US5436613A
Expired / Lapsed
US
⏱️ 0.0 years remaining
System for detecting human presence in hazardous situations
Assignee: Institut de Recherche Robert-Sauvé en Santé et en Sécurité du Travail
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Filing: 1993-05-13
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Granted: 1995-07-25
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Expires: 2013-05-13
Abstract
Abstract The disclosure relates to a system for the detection of human presence in hazardous situations near moving machinery; appropriately shaped electrodes are placed in an area to be safeguarded and a radio-frequency signal of appropriate frequency and voltage is applied on the electrodes creating an alternating electric field around them. A bridge circuit is used to measure the capacitive impedance created by the electrodes and a dissipation factor is calculated from the real and imaginary parts of the impedance. If a foreign object is introduced into the electric field, the characteristics of the dielectric are modified creating a change of the value of the dissipation factor. The dissipation of energy in the high frequency region is much greater if this foreign object is a biological tissue as compared to other types of materials, such as conductors or insulators. Thus, the system detects human presence by noting the increase of the dissipation factor above a threshold value, and the movement of the appropriate machine part can then be stopped, thereby eliminating the danger of injury to the person.
Inventors
- 👤 Kalyan Ghosh
- 👤 Tapan K. Bose
- 👤 Raymond Courteau
- 👤 Pierre Gibello
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 01:28
CPC Classifications
G; G08; G08B; G08B13/00; G08B13/22; G08B13/26; F; F16; F16P; F16P3/00; F16P3/12; F16P3/14; F16P3/147; F16P3/148
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
281 words
A system for detecting the human presence in a given area, comprising: an arrangement of at least one electrode located in said area defining a condenser having a capacitance C x , an impedance Z x and a dissipation factor D, whose values depend on the nature of the objects located in said area; means in electrical connection with said arrangement of at least one electrode for applying a radio frequency signal to said arrangement of at least one electrode an alternating electric field around said at least one electrode whereby human presence in said field causes a change of the characteristics of the dielectric of said condenser; impedance bridge means, in electrical connection with said arrangement of at least one electrode, including a known reference impedance Z r , a fixed voltage source S f and a source of adjustable voltage S a ; said sources S f and S a producing a sinusoidal voltage at an operating frequency f op ; said known reference impedance Z r said fixed voltage source S f and said adjustable voltage source S a being in electrical connection with each other and with said arrangement of at least one electrode; vectorial detector means for measuring real and imaginary parts of the complex amplitude of a signal V L between each arms of said bridge: circuit balancing means or continuously adjusting the voltage produced by S a to reduce said real and imaginary parts of V L to zero; means measuring said dissipation factor D from outputs of said vectorial detector means, including means for determining a human presence in said area when a change of said dissipation factor exceeds a predetermined threshold value.
Claim 2
Independent Claim
281 words
A system for detecting the human presence in a given area, comprising: an arrangement of at least one electrode located in said area defining a condenser having a capacitance C x , an impedance Z x and a dissipation factor D, whose values depend on the nature of the objects located in said area; means in electrical connection with said arrangement of at least one electrode for applying a radio frequency signal to said arrangement of at least one electrode an alternating electric field around said at least one electrode whereby human presence in said field causes a change of the characteristics of the dielectric of said condenser; impedance bridge means, in electrical connection with said arrangement of at least one electrode, including a known reference impedance Z r , a fixed voltage source S f and a source of adjustable voltage S a ; said sources S f and S a producing a sinusoidal voltage at an operating frequency f op ; said known reference impedance Z r said fixed voltage source S f and said adjustable voltage source S a being in electrical connection with each other and with said arrangement of at least one electrode; vectorial detector means for measuring real and imaginary parts of the complex amplitude of a signal V L between each arms of said bridge: circuit balancing means or continuously adjusting the voltage produced by S a to reduce said real and imaginary parts of V L to zero; means measuring said dissipation factor D from outputs of said vectorial detector means, including means for determining a human presence in said area when a change of said dissipation factor exceeds a predetermined threshold value.
Claim 3
Dependent Claim
33 words
A system as defined in claim 1, wherein the adjustment of the voltage produced by S a consists of a feedback loop of said balancing circuit means to define the following relationship: ##EQU5##
Claim 4
Dependent Claim
56 words
A system as defined in claim 2, wherein said vectorial detector means comprise vectorial detectors VD 2 and VD 3 to measure V H and V r and wherein said dissipation factor D is calculated using the equation: ##EQU6## where Z' x and Z"x are respectively said real and said imaginary parts of Z x .
Claim 5
Dependent Claim
16 words
A system as defined in claim 3, wherein said bridge is controlled by a digital controller.
Claim 6
Dependent Claim
73 words
A system as defined in claim 1, wherein said at least one electrode is placed near a moving machine component to be guarded and are supplied with radio frequency signals by said impedance bridge through a module of reference impedance containing a reference impedance, said module being in a fixed position relative to said at least one electrode and being connected to said bridge by way of flexible coaxial cables with grounded shields.
Claim 7
Dependent Claim
82 words
A system as defined in claim 1, including a module of reference impedance mounted on a body of a machine, said body being grounded and wherein an electrode on said machine is supplied with a radio frequency signal by said impedance bridge through said module of reference impedance containing a reference impedance and two transformers, said module being in a fixed position relative to said electrode and being connected to said bridge by way of five flexible coaxial cables with grounded shields.
Claim 8
Dependent Claim
30 words
A system as defined in claim 1, wherein said known reference impedance is a capacitor whose value is equal to the capacitance C x of said at least one electrode.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1998-07-24 | 1999-01-23 | 1999-07-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2002-07-24 | 2003-01-23 | 2003-07-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2006-07-24 | 2007-01-23 | 2007-07-25 | $7700.00 | Window Closed / Lapsed |