# Parallel Mechanism Classification

From the perspective of sports form, parallel mechanisms can be divided into:

• Plane mechanism
• Space agency

Further subdivision can be divided into:

• Plane moving mechanism
• Plane moving rotating mechanism
• Space pure moving mechanism
• Space pure rotating mechanism
• Space mixing motion mechanism

## Classified by the freedom degree of the parallel mechanism

(1) 2 degrees of freedom parallel mechanism.

2 degrees of freedom parallel mechanism, such as 5-R, 3-R-2-P (R is the rotating pair, P is the moving pair).

The planar 5-bar mechanism is the most typical 2-DOF parallel mechanism.

This type of mechanism generally has 2 moving sports.

(2) 3 degrees of freedom parallel mechanism.

3 degrees of freedom parallel mechanism is more various types, the form is more complicated, generally has the following forms:

Planar 3-DOF parallel mechanism, such as 3-RRR mechanism, 3-RPR mechanism.

They have 2 movements and one rotation;

Spherical 3-DOF parallel mechanism, such as 3-RRR spherical mechanism, 3-UPS-1-S spherical mechanism.

The axis of all the motion pairs of the 3-RRR spherical mechanism meets a little space, which is called the center of the mechanism.

The 3-UPS-1-S spherical mechanism uses the center point of S as the center of the mechanism, and the movement of all points on the mechanism is the rotational motion around that point.

3D pure moving mechanisms such as Star Like parallel mechanism, Tsai parallel mechanism and DELTA mechanism.

The kinematics of this type of organization is very simple and positive, and it is a widely used 3D mobile space organization;

Space 3 degrees of freedom parallel mechanism, such as a typical 3-RPS mechanism.

Such institutions are under-ranked institutions, and their different forms of movement at different points in the workspace are their most prominent features.

Due to this special kinematics, it has hindered the wide application of such institutions in practice;

There is also a space mechanism that adds auxiliary members and motion pairs, such as the 3-UPS-1-PU spherical coordinate 3-DOF parallel mechanism used in parallel machine tools developed by the University of Hannover, Germany.

Due to the constraints of the auxiliary lever and the motion pair, the motion platform of the mechanism has 1 movement and 2 rotation movements (also referred to as 3 movements).

(3) 4 degree of freedom parallel mechanism.

Most of the 4-DOF parallel mechanisms are not fully parallel, such as the 2-UPS-1-RRRR mechanism.

The motion platform is connected to the fixed platform through 3 branches, and the two motion chains are the same, each having one Hooke hinge U and one moving pair P.

Where P and 1 R are the drive pairs, so this mechanism is not a fully parallel mechanism.

(4) 5 degrees of freedom parallel mechanism.

The existing 5-DOF parallel mechanism has a complicated structure, such as Lee’s 5-DOF parallel mechanism with a two-layer structure (a combination of two parallel mechanisms).

(5) 6 degree of freedom parallel mechanism.

The 6 degree of freedom parallel mechanism is a large class of parallel robots. It is the parallel research institute with the most researched by domestic and foreign scholars. It is widely used in flight simulators, 6 dimensional force and torque sensors and parallel machine tools.

However, many of these key technologies have not been fully solved, such as their kinematics positive solutions, the establishment of dynamic models, and the accuracy calibration of parallel machine tools.

From a fully parallel perspective, such a mechanism must have six kinematic chains.

However, in the existing parallel mechanism, there are also 6 degree of freedom parallel mechanisms with three kinematic chains, such as 3-PRPS and 3-URS, and a 5-bar mechanism attached to each branch of the three branches. This drive mechanism is a 6 degree of freedom parallel mechanism.

Scroll to Top