Measuring and testing – Instrument proving or calibrating – Speed – velocity – or acceleration
Reexamination Certificate
1998-10-02
2002-05-21
Williams, Hezron (Department: 2856)
Measuring and testing
Instrument proving or calibrating
Speed, velocity, or acceleration
Reexamination Certificate
active
06389875
ABSTRACT:
THE FIELD OF THE INVENTION
This invention relates to the testing for faulty, therefore dangerous, performance of various types of zero speed indicators that are used to prevent a machine guard from being opened until the machine has come to a complete stop or has slowed sufficiently to prevent injury to anyone intending to access or work on the machine in the guarded space. The testing methods, devices, processes and decisions on test outcomes, are constructed and arranged so that the indicators can be tested while the machine is running, preventing unnecessary production interruptions and machine shutdowns, as well as take advantage of scheduled and unscheduled machine shutdowns to perform the tests. By performing these tests the hazardous opening of a guard due to a faulty zero speed indication can thus be anticipated and prevented.
For additional safety, machine guard protective systems will sometimes utilize motion interference or blocking devices which are inserted in the motion path of a component of the stopped machine so that machine motion cannot take place while the guard is open. The present invention further relates to the testing of the insertion of motion interference or blocking devices in conjunction with zero speed indicators, both of which must perform correctly in order to permit the unlocking and opening of the guard.
BACKGROUND OF THE INVENTION
Barrier guards, shields, covers, screens and the like are among the oldest known safeguards for protecting personnel from the hazards of moving machinery. Their effectiveness derives from three properties: they prevent entry of the body into the zone of operation, they retain expelled missiles, and they define the safe from the unsafe portions of the machine. The need to access machinery leads to the removal or openings of barriers whereupon their concomitant protection is lost. Heretofore the shortcomings have been addressed by interlocks, which provide a connection between a barrier and the control or power system of the machinery to which the barrier is fitted. The interlock and the barrier with which it operates is designed, installed and adjusted so that until the barrier guard is closed into its protective state the interlock prevents the machinery from operating by interrupting the power medium and also so that opening of the barrier causes the hazard to be eliminated before access is possible or it may be necessary that the barrier remain closed and locked until the risk of injury from the hazard has passed.
The barrier locking system wherein the barrier is to remain locked until the risk of injury from the hazard has passed is necessary when either 1) simply opening or removing the guard does not eliminate the hazard before access is possible or 2) opening a guard other than at predetermined points in the machine cycle may expose the hazard.
The guard locking system will normally consist of a timing device or motion or position sensing device and a guard locking device. These may be individual units or combined in one assembly. Variable conditions of operation of machinery produce variable amounts of run down and in these circumstances a timing device may be inappropriate to determine when the run down has reached a non-hazardous state since it has to be set for the longest run down time that might be expected. The variable time element may, however, be eliminated by the use of a motion or position sensing device, which allows the guard to be opened as soon as the hazard is no longer present.
Available on the market today are a number of position, motion, timing and guard locking devices that operate on various principles. Among motion and position sensing devices some may suffer from the disadvantage that they show poor response at low speed and are therefore acceptable only where residual motion after the guard has been opened could not cause injury. On the other hand, where injury could result from residual motion, more sensitive devices and or timing devices may be necessary. Examples of typical motion or position sensing devices are a) rotation sensing devices that may operate on centrifugal force, friction , eddy current generation, voltage generation, optical or electronic pulse generation b) photo-electric beam c) proximity devices or d) position switches or valves.
Timing device examples include a) mechanical electrical or electronic clocks b) delay relays c) sequence valves d) threaded bolt or e) a dashpot.
Examples of typical guard locking devices are a) a captive-key unit b) a trapped-key unit c) mechanical bolt or d) shotbolts which may be solenoid operated, hydraulic or pneumatic.
The present invention relates to the testing of motion sensing devices that indicate zero speed or the cessation of motion. These devices actively monitor moving machine elements and are never benign when the machine is active. Such indicating devices may wear out or get out o f adjustment or otherwise fail by prematurely signaling that motion has been arrested. This leads to unlatching of the barrier guards before the motion has ceased and before entry to the protected regions is safe. A statistically significant number of people will depend on the efficacy of the motion detectors to unlock guards when it may not be safe to do so.
To help prevent a false sense of security, it is desirable to improve the reliability of motion detectors and reliance thereon by regularly testing them. The dependence on zero speed systems is entirely analogous to the public's reliance on the “safety edges” on ordinary elevator doors.
Zero speed indicators may be completely removed from machines and tested by methods specified by the manufacturers. This procedure is practical only when infrequent inspections are anticipated and when the safety of the basic machine is not compromised by the removal of the motion indicator such as during a general machine shutdown.
The present invention describes a process whereby the motion detectors are frequently and automatically tested in situ while the machinery is in motion (and production) and while total personnel protection is assured. A further novel process is envisioned where the motion detectors are automatically tested in situ whenever the machine is shut down, such as when control systems stop switches are activated for lunch breaks, routine cleaning, maintenance or end-of-shift, when emergency stop devices are employed, when power disconnect is effected; or when latchless interlocked barriers are opened. In addition, when the motion detector indicates that the moving parts have stopped, it may be desired that absolute safety he insured by requiring a motion blocking member to be insertable and inserted between the now stopped moving parts before a guard protecting such parts can be opened.
SUMMARY OF THE INVENTION
There are many applications of safety closures or barriers that must remain closed and locked until the dangerous components that are guarded come to a stop. In such situations it is usual to employ run down completion detection devices such as motion detectors, zero speed switches indicators or detectors, timing devices, delay devices, interference devices, and motion blockers to make a final check to determine that the machine has in fact come to the required stop.
The present invention is directed to the testing of zero speed indicators and the incorporation of interference or motion blocking devices into the overall testing process of guard closures whether such closures are used separately from or in conjunction with interlocks, closure locks, zero speed indicators, and various testing devices. The testing, methods of testing, testing process, testing systems and devices for interlocks, guard closures and closure locks have been extensively detailed in two patent applications filed in the names of the two inventors of the present invention. These applications are incorporated by reference into the present application and set forth in detail the testing, methods of testing, testing processes testing systems and devices for interlocks, guard closures and closure locks. O
Barnett Ralph L.
Liber Theodore
Fayyaz Nashmiya
Williams Hezron
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