What are the types of four-bar linkage mechanisms?

[LeAlaina]

There are three types of four-bar linkage mechanisms: Crank-rocker mechanism: In a hinged four-bar linkage mechanism, if one of the two frame links is a crank and the other is a rocker, this mechanism is called a crank-rocker mechanism. Double-crank mechanism: In a hinged four-bar linkage mechanism, if both frame links are cranks, this mechanism is called a double-crank mechanism. Double-rocker mechanism: In a hinged four-bar linkage mechanism, if both frame links are rockers, this mechanism is called a double-rocker mechanism. Additional information: Hinged four-bar linkage mechanism Theorem 1: In a planar four-bar linkage mechanism, the sum of the lengths of the shortest and longest links is less than or equal to the sum of the lengths of the other two links. Hinged four-bar linkage mechanism Theorem 2: In a hinged four-bar linkage mechanism, if a certain revolute joint can become a full-revolving joint, then among the two components it connects, one must be the shortest link, and the length relationships of the four components must satisfy the link-length sum condition.

[SawyerDella]

There are five common basic types of four-bar linkage mechanisms. The first is called the double-crank mechanism, where both side links can rotate fully, like in the door opening/closing systems of buses. The second is the double-rocker mechanism, where both side links can only swing back and forth, similar to how crane arms operate. The third type, the crank-rocker mechanism, is the most widely used - just like a sewing machine pedal driving the needle, with one crank rotating and the rocker swinging. The fourth type, the crank-slider mechanism, is particularly important in engines, converting the piston's reciprocating motion into the crankshaft's rotation. Lastly, there's the parallelogram mechanism used in train wheel coupling devices, maintaining a parallelogram configuration during motion. Each mechanism achieves completely different mechanical functions by altering the motion forms of the links.

[OJuliet]

There are three basic types based on the frame transformation position. If the frame is taken opposite the shortest link, it forms a double crank, like the driving wheels of a locomotive. When the adjacent link to the shortest is used as the frame, the elliptical machine in fitness equipment applies this crank-rocker principle. When the shortest link itself serves as the frame, it becomes the double-rocker structure of a mixer. In fact, the car wiper is a special case, which amplifies the motion from the rotating motor into a 120-degree sector swing through a four-bar linkage. The transmission mechanism under the baseplate of an old sewing machine is even more ingenious, using a crank-rocker to achieve variable-speed motion of the needle bar. These configuration variants can realize uniform, variable, or intermittent motion.

[BeauRose]

The most intuitive way to observe the degrees of freedom in linkage motion: In a double-crank mechanism, both moving links can rotate 360 degrees, which is the principle used in tractor front-wheel steering. A double-rocker mechanism involves both moving links performing pendulum-like motions, similar to the lifting mechanism of a dump truck bed. The crank-rocker combination is the most widely applied, such as in the reciprocating cutting action of agricultural harvester blades. There's also a special form called the isosceles trapezoid linkage, used in certain car suspensions to maintain wheel alignment parameters. When repairing vehicles, the crank-slider variant is frequently encountered, especially in hydraulic braking systems, where the force transmission from the brake pedal to the booster pump relies on this structure to convert swinging motion into linear advancement.