Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-09-17
2002-07-16
Hofsass, Jeffery (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S680000, C192S12900A
Reexamination Certificate
active
06420974
ABSTRACT:
FIELD OF INVENTION
The present invention is related to a safety control system for a machine-guarding application. In particular, the present invention relates to a control system for a safety switching mat configuration.
BACKGROUND OF THE INVENTION
Industry is making increasing use of machines to assist in performing dangerous or repetitious tasks. Many of these machines, or the environments in which they operate, are hazardous to humans because of large moving parts, extreme operating temperatures, dangerous chemicals, and other hazards. Therefore, more attention is being focused toward workplace safety issues, such as systems and methods for guarding machines.
Independent Third Party Standards Organizations, such as the European Machine Directive, Occupational Safety and Health Administration (OSHA), and American National Standards Institute (ANSI) have promulgated standards for machine guarding. As part of these standards, machine safety solutions are often required to be “control reliable.” ANSI defines control reliability as “a method of ensuring the integrity performance of control systems, including guards and safeguarding devices that interface with the control system.” OSHA similarly requires that “machine controls should be designed and constructed so a failure within the system does not prevent normal stopping action . . . when required, but does prevent initiation of a successive stroke until the failure is corrected.”
While progress is being made toward implementing machine safety systems, much of the focus has been on the mechanisms for sensing the presence of objects, such as humans. For example, door sensors, laser-based intrusion sensors, and pressure-sensitive mats are known by those having skill in the machine safety field. However, there exists a need to provide a reliable and flexible control system for interfacing the sensing systems with the machine or machine controller. There also exists a need for a control system that can be used to implement a control reliable machine safety solution.
SUMMARY OF THE INVENTION
In accordance with an illustrative embodiment of the present invention, some of the problems associated with safety in machine environments are addressed.
A control system is provided for use in a machine-guarding application. An exemplary embodiment of the control system includes pressure-sensitive devices producing a disable signal and a quantity indication signal, a quantity selector for setting a specified quantity of pressure-sensitive devices, a comparator for generating a status signal responsive to the quantity selector and the quantity indication signal, and an activation module coupled to the pressure-sensitive devices and the comparator. The activation module is operative to produce an output switching signal that disables power to a machine in response to the disable signal or the status signal.
A second embodiment of a control system for use with a plurality of safety mats in a machine-guarding application includes first and second bias voltages, switches corresponding to the safety mats that produce a disable signal when at least one of the switches is in a closed state; a mat-quantity selector for setting a specified quantity of safety mats, and a mat-quantity comparator producing a status signal responsive to the specified quantity of safety mats differing from an actual quantity of safety mats. An activation module produces an output switching signal responsive to the disable signal or the status signal, to disable power to a machine.
In another aspect, the control system includes a redundant mat-quantity comparator connected to the mat-quantity selector and the safety mats for producing a redundant status signal responsive to the specified quantity of safety mats differing from the actual quantity of safety mats. A redundant activation module then produces a redundant output switching signal responsive to the disable signal or the redundant status signal.
In a third embodiment, a control system for use in a machine-guarding application is provided, having pressure-sensitive safety mats with conductive plates, a quantity selector for setting a total specified impedance, a first window comparator producing a first status signal responsive to a first input voltage being outside a voltage window, a first optical coupler producing a first disable signal responsive to a first threshold current, and a first activation module producing a first output switching signal responsive to the first disable signal and the first status signal.
An alternative exemplary embodiment includes a second window comparator and a second activation module having a second optical coupler.
The foregoing and other features and advantages of preferred embodiments of the present invention will be more readily apparent from the following detailed description, which proceeds with references to the accompanying drawings.
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IDEA 1401-A Controller Brochure, Date Unknown (5 pages).
Pinnacle Systems, Inc. STTS Installation Manual, Rev: May 1996. (11 pages).
Scientific Technologies Inc. SMC-1 Series—Din Rail Version, Rev: D, Date Unknown (8 pages).
Baker Andrew Dexter
Travassos Luis Filipe
Abeyta Andrew A.
Hofsass Jeffery
Honeywell Data Instruments Inc.
Huang Sihong
Thymian Marcus J.
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