Patent Application
20090183561
Embodiments are generally related to force sensing devices. Embodiments are also related to load measuring pins and components thereof.
Load measuring pins can be utilized to measure load and force and provide overload protection. The pins can be mounted into machines in place of normal shafts and can be fitted with strain gauges, allowing them to produce a signal proportional to the measured load. Load measuring pins is typically an electronic device or transducer that can be utilized to convert a force into an electrical signal. Load measuring pins are designed for many diverse applications as direct replacements for clevis or pivot pins. Such components can be typically employed in the context of rope, chain and brake anchors, sheaves, shackles, bearing blocks, pivots and other similar devices.
Load measuring pins operate based on a shearing principle. That is, the deformation of the load-measuring pin proportional to a load can be measured through a strain gage bridge integrated in the load pin. The load pin includes a relatively massive constraint, which functions as rigid members for directing the force to be measured to the strain gage bridge while remaining substantially unaffected by extraneous forces. The constraints should be independent of typical extraneous forces that are not desired as measured quantities.
When force is applied to the load-measuring pin along its sensitive axis, the effect on the strain gage bridge results in an output signal proportional to the applied force. The powering of the strain gage bridge, as well as the amplification of its output signal voltage, can be performed either by an external amplifier or through an internal amplifier. The amplifier allows monitoring of several levels depending on the execution.
The majority of prior art load measuring pins can be designed with external grooves that can be machined into the outer circumference of the load pin. Such external grooves are required to provide separation between the loading surfaces and the constraint surfaces and to minimize bending stresses, which cause inherent non-linearity. These external grooves are susceptible to corrosion and hydrogen damage from plating operations, which are required to generate the bearing surface necessary in an aircraft breaking system. Similarly, the load pins does not provide an independently loaded constraint locations and a smooth internal bore for associating the strain gages. These factors affect the performance of the load-measuring pin.
Based on the foregoing it is believed that a need exists for an improved load-measuring pin as disclosed in further detail herein.
The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is, therefore, one aspect of the present invention to provide for an improved force sensing apparatus.
It is another aspect of the present invention to provide for an improved load-measuring pin for the creation of independent load locations.
It is further aspect of the present invention to provide for an improved load-measuring pin with smooth internal bore.
The aforementioned aspects and other objectives and advantages can now be achieved as described herein. A load pin brake cell apparatus includes a load pin element that can be machined with a pair of external grooves in order to create independent load locations. A sleeve can be installed over the load pin element and can be welded at each edge of the grooves in order to relocate the pair of grooves to the interior of the load pin element. The sleeve and the load pin element act as one homogenous piece and ensure predictable and total transfer of stress and strain to a strain gage location inside the load pin. The ratio of cross sectional area between the sleeve and the load pin can be maintained at a minimum in order to minimize the non-linearity due to bending stresses. The sleeve wall can be thick enough to prevent yielding at the grooves.
The load pin element can be machined to form a smooth internal bore which includes the strain gage location associated with one or more strain gages that can be protected against physical damage, moisture and contaminants. The strain gage undergoes a change in resistance proportional to deflection of the load locations and therefore proportional to the load applied to the independent load locations. A Wheatstone bridge or other resistance-measuring device can be connected to the strain gage in order to accurately indicate the load on the load pin element. A cooperating connector can be utilized for coupling the strain gages to electrical circuitry for indicating shear force.
The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein.
The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof.
Referring to
The grooves 120 and 125 can be machined in a root of the load pin element 100 in order to minimize stress concentration at the grooves 120 and 125, which in turn reduces peak stress at the grooves 120 and 125. The locations and shapes of the grooves 120 and 125 depicted in
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The central internal bore 150 includes a cooperating connector 190 which can be utilized for coupling the strain gages 160 and 165 to electrical circuitry for indicating shear force. As the strain gages 160 and 165 and connector 190 of the load pin element 100 is totally contained within the small central internal bore 150, the load pin brake cell apparatus 200 is inherently waterproof. The sleeve 140 and the load pin element 100 together can form a single homogeneous component in order to ensure predictable and total transfer of stress and strain to the strain gages 160 and 165 inside the load pin apparatus 200.
The strain gages such as gages 160 and 165 can be symmetrically arranged about the minimum depth point at a central vertical plane of the load pin element 100. The strain gages 160 and 165 can also be bonded to the surface of the smooth central internal bore 150 in a conventional manner, as will be understood by those skilled in the art. The curved shape of central internal bore 150 facilitates placement of the strain gages 160 and 165 at the point of maximum stress and also provides maximum stiffness for a given level of sensitivity. A load can be applied to the independent load locations 130, 132 and 134 of the load pin element 100 which bend in an amount proportional to the load, within a limited range of loading. The bending effect on the strain gages 160 and 165 results in an output signal proportional to the applied force. The strain gages 160 and 165 are of the common type, which undergoes a change in resistance proportional to its elongation or compression.
A Wheatstone bridge or other accurate resistance-measuring device can be connected to the strain gages 160 and 165 to measure the change in resistance, all in a well known manner, to measure deflection and therefore to indicate the amount of load on the load locations 130, 132 and 134. The powering of the strain gages 160 and 165 as well as the amplification of the output signal voltage, can be performed by an amplifier (not shown). As will be understood by those skilled in the art, the placement of central internal bore 150 midway between upper body 110 and the lower body 115 results in the isolation of the central internal bore 150 from certain of the extraneous forces and moments. Other residual or extraneous forces can be cancelled out by the Wheatstone bridge arrangement of the strain gages 160 and 165. The internal grooves 120 and 125 and the strain gages 160 and 165 can be protected by the sleeve 140 against physical damage, moisture and contaminants.
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It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
