Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-02-18
2001-03-20
Lee, Benjamin C. (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S572100, C073S761000, C073S779000, C073S780000, C411S014000, C331S065000, C336S200000, C356S370000, C356S389000, C250S559190, C250S559270
Reexamination Certificate
active
06204771
ABSTRACT:
BACKGROUND OF THE INVENTION AND PRIOR ART
1. Field of the Invention
This invention relates to load indicating fastener systems that are adapted to indicate loads to which they are subjected and, more specifically, to a non-contact electronic device, such as a reactance capacitor, which measures a changing air gap or form produced when a fastening system is strained, and, more specifically, to a non-contact image processing or laser device, which measures a changing air gap or form produced when a fastening system is strained.
2. Description of the Related Art
It is desirable that applied fasteners systems should be accurately tightened to the designed load levels in order to ensure the structural integrity of the bolted joint. It is well known that indicating strain gives a true representation of the load induced in the fastener systems. Torque wrenches are commonly used for tightening fasteners to predetermined torque levels, but they are subject to unpredictable friction so that the strain produced can be widely inaccurate. In other words, controlling torque will not lead to accurate loading of a fastener system.
Prior Contact-Type Fastener Extension Measuring Devices
Some measuring devices, for instance linear transducers, need to make physical contact to be functional. These contact methods are inherently difficult to use in the field. The measurements of strain are extremely small and any surface contamination (corrosion, dirt, natural abrasives, in service damage, etc.) leads to significant errors. Accordingly, it is an object of the present invention to measure strain by using a non-contact device and method.
Prior Non-Contact-Type Fastener Extension Measuring Devices And Methods
Previous non-contact-type devices and methods of measuring the extension of a fastener under strain have utilized electrical components within each individual fastener, typically a bolt or a stud. These earlier methods have a number of significant problems associated with them.
One problem with previous non-contacting measuring devices is that it is prohibitively expensive to instrument each individual fastener with electrical components. Additionally, the integrated instrumentation compromises the integrity of the fastener and is not suitable for the rugged environments of many applications. Accordingly It is an object of the present invention is to provide a cost effective load indicating fastener in which the fastener itself carries no electric parts.
A further problem with previous non-contacting measuring devices is that they typically require complex modification of the fastener making the manufacturing process difficult. Accordingly, it is an object of the present invention to measure the fastener extension using a simple device and method which require only a slight modification to the fastener system which is readily and easily incorporated during the manufacturing process.
BRIEF SUMMARY OF THE INVENTION
Set forth below is a brief summary of the invention which achieves the foregoing and other objects and provides the foregoing and hereafter stated benefits and advantages in accordance with the structure, function and results of the present invention as embodied and broadly described herein. Applicant's invention includes independently both the apparatus and the methods described herein which achieve the objects and benefits of the present invention. Both formats of the invention are described below, and it is applicants intention to claim both formats even though from time to time below for purposes of clarity and brevity applicant will use either one or the other format to describe various aspects and features of the invention.
According to the present invention a load indicating fastener system is provided which comprises a body to which strain is applied when the fastener is in use, a load sensing means having parts arranged for relative movement in response to change in length or form of the body or an associated washer design under an applied strain, and a separate non-contact gap measuring device, such as an electronic device including a reactance capacitor, or such as an image processing device, or such as a laser device, (hereinafter collectively and/or separately referred to as “a non-contact gap measuring device”) which, when secured adjacent to the fastener, registers the said relative movement of the moving parts by a non-contact method.
The fastener system may be in the form of a bolt or stud, a nut and washers, or it may take other forms. In the form of a bolt, the body of the fastener comprises a head and shank which may be of substantially standard form. Similarly, in the form of a stud, the body comprises a shank which may be of substantially standard form. In either of said forms, a washer may incorporate the means of indicating the moving parts being sensed by a separate non-contact gap measuring device of the type described above. In the case of bolt or stud, the load-sensing element responds to a change in length of the shank under the applied strain. In the case of the washer, the load sensing element senses the change of shape in the form of the washer under applied strain. Conveniently, the gap measuring device can be secured at the bolt head, thread end, stud end, or washer where it can easily be secured when the fastener system is in use.
The load-sensing element indicates changes in the length of the body of the fastener, or changes in the form of the washer, or changes in the form of the bolt head as the fastener system is being secured and when the fastener system has been secured. Thus, as the fastener system is being secured, the applied loads will be registered by the non-contact gap measuring device which will indicate when the fastener system reaches a required working load. The non-contact gap measuring device can be attached to the fastener system and obtain a measurement which can be displayed on a computer monitor
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or other display unit. This measurement can be used during the tightening process. The measurement can be used after the initial tightening to inspect for any changes in the initial strain condition.
Actual fastener system loads may be indicated on the monitor
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and an electrical output can be used to control power tightening tools (not shown) or indicate a warning when the fastener system desired load has been achieved.
The load sensing means may be arranged to register applied loads up to the fastener system material proof loads, (proof load is the maximum load that can be sustained before there is a permanent change from its original dimensions.)
The creation of a gap that changes with changing strain can be achieved in various ways. In the preferred embodiment the means to create this changing gap comprise a load-sensing element disposed in the direction in which strain is applied to the body when the fastener system is in use, and has an anchorage part. The anchorage part is rigidly anchored to the body at a part of the body in which there is movement when the fastener is applied for use. An air gap between the non-contact gap measuring device and the element widens or reduces depending on whether the fastener is being secured or looses strain. The non-contact gap measuring device reacts by measuring the air gap and registers the applied load on a monitor
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. Preferably the load-sensing element is made of the same material, or at least has the same coefficient of thermal expansion, as the material of the body. This way, changing temperatures at which the fastener system may be used will not affect the functioning of the load-sensing element.
In a preferred embodiment the load-sensing element is a solid diameter bar, one end providing the anchorage part, the other free end to move relative to the fastener. At least part of the load sensing element may be located in a blind bore or passage in the body. When the load sensing means comprises an element, as described above, it may be provided by an insert fitted into the blind end portion of the bore or passage. The anchorage may be anchored into the base of the bore or p
Clarke Ronald C.
Lee Benjamin C.
Lisa Donald J.
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