Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-06-28
2002-05-21
Allen, Stephone (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S221000, C250S239000, C033S366110
Reexamination Certificate
active
06392223
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a tilt sensing device and method for its operation, the device being of the type comprising a) a housing, b) a radiation transmitter and a radiation receiver arranged in or at the housing to form a beam path therebetween, c) a radiation obstructing or deflecting body movable in relation to the beam path and d) a rest surface for the body defining at least two possible rest positions for the body relative the beam path between which rest positions the body can move by gravity at defined tilt angles for the device and which rest positions are selected to give a detectable output difference from the radiation receiver depending on which of the rest positions is occupied by the body.
BACKGROUND
Tilt or inclination sensing or switching devices are known or can be used for a variety of purposes, such as for roll-over alarms in vehicles, level sensors, borehole deviation measuring instruments, patient emergency alarms, car burglar alarms, remote control or manipulation devices, safety switches in hazardous devices etc.
Also a variety of techniques have been employed for detecting the device angular orientation in relation to gravity. Early types relied on a conductive liquid, notably mercury, enclosed in an ampoule with penetrating electrodes. Other detectors based on liquid, as exemplified by U.S. Pat. No. 5,425,179, have been presented but there is a general problems with the presence of liquids in case of failure and among others surface tension and liquid adhesion require a certain minimum size for reliable operation and detection. Another type, as exemplified by U.S. Pat. No. 2,303,360 and U.S. Pat. No. 2,540,974, uses a rolling member movable at certain angles to either press an electrical switch or to bridge a gap in an electrical circuit in order to give a detectable signal. These devices are susceptible to wear, oxidation and contamination and require a minimum size to provide the necessary contact pressure for reliable switching and generally cannot be devised to give a continuous response to inclination angle.
Optical devices with members movable in a beam path between a transmitter and a receiver avoids several of the abovesaid problems. One type, as represented by U.S. Pat. No. 3,097,565, has its movable member suspended as a pendulum in the beam path but is suitable only for small angle deviations and generally requires a liquid dampening of the member. Another type uses an opaque sphere movable over a concave floor centered around the beam axis. Known devices of this type, e.g. U.S. Pat. No. 4,450,353 and GB 2 072 838, are unsuitable for miniaturization and use in portable devices, among others due to the floor design, the necessary large sphere movement, the damping liquid and unreliable response in an upside-down orientation. The U.S. Pat. No. specifications 5,202,559 and 5,030,955 disclose similar tilt responsive devices for use in hand-held remote control applications with multiple channel output. The optical devices described have several features counteracting further improvements, for example by the large lateral sphere movement required, the restriction to digital type output by prepared discrete positions and the reliance on complete optical sealing with certain contact pressure for position detection, all requiring a certain minimum device size.
As known designs are not optimal for use in e.g. truly portable devices, there is a continuing need for small, simple and cheep optical tilt sensing devices which are not restricted to certain tilt conditions, yet have a high and long lasting operating reliability. Several problems arise when trying to push current technology further towards these goals. Miniaturization gives certain reliability problems such as increased sensitivity to impurities. Less space for lateral movements in relation to the beam deteriorates signal to noise ratio. In spite of the limited space, in most portable applications the device has to provide a stable signal in upside-down orientation and furthermore a high degree of reliability is necessary as the devices are frequently used as part of safety systems to prevent hazardous conditions or prevent misuse.
SUMMARY OF THE INVENTION
A principal object of the present invention is to offer a tilt sensing device and a method for its operation obviating the abovestated disadvantages. A more specific object is to offer such a device suitable for use in portable instruments or articles. Another object is to provide such a device of overall small size and low weight. A further object is to provide such a device of reliable long term operation and predictable switching properties. Still another object is to provide such a device requiring but small internal body movements for reliable tilt detection. Yet another object is to offer such a device with reliable operation in upside-down orientation. Still another object is to offer such a device permitting continuous response to tilt angle. A further object is to offer such a device able to be devised for a broad range of tilt angles. Still another object is to provide such a device with the option of a roll orientation independent response.
These objects are reached with a device and a method of the initially stated nature having the characteristics set forth in the appended claims.
While prior art devices generally uses large movable bodies to provide great forces or efficient optical shielding or sealing the current invention utilizes a small body to reach several of the objects outlined. A small body size has proven to be a first prerequisite for reduced overall device dimensions. Within a given space a small body can make a larger relative motion with respect to the beam path, hereby giving a larger detectable signal alteration, which, although advantageous as such, with preference can be utilized to improve on signal to noise ratio and to compensate for less efficient sealing in small devices, hereby allowing for still further size reductions. The movable body, commonly fabricated of heavy material, is potentially destructive to the device interior parts, especially when damping liquids are not present. In fixed or permanent installations this is not a severe problem as the body usually makes small movements relative a rest surface or single discrete jumps at defined angles. In contrast, portable devices typically are turned in every possible direction and are subjected to repeated rough handling including drops and vibrations, under which conditions the body may act to damage its surroundings or at least cause long term deteriorated function from continuous wear and accumulated debris. Movable body size reduction in itself act to strongly reduce these problems as the body weight falls off with third power of linear dimensions and at small body weights and sizes even a surrounding gas medium begin to act as a dampening fluid. Further, when relying on beam path shielding rather than transmitter/receiver window sealing, presence of small amounts of particles are not detrimental to function. Also, when using shielding rather than sealing, proximity of transmitter and receiver becomes increasingly important and a smaller body allows these parts to be further approached, which, contrary to common thinking, compensates for less than complete shielding. According to a preferred embodiment the shielding rather than sealing feature is used to secure point contact, contrary to line or surface contact, between the movable body in its various rest positions and the rest surface, which counteracts adherence, sticking and wedging to thereby maintain free body mobility and controlled switch forces in spite of the small movable body weight. According to another preferred embodiment the transmitter and/or the receiver are equipped with collimator lenses, able to concentrate the beam, which not only improve on shielding performance but also provide protection for the transmitter/receiver and may assist as suitable surfaces of point contact relative the body. Still another preferred embodiment is to use a body of a re
Hjertman Birger
Holte Anders
Allen Stephone
Dinsmore & Shohl LLP
Pharmacia AB
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