Synthesis of Linkage Mechanisms

Linkage synthesis is the process of designing a linkage mechanism to achieve a desired motion or path. It involves identifying the type of linkage, the desired position of the links, and the length and arrangement of the links. The goal is to create a mechanism that is efficient, accurate, and reliable. It is usually the first step when designing a machine where motion or work is accomplished with a linkage mechanism.

The desired position of the links is determined by the specific task that the linkage mechanism is designed to perform. For example, a linkage mechanism that is used to move a robotic arm will have different position requirements than a linkage mechanism that is used to open and close a door. For spatial mechanisms, the synthesis involves using Inverse kinematics to identify what angles of control and link lengths can achieve desired positions. Additionally, a concept call path planning is important to avoid collision with other objects. Spatial mechanisms and control are a key topic in robotics. For planar mechanisms, graphical and analytical techniques can be used to synthesis a mechanism.

A secondary goal for synthesis is ensuring the desired type of mechanism actuate is possible. The type of actuator that is used to drive the linkage mechanism depends on the specific requirements of the application. Continuous rotating motors (DC, AC, and stepper motors as an example) are commonly used for applications where the mechanism is Grashof and the driving link can fully rotate. Servos are used for applications where partial rotations are required (often non-Grashof). Linear actuators are used for applications where linear motion is required.

General Synthesis Process

The process of planar mechanism synthesis usually involves the following steps:

1. Identify the path or location for a link or part of a link. For example, a grasping component attached to a coupler must move a product on a manufacturing line from one machine to another. The exact location of the desired positions is needed to determine link lengths and grounding locations.
2. Make design choices for ground location based on the positions or path constraints. Any four-bar mechanism can be solved as a system of equations based on ground locations and link positions. Therefore, the design freedom to choose where the linkage will be grounded depends on how completely the path must be planned. For example, in “two-position synthesis,” there are an infinite number of places along two lines where the ground link can be located, while “three-position synthesis” fully constrains the ground locations to two precise points.
3. Determine the link lengths and ground locations. Once the link lengths and ground locations are determined, the mechanism is defined. Analysis is then needed to ensure that the mechanism moves as desired, to determine what type of actuation is needed to achieve the desired motion, and to define the shape of the links to avoid interference and meet any performance goals. Recall that links can have any desired shape as long as the distance between nodes stays the same. The linkage will have the same kinematic performance regardless of the shape of the links.