, because the processed parts all have deviations. Therefore, it is also necessary to consider the impact of different tolerance conditions on part assembly. In contrast, interference checking only checks ideal dimensions and collision conditions.

SolidWorks module is used to analyze and synthesize tolerances of the entire process of parts and assembly, so as to analyze the impact of part tolerances on product accuracy and whether the assembly model meets the accuracy requirements. The constraints and sensitivity of key dimension tolerances that affect assembly relationships and assembly accuracy are determined, and manufacturing costs are reduced by changing the tolerance constraints of individual key dimensions. Tolerance indicators are relaxed on the premise of meeting product accuracy, performance and technical indicators, so that the dimensions meet the expected accuracy requirements of the product within a looser tolerance range, thereby reducing manufacturing costs.

2. Motion Simulation

There are two functions for motion simulation: dynamic interference analysis and analysis of motion laws. The Simulation module in SolidWorks can perform motion simulation analysis (Figure 4) to observe the interference relationship between components during motion, such as possible collision interference between the hydraulic cylinder and the bed. In motion analysis, the displacement, velocity and acceleration curves can be used to observe whether the motion law meets the design requirements, as shown in Figure 5.

Workspace Analysis #e#6. Workspace Analysis

The robot's workspace is the working area of ​​the robot manipulator, which is an important indicator to measure the robot's performance. According to the posture characteristics of the manipulator when working, the workspace can be divided into a reachable workspace and a flexible workspace. The reachable workspace refers to the set of all points that can be reached by a reference point on the manipulator, and this workspace does not consider the manipulator's posture. The flexible workspace refers to the set of points that can be reached from a reference point on the manipulator from any direction.

1. Factors affecting the workspace of the nursing bed platform

(1) Limitation of rod length. When the length of a rod changes, it is limited by its structure. The length of each rod must satisfy: , where and represent the shortest and longest values ​​of the i-th rod, respectively. When the length of a rod reaches its limit, the reference point on the motion platform reaches the boundary of the workspace.

(2) Restriction of the rotation angle of the revolving pair. The rotation angles of various hinges, including spherical hinges and universal joints, are subject to structural restrictions. The rotation angle of each hinge is , where is the maximum rotation angle of the spherical joint and universal joint of the i-th hinge, and its size is determined by the specific structure of the kinematic pair.

(3) Dimensional interference of rods. The rods connecting the moving platform and the fixed platform have geometric dimensions, so the rods may interfere with each other during movement. Suppose the rod diameter is a cylinder. If the distance between the axes of two adjacent rods is , then .

2. Determination of the working space of the stable platform of the nursing bed

The area of ​​the upper platform is 1500×1000 ( ), the minimum length of each hydraulic cylinder is 1000mm, the maximum extension is 800mm, the swing angle of each Hooke joint is ±45°, and the swing angle of each ball joint is ±45°. Satisfy:

The workspace is obtained by MATLAB simulation, as shown in Figure 6. Analysis of the results shows that the green area is the safe working area of ​​the stable platform, and the red area is the dangerous working area of ​​the stable platform. According to the actual project, the adjustment range of the stable platform is generally in the green area.

VII. Conclusion

The biggest advantage of 3D design simulation technology applied to medical care equipment is its integration, rather than simply focusing on parametric modeling. This article adopts the design of a multifunctional self-balancing nursing bed based on SolidWorks, and elaborates on multiple aspects such as physical assembly, motion simulation and workspace. Its basic functions include automatic balancing, bed and wheelchair conversion, and bed uprightness, etc. It is suitable for hospitals, homes, ambulances and large ships, etc.