Grouping Concepts

Given a kinematics assembly, you can trigger the relative motion of a related sub-elements upon kinematic motion. This is achieved through either of two methods: attachment/motion groups or mechanism constraints. The capabilites and characteristics of these methods are described below.

Capabilites
Type DefinitionPrerequisitesAdvantagesDisadvantages
Motion groups
  • Motion groups are a set of devices to be programmed as a single entity to reflect existing controllers, mostly for download
  • Does not require a parent/child relationship
  • Though they are grouped, each entity remains independent in terms of motion (although the program considers them as both)
  • Only one inverse kinematic device per group
  • Requires resource typing
  • Requires attachment and ports (if relative motion is needed)
  • Allows for different motion groups to be created for the same set of devices, allowing different programs on each motion group
  • Allows for coordinated motion programmation
  • Grouped devices are not kinematically solved altogether.
Mechanisms
  • Mechanisms may combine kinematic sub-elements into a single one (so it can be programmed as a single entity)
  • Sub-elements must be parented as children of the main assembly
  • The motion of sub-elements are combined to reflect the mechanism system as an unique entity
  • For flexible assemblies, you must declare the joints to be flexible.
  • Allows for the resolution of a complex kinematics system altogether.
  • Once a mechanism has been defined, it is not meaningful to define another mechanism and combine them for programming.
Note: An attachment is a link between two entities (parent/child) to constrain the motion of the child with respect to the parent. Attachment standalone does not merge or group the entities as a single programmable entity (you must have motion groups as well).
Specific characteristics
Motion groupsMechanisms
Structure Assemblies are not related through parent/child relationshipsAssemblies are related through parent/child relationships
KinematicsGroups are kinematically-independent (only attached)Entities are resolved as a single kinematic entity (even when related through a rigid constraint)
Usage recommendations
Use motion groups when:
  • Resources may come from different suppliers
  • Resources may be interchanged during programming
Use mechanisms when:
  • The combination must be used as a single entity (reuse of multiple instances)
  • The sub-elements don't have a special programming identity
Use an attachment alone when:
  • You need the motion constraints between two elements
Examples
Motion group:





Mechanism:





About Attachments
Attachments define a constrained rigid for simulation link between two entities. Both entities remain kinematically independent.



Attachments can be made between:
  • Two products
  • Two ports, which allows for more control over the relative location. Attachments are not necessarily at the local origin of the attached products.
The recommended approach for attachments is to define ports relative to the axis system, where:
  • Parent: Mount port
  • Child: Base port