Glossar

Parallel kinematics: definition, advantages and examples

Nico Nuss 0
KI-generierte Symbolaufnahme: Ingenieur erklärt eine parallelkinematische Hexapod-Plattform [Image content created with AI]

Parallel kinematicsdescribes a robot or machine structure in which several kinematic chains simultaneously guide a moving platform. Unlike a classic robot arm, the joints are not just one behind the other. Several struts or arms connect the fixed base to the moving element and share the task of determining its position and orientation.

What is parallel kinematics?

Parallel kinematics have closed kinematic chains. The movable platform – often called the end effector platform – is connected to the base via several independent chains. Each strand consists of joints, links and, depending on the structure, one or more active drives. All drives must work in coordination so that the platform executes the desired movement.

Typical designs are:Delta robotfor quick pick-and-place tasks as well as hexapods or Stewart platforms, where six adjustable struts can move a platform spatially. Parallel kinematics is therefore not a single type of robot, but rather a design principle with different geometries and degrees of freedom.

How does parallel kinematics differ from serial kinematics?

In serial kinematics, one joint follows the next: the movement of the last link depends on all previous axes. A classic articulated robot is a typical example. With parallel kinematics, however, several paths lead from the base to the platform. This significantly changes the flow of force, stiffness, control and working space.

feature Parallel kinematics Serial kinematics
structure Several closed chains lead a platform. Open chain: joints and links lie one behind the other.
Force and load distribution Loads can be distributed over several strands. Axes that are further out often carry the following links.
Moving mass Drives can be close to the base; that can promote dynamics. Motors and gearboxes move with you depending on the structure.
workspace Often more limited and heavily dependent on geometry. Often more flexibly accessible, depending on the robot arm.
steering Geometry, couplings and singularities require special attention. The chain structure is often more intuitive to model.

The comparison is not a general ranking. Which structure fits better depends on the task, load, acceleration, installation space, required accuracy and safety concept. The basics of the other design are explained in the articleserial kinematics.

Why can parallel kinematics be precise and dynamic?

Several strands support the platform at the same time. This allows the structure to be rigid in suitable work areas and enable high accelerations. In many designs, heavy drives remain at the base while only struts and platform are moved. This reduces the moving mass and can support fast, repeatable movements.

However, these properties do not arise automatically. Joint play, elasticity of the struts, calibration, control, load changes and the specific geometry influence the accuracy that can actually be achieved. Even a precise mechanism requires sensors, appropriate control and validation under real conditions.

The role of degrees of freedom and end effector

Degrees of freedomdescribe which independent movements a platform can perform: displacements along the spatial axes and rotations around these axes. Depending on its design, a hexapod can provide six degrees of freedom. A delta robot, on the other hand, is often designed for fast translational movements and can be supplemented with additional axes.

What the machine actually processes or grips at the end is taken care ofEnd effector. Its mass, cable routing and process forces must be taken into account when designing. More information on how a robot’s movement options are counted can be found in the glossaryDegrees of Freedom (DoF).

Where is parallel kinematics used?

Parallel kinematic systems are used where a clearly defined movement needs to be carried out quickly, stiffly or precisely. Examples are:

  • Pick-and-place in packaging, assembly and food technology, for example with Delta robots
  • Positioning and testing systems
  • Flight simulators and motion platforms
  • Machine tools and machining systems, for example with hexapods or pentapods
  • Specialized medical and optical positioning tasks

Boundaries: Workspace, Collisions and Singularities

Parallel kinematics brings with it design challenges. The struts can get in the way of each other or the environment; The usable work space is therefore often more complex than with a robot arm. There are also singularities: configurations in which small movements or forces can lead to effects that are difficult to control or the platform loses a direction of movement. These areas must already be taken into account in design, path planning and control. For a market-level comparison, the Robotics Atlas provides a structured overview of manufacturers and platforms.

The forward kinematics can also be demanding. While the inverse task – determining the required drive values ​​from a desired platform pose – is often easy to handle for a specific machine, calculating the platform pose from joint stands can require several solutions or numerical effort. That’s why calibration, collision testing and border area monitoring are part of practical operation.

TheFraunhofer IEMdescribes parallel kinematic systems as severalActuators, which guide a platform to precise and fast movements. TheFraunhofer IWUshows the use of the principle in machine tools and explains the connection between low moving mass, speed and acceleration.

Conclusion

Parallel kinematics guides a movable platform over several closed chains. If designed appropriately, it can enable high dynamics and rigidity, but places high demands on geometry, control and safety considerations. For clearly defined, fast or precise movement tasks, it is a strong alternative to serial kinematics – not a blanket replacement.

Frequently asked questions about parallel kinematics

What is parallel kinematics simply explained?

Several mechanical arms or struts move and guide a platform together. They work in parallel instead of as a single chain behind each other.

What is the difference between parallel and serial kinematics?

With serial kinematics, the joints follow an open chain. With parallel kinematics, several closed chains connect the base to a common platform.

What is a Hexapod?

A hexapod is a common parallel kinematic with six adjustable struts that can spatially position and orient a platform.

Why are delta robots so fast?

In many delta robots, the drives remain close to the base. The moving parts can therefore be light, which promotes high accelerations.

Does parallel kinematics have any disadvantages?

Yes. Workspace, collisions and singularities can limit usage. The design and control depend heavily on the respective geometry.

Where is parallel kinematics used?

It is used, among other things, in fast pick-and-place systems, positioning and testing systems, simulators and machine tools.

Bewerte den Beitrag hier!
[Total: 1 Average: 5]
Weitere interessante Beiträge