Material or article handling – Vertically swinging load support
Patent
1996-05-09
2000-09-12
Krizek, Janice L.
Material or article handling
Vertically swinging load support
901 15, B25J 906
Patent
active
061168440
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the field of mechanisms and particularly to mechanisms suited for use in the field of robotics. The described mechanisms are not, however, limited to that field but are suited to applications wherever an article is to be oriented or displaced within a given workspace. The described mechanisms can also be used as sensors to detect both rotational and translational motions.
BACKGROUND TO THE INVENTION
Mechanisms are mechanical structures synthesized with assemblages of joints and links designed to provide them with predictable structural, kinematic and dynamic properties. They are the basis for vast numbers of applications including cars, aircraft, optical instruments, manipulation devices, etc. and as such are particularly important elements of most technological systems.
Mechanisms are synthesized by constraining joints or articulations to fixed relationships by means of links. A kinematic analysis assumes links to be ideally rigid. Most mechanisms can be described by selecting one output link and one ground link and defining the elements there-between.
Parallel mechanisms, a vast sub-class of all mechanisms, offer an opportunity for improved structural properties with rigidity, light weight and improved dynamic properties. Parallel mechanisms used in drives allow actuators to be placed at locations where they contribute the least to an increase of inertia. Further, improved accuracy can be achieved by eliminating the accumulation of errors.
Unfortunately, most known parallel mechanisms with more than two or three degrees of freedom suffer from a reduced usable workspace. The invention reported herein achieves a significant improvement in this area.
If a chain of links and joints forms loops, then the mechanism is termed parallel. If a mechanism requires exact geometrical properties to possess mobility (degrees of freedom), it is termed over-constrained. If a mechanism has no mobility, it is called a `structure`. (The term `structure` may apply to other notions but should be clear by context). If there are no loops the mechanism is called serial.
As joints play a central role in mechanisms and are needed to describe the invention, they are defined herein. The joints needed to describe the invention belong to the class of lower pairs because they can be defined by specifying certain pairs of surfaces which have the property of allowing relative motion without the surface contact being lost. Two surfaces of revolution form the revolute joint which has one angular degree of freedom. Two cylindrical surfaces define the cylindrical joint which has two degrees of freedom, one angular about the axis of the cylinder and one translational along the same axis. Two surfaces shaped as parallel prisms form the prismatic joint which has one freedom of translational motion. The modes of realization of these basic joints include a variety of techniques, e.g. rolling elements of locally deforming members, but these do not change the definition.
A "universal" joint is composed of two non-collinear, preferably orthogonal revolute joints with a center of rotation at the intersection of their axes.
The spherical joint has three degrees of angular freedom of motion. A spherical joint may be composed of spherical surfaces in contact, vis, a ball-in-socket; or can be created by three orthogonal revolute joints with a center of rotation at the intersection of their axes.
A "gimbal" joint has three revolute joints positioned to rotate about a common center of rotation.
Actuated joints are equipped to provide mechanical power derived from an external source. Passive joints are left free to move by virtue of the forces present in the links. Joints may be actuated to provide rotational or translational motion.
Any joint can be instrumented with sensors to measure position or velocity of the relative motion of links. Mechanisms can, therefore, be reversed in their functions. Rather than controlling a driven link through actuators placed at joints, the actuators may be replaced by sen
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"Borrowing Some Ideas From Biological Manipulators to Design an Artificial One"--Vincent Hayward in "Robots and Biological Systems" Nato Series R. Dario (EDS) Springer Verlag pp135-148, 1991.
French David J.
Krizek Janice L.
McGill University
The Canadian Space Agency
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