The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Sep. 13, 1988
Filed:
Nov. 09, 1987
Alan R Millner, Lexington, MA (US);
Walker Magnetics Group, Inc., Worcester, MA (US);
Abstract
In the magnetic chuck control disclosed herein, the chuck winding is selectively energized in one direction or the other through respective triggerable semiconductor current switching devices. Successively reducing current levels are applied in successive phases of operation, the polarity of the current being reversed in successive phases. During a first portion of each phase the device is triggered to apply a corresponding preselectable voltage. During a second portion of each phase the switching devices are triggered quite late to provide an average voltage which opposes the current flow which was induced during the first portion thereby to quickly reduce the level of current flowing in the winding. The current level is sensed to generate a control signal representative thereof and a sequencing means, responsive to the control signal, operates when the current in the winding falls below a preselected value during the latter portion of each phase thereby to terminate the late energization portion and to initiate the application of current in the reverse direction thereby instituting the next phase in the demagnetizing sequence.