Hexapod Technology
Moog FCS is a company managed by engineers and provides engineering solutions for engineers. The unique control loop used by Moog FCS has various benefits over conventional PID or PIDF control loops. Please click on the links below to find out more about Moog FCS's technology.
- Moog FCS Control Loop
- Hexapod Technology
Moog FCS Control Loop
In the late 1970’s Fokker developed a revolutionary control loop, that is based on force control. This was the beginning of a succes story that has lead to the application of this technology in the automotive industry.
Since the early development of the new control philosophy, that was originally developed for flight simulators, much has changed. Not only has the control loop itself matured, it is now also used in the testing industry, for both automotive and aerospace applications.
Unlike traditional control loops, Moog FCS does not use a PID or PIDF controller. A unique feature of the Moog FCS control concept is that it uses an integral force / acceleration and position loop, with the ability to control force / acceleration and position in a simultaneous manner. This allows engineers to easily solve complex control challenges.
This control loop is now available on the smallest 1 to 4 channel controller on the market, the SmarTEST ONE. In itself the best price – perfromance controller on the market, it also features all features of Moog FCS’ larger system sold all over the world.
Hexapod Technology
- Serial and Parallel Mechanisms
- Hexapod
- Hexapods for Automotive Testing
- Force Control with Hexapods
Serial and Parrallel Mechanisms
Serial Mechanisms
- Parallel Mechanisms
A serial structure can be described as a succession of rigid bodies, each of them linked to its predecessor and its successor by a one-degree-of-freedom joint (1 DOF joint).
An example for a serial structure is a classic robot arm or a crane as used at construction sites. Each linkage is connected via a drive or actuator to the next linkage.
Unlike a serial structure, the manipulator (or end-effector) in a parallel structure is connected to all drives (or links). Such a parallel structure is called a “closed loop mechanical chain”. Parallel structures can be found anywhere where high stiffness and low moving mass is required – an example is a modern car suspension system as can be seen below. Iin this case a parallel mechanism of an Audi/VW front suspension. Four beams, steering rack and a vertical spring are used to define the position of the wheel hub in six degrees of freedom.
Hexapod
A Hexapod is a parallel structure where the manipulator or end effector is connected to the base frame (“fixed world”) via six rigid rods. The end points of these rods are attached to the end effector (manipulator) and to the base frame via spherical joints. If the length of the rods can be changed, the end effector can move its position in 6 degrees-of-freedom (6-DOF) relative to the base frame.
This type of structure has been known for a long time. Some theoretical questions linked to this of type structure were mentioned as early as 1645 by Christopher Wren. Around 1800 the mathematician Cauchy studied the rigidity of an “articulated octahedron”. More recently, in 1947, Gough applied the same principle in a machine for testing tyres.
Hexapod for Automotive Testing
The characteristics of the Hexapod parallel structure make them very suited as a tool to produce a 6-DOF force or acceleration for use in automotive testing, for example fatigue testing of car components and/or suspensions. The mechanical structure of the complete system is very simple: Two rigid triangles and 6 identical actuatros.
Each corner of the base frame triangle is connected to the moving triangle with an actuator. The moving platform serves as the end-effector to load forces and/or suspensions on the test specimen. This compact mechanical design reduces facility requirements: the complete system uses less floor space than systems with decoupled kinematics. Inherently a hexapod has large symmetrical excursions for translations and rotations.
Below several advantages of Hexapod systems over existing cascaded systems:
- Simple mechanical structure
- Maximum mechanical and hydraulic stiffness (Adds to controllability and control bandwidth)
- 6 identical actuators
- Full dynamic steering capability
- Unique force / acceleration loop control
- Applicable to half- or complete-axle as well as complete 4 corner vehicle testing
- Dynamic and static suspension characterization capability
- 6 DOF wheel force transducer included
Force Control with Hexapods
The control technology developed and used at Moog FCS allows the operator to control the Hexapod in force, acceleration or displacement control in any Fegree-of-Freedom, separately as well as simultaneously, selectable by the user. The Degrees of Freedom are defined in the frame of reference of the test article, the facility or any other moving or fixed reference frame. Due to the nature of the control loop, the force introduction point can be chosen freely. The use of closed loop force control of the end-effector allows accurate real-time force, acceleration or position control.
The inherent qualities of a Hexapod, together with the Moog FCS innovation to use this device in 6-DOF control loop, leads to a new test system concept which combines traditional fatigue test functions with dynamic suspension characteristics measurement functions.
