Electromagnetic gripping arrangement for metallic workpieces

An arrangement for gripping metallic workpieces formed of ferromagnetic materials or electrically highly conductive materials, by means of electromagnetic forcs. In one embodimet, two linear-motor stators perform as gripping elements by producing travelling fields which exert gripping forces on the workpieces. The linear-motor stators may be configured to conform to the geometry of the workpieces, and are supported by at least one gripper arm.

BACKGROUND OF THE INVENTION 
This invention relates generally to arrangements for gripping metallic 
workpieces, and more particularly, to a system which utilizes 
electromagnetic forces to grip workpieces formed of ferromagnetic or 
electrically highly conductive materials. 
It is a problem with automated manufacturing systems that there has not 
existed a universal gripping arrangement for handling a variety of 
materials and product configurations. This problem is particularly acute 
in automated manufacturing systems which are used to produce small and 
medium-size production runs of products, where it is not economically 
feasible to provide customized grippers. 
In addition to mechanically operated grippers, other types of gripping 
arrangements are known, such as vacuum suction grippers, and 
permanent-magnet or electromagnetic grippers. All of these grippers have 
serious drawbacks. Mechanical gripping arrangements must customarily be 
adapted to the workpiece, vacuum grippers impose stringent requirements 
upon the surface quality of the workpiece, and magnetic grippers can be 
used only for ferromagnetic workpieces. 
It is, therefore, an object of this invention to provide an electromagnetic 
gripping arrangement which can be utilized for handling ferromagnetic 
materials, such as iron, cobalt, or nickel; and electrically highly 
conductive materials, such as copper and aluminum. 
SUMMARY OF THE INVENTION 
The foregoing and other objects are achieved by this invention which 
provides a gripping arrangement which utilizes electromagnetic circuits 
for generating travelling fields for exerting gripping forces. 
In one embodiment of the invention, the stators of linear motors are 
utilized as the electromagnetic circuits. Such stators may be 
advantageously adapted to conform to the geometry of the workpieces. 
It is a feature of the invention that gripping of the workpieces is 
achieved by means of volume forces which permit versatility with respect 
to the geometry of a workpiece, and the material from which it is formed.

DETAILED DESCRIPTION 
FIG. 1, which consists of FIGS. 1a, 1b and 1c, shows a gripping arrangement 
formed with two linear-motor stators arranged at right angles to one 
another. In FIG. 1a, a cylindrical workpiece 12 of ferromagnetic material, 
such as iron, cobalt or nickel, or of an electrically highly conductive 
material, such as copper or aluminum, is gripped by two linear-motor 
stators 11 which are shown to be arranged at 90.degree. with respect to 
one another. Linear-motor stators 11 form the electromagnetic circuitry 
which generates travelling fields in the direction of arrows 16 and 17. 
The travelling fields produce the required gripping forces. 
The gripping of workpieces which are formed of electrically highly 
conductive material is achieved by electrically inducing eddy currents in 
the material. The linear-motor stators and the grip workpiece are 
supported by a gripper arm 15, which is only schematically shown in the 
drawing. 
FIG. 1b shows the orthogonally arranged linear-motor stators 11 gripping a 
rectangularly shaped workpiece 13. The travelling electromagnetic fields 
which are generated by linear-motor stators 11 are propagated in the 
directions of arrows 16 and 17. 
FIG. 1c shows orthogonal linear-motor stators 11 gripping a rectangular 
workpiece 14. As previously noted, the travelling fields are propagated in 
the directions of arrows 16 and 17, and the structure is supported by a 
gripping arm 15, which is shown schematically in the figures. 
FIG. 2 shows linear-motor stators 21 arranged parallel to one another. The 
linear-motor stators are coupled to each other by a stop 23, and are shown 
gripping a slab 22. The structure shown in this figure is supported by a 
gripper arm 24 which is only schematically represented. Gripping is 
achieved by the production of travelling fields which are propagated in 
the directions of arrows 25 and 26. 
FIG. 3 shows a pair of curved stators 31, each having the cross section of 
a quarter of a cylinder. The curved stators are shown gripping a 
cylindrical workpiece 32 by the production of travelling fields which are 
propagated in the directions of arrows 34 and 35. A gripper arm 33, which 
is only schematically illustrated in the figure, supports the curved 
stators and the gripped workpiece. 
Although the invention has been described in terms of specific embodiments 
and applications, other embodiments and applications will be apparent, in 
light of this teaching, to persons skilled in the pertinent art. For 
example, it is to be understood that the gripping performance of the 
stators is improved if their geometry is configured to conform to that of 
the workpieces. The drawings and descriptions in this disclosure are 
merely illustrative of the principles of the invention and should not be 
construed to limit the scope thereof.