Method for analyzing key characteristic parameters of crank rocker mechanism based on Catia

Abstract

The invention discloses a method for analyzing key characteristic parameters of a crank rocker mechanism based on Catia. The method comprises the following steps that 1, the instantaneous transmission ratio i of the mechanism is obtained according to the three-center theorem; step 2, obtaining a transmission angle gamma and a pressure angle alpha of the mechanism on a Catia sketch interface; and step 3, further obtaining a pole position included angle theta of the mechanism, and calculating a travel speed coefficient k of the mechanism according to the pole position included angle theta. According to the method, rapid iterative calculation can be carried out in the Catia sketch environment, key design parameters of the crank four-bar mechanism can be visually displayed by modifying the lengths of different bar pieces and the angles of the driving bar pieces, the method can also be similarly popularized and applied to a multi-bar mechanism and other derivative mechanisms, time and labor are saved, the intuition is high, iteration is rapid, and the method is suitable for large-scale popularization and application. Key index parameters are output quickly, and the method is completely suitable for an engineering preliminary design stage and is high in calculation precision and calculation efficiency.

Description

Technical Field

[0001] This invention relates to the field of crank-rocker mechanism technology, and in particular to a method for analyzing key characteristic parameters of crank-rocker mechanisms based on Catia. Background Technology

[0002] In the field of mechanical transmission, common transmission mechanisms include linkage drives, cam drives, belt drives, chain drives, and gear drives. Linkage drives have outstanding advantages such as high rigidity, high reliability, and strong design adaptability, and are widely used in aerospace, rail vehicles, satellite communications, and other fields. Linkage mechanisms can be classified into four-bar linkages and multi-bar linkages based on the number of links. A clear understanding of hinged four-bar linkages is a prerequisite for studying other multi-bar linkage mechanisms and derivative mechanisms of four-bar linkages (such as double rocker mechanisms, crank-slider mechanisms, and sinusoidal mechanisms).

[0003] Four-bar linkages mostly involve variable acceleration motion, and the transmission ratio cannot be directly obtained from the ratio of the angular velocity of the output component to that of the input component; detailed analysis is required. Taking the crank-rocker mechanism as an example, there are currently two main methods for studying this mechanism. The first method is through geometric analysis, listing the differential equations of motion for all movable links of the mechanism, transforming these equations into matrix equations of displacement, velocity, and acceleration, and solving them in application software such as Matlab. This method is tedious in listing equations and complex in solving, and is suitable for academic research. The second method is to simulate in multibody dynamics software such as Adams and Motion, solving for an approximate solution of the crank-rocker mechanism's motion through modeling, solving, and post-processing. This process requires familiarity with the software, modeling is time-consuming, and post-processing requires writing algebraic equations for the output quantities, making data processing troublesome. Sometimes, it is necessary to output the data and combine it with Matlab or Excel to obtain the desired data curves.

[0004] To address the shortcomings of the two aforementioned calculation methods, this invention proposes a method for rapidly analyzing crank-slider structures within the Catia environment. This method can quickly decompose motion parameters in conceptual or preliminary designs during engineering design, obtaining key indicators and parameters of the mechanism, thus making the design more reasonable and feasible. Summary of the Invention

[0005] The purpose of this invention is to provide a method for analyzing key characteristic parameters of a crank-rocker mechanism based on Catia, so as to solve the above-mentioned technical problems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for analyzing key characteristic parameters of a crank-rocker mechanism based on Catia includes the following steps: Step 1: Determine the instantaneous transmission ratio i of the mechanism based on the three-center theorem; Step 2: Obtain the transmission angle γ and pressure angle α of the mechanism in the Catia sketch interface; Step 3: Further obtain the extreme position angle θ of the mechanism, and calculate the stroke speed coefficient k of the mechanism from the extreme position angle θ.

[0007] Compared with existing technologies, this invention has the following advantages: This invention eliminates the complex process of mathematical modeling and solving the crank-rocker arm mechanism, or the time-consuming and labor-intensive modeling in multibody dynamics simulation software such as Adams, where model modification and iteration are cumbersome. This invention enables rapid iterative calculation in the Catia sketch environment. By modifying the length of different links and the angle of the driving links, the key design parameters of the crank-rocker four-bar linkage can be intuitively displayed. This method can also be similarly extended to multi-link mechanisms and other derivative mechanisms, saving time and effort, providing strong intuitiveness, fast iteration, and rapid output of key parameters. It is perfectly suitable for the preliminary design stage of engineering projects, offering high calculation accuracy and efficiency. Attached Figure Description

[0008] Figure 1 Hinge-crank-rocker mechanism diagram; Figure 2 Transmission ratio diagram of hinge-crank-rocker mechanism; Figure 3 Transmission ratio curve of crank-rocker mechanism; Figure 4 Diagram of pressure angle and transmission angle of crank-rocker mechanism; Figure 5 Extreme position angle diagram of crank-rocker mechanism. Detailed Implementation

[0009] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0010] According to mechanical principles, such as Figure 1 As shown, AD is the frame, AB is the crank, BC is the connecting rod, and CD is the rocker arm. Crank AB is the driving element, which can be driven 360° by a rotary motor or power motor, causing the rocker arm CD to swing within a specific angle range. Rod CD is the load-bearing rod, on which external loads are applied. To calculate the driving torque at hinge A, the transmission ratio of the mechanism must first be calculated.

[0011] According to the "Three Centers Theorem," the instantaneous centers of velocity of links AB and AD are at point A, and the instantaneous centers of velocity of links AD and CD are at point D. Therefore, the instantaneous centers of velocity of links AB and CD lie on the extension of AD, so draw line segment AE. Since the instantaneous centers of velocity of links AB and BC are at point B, and the instantaneous centers of velocity of links BC and CD are at point C, the instantaneous centers of velocity of links AB and CD also lie on the extension of BC, so draw line segment BE. AE and BE intersect at point E, which is the instantaneous center of velocity of the mechanism in this position. At this time, the transmission ratio between the crank and the rocker arm is i = ED / AE. The transmission ratio i changes with the angular displacement of crank AB. If i is too large, the mechanism will occupy a lot of space and weight; if i is too small, the drive motor at point A will require greater torque. Therefore, designing a reasonable transmission ratio i is the core content of this mechanism design. Figure 2 As shown, when the angle between AB and AD is 60°, the instantaneous transmission ratio i = ED / AE = (350 + 88.343) / 88.343 = 4.96. Assuming that the load torque of the CD rod at point D is 100 Nm, then it is only necessary to select a motor with a torque of 100 Nm / 4.96 = 20.2 Nm at point A of the drive rod AB.

[0012] In Catia, by accessing the "Parameters" and "Relationships" options in the structure tree through settings, and parameterizing the ED / AE values ​​in the sketch interface, you can use "Apply Animation to Constraints" to drive the rotation of link AB. This allows you to view the transmission ratio of the mechanism in real time, quickly make engineering decisions, and determine motor selection and link stress. Plotting the driving angle of link AB against the transmission ratio in a Cartesian coordinate system yields the transmission ratio curve, as shown below. Figure 3 As shown.

[0013] like Figure 4 As shown, similarly, draw the extension line CH of rod BC in the Catia sketch interface; with point D as the center and CD as the radius, draw arc CF; draw the tangent CG of arc CF through point C, and draw the perpendicular line CK of CG. This will give the transmission angle γ and pressure angle α of the mechanism at that moment. By parameterizing the transmission angle γ and pressure angle α, their changes can be observed in real time. The transmission angle γ and pressure angle α are complementary angles, and in general design, the transmission angle γ needs to be ≮ 40°.

[0014] like Figure 5 As link AB rotates, there are two positions where link AB and link BC coincide. Specifically, when link AB rotates to position AB1, AB1 and B1C1 coincide; when link AB rotates to position AB2, AB2 and B2C2 coincide. The included angle θ at this point is the extreme position angle of the mechanism. The stroke speed coefficient k of the mechanism can be calculated from the extreme position angle θ: k = (θ + 180°) / (θ - 180°).

[0015] The above describes the method for analyzing key characteristic parameters of crank-rocker mechanisms based on Catia. Through analysis, key design parameters such as instantaneous transmission ratio i, transmission angle γ, pressure angle α, extreme position angle θ, and stroke speed coefficient k can be quickly obtained. These parameters enable designers to quickly judge the rationality and applicability of existing mechanisms in the preliminary design stage of engineering, simplifying the calculation process.

[0016] The above description represents a preferred embodiment of the present invention. For those skilled in the art, any changes, modifications, substitutions, and variations made to the implementation methods without departing from the principles and spirit of the present invention, based on the teachings of the present invention, still fall within the protection scope of the present invention.

Claims

1. A method for analyzing key characteristic parameters of a crank-rocker mechanism based on Catia, characterized in that, The method comprises the following steps: Step 1, obtaining the instantaneous transmission ratio i of the mechanism according to the three-center theorem; Step 2, obtaining the transmission angle γ and the pressure angle α of the mechanism in the Catia sketch interface; Step 3, further obtaining the polar angle θ of the mechanism, and calculating the stroke speed coefficient k of the mechanism according to the polar angle θ.

Images