Modular articulated light curtain

Details Modular articulated light curtain Modular articulated light curtain

2000-03-10

2001-10-02

Allen, Stephone B. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

C250S222100, C340S555000

Reexamination Certificate

active

06297498

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to protective devices such as light curtains and more particularly to providing a modular articulated light curtain whose elements may be retained at user selected angles, preferably while retaining light beam resolution through the angles.
BACKGROUND OF THE INVENTION
Light curtains are commonly used to protect hazardous areas from intruding persons or objects. For example, a particular piece of machinery may be dangerous to humans who come too close. By mounting a protective screen of so-called light curtains at the periphery of the danger zone, the presence of an intruding object or portion of a person can be detected. Detection can be used to signal an alarm, turn off the machinery, among other functions.
Light curtains are spaced-apart light emitters and light detectors. Depending upon the application, the spaced-apart distance may range from perhaps 20 cm to perhaps 6 m or more. Absent an intruding object, the light emitting portion of the light curtain emits light that passes through empty space to be detected by the light detecting portion of the curtain. However the presence of an object will block transmission of some of the light, causing the light receiving portion to output a warning signal or command. Typically the lights are turned-on in a series sequence, one at a time.
FIG. 1A
depicts a piece of machinery
10
to whose front edge
20
there is mounted the light receiving unit
30
of a light curtain
40
, and at whose base
50
there is mounted the light emitting unit
60
of light curtain
40
, according to the prior art. As indicated in
FIG. 1A
, the light emitting and light receiving units are coupled to electronics
70
,
80
, not shown here.
The emitted light
90
traverses the region or zone
100
to be protected. If the protected zone is regarded as a plane defined by an array of light emitters and array of light detectors, each array disposed in parallel straight lines, as shown in
FIG. 1A
, standard prior art light curtain devices
40
may be used. However when the protected region
100
involves angles and bends, it is difficult to provide a light curtain without modifying existing components. For example, it typically becomes necessary to stack portions of the light emitters on more than one plane, and to stack portions of the light detecting units on more than one plane. For example, it is desirable to maintain light beam resolution through such angles or bends, yet this design goal is not readily met in the prior art and resolution is degraded in attempting to protect curved or angular regions.
Thus there is a need for a preferably modular articulated light curtain. Preferably such light curtain should maintain light beam spacing throughout, or give the option to intentionally alter beam spacing at desired regions. Such light curtain should permit the user to shape it into desired angles, for example a zig-zag shape, and to retain the light curtain in such configuration to accommodate differently shaped regions to be protected. As noted, light beam spacing should be preserved though the desired angles. Preferably such light curtain should provide modular light emitting units and modular light detecting units, which individual modules are on a single plane, regardless of the angular configuration. As such, one pair of a light emitting module and a light receiving module will preferably be parallel to each other but can tolerate error in planarity, for example ±12°.
The present invention provides such a light curtain.
SUMMARY OF THE INVENTION
In a first embodiment, the present invention provides modules that are joined at a module end with a coupler. A module may be straight, curved, or angled, and will have rounded distal ends, and will include light emitters or light detectors. By contrast, couplers do not include light emitters or light detectors (generically termed herein as light units), can be straight or angled, and have an interior region sized to receive the rounded distal end of an adjacent module. Modules and couplers each include electrical connectors that can matingly engage from a module to a coupler. Within a light emitting module or within a light detecting module, it is preferred that adjacent light emitters or adjacent light detectors, respectively, are spaced-apart from each other with a desired pitch.
As used herein, “light unit” will be understood to refer to a light emitter or to a light detector. Thus a module may generically be considered as having an array of light units spaced-apart from each other a desired pitch. If the light units are light emitters the module is a light emitting module, and if the light units are light detectors, the module will be referred to as a light detecting module. Each module also includes at least one electrical wire or trace coupled to the light emitters or to the light detectors within the module. Couplers maintain electrical continuity between adjacent modules such that electrical signals can be carried across the length of a connected series of modules and couplers. Further, couplers can maintain the desired pitch between adjacent light emitters or adjacent light detectors in adjacent modules. The two distal ends of a series of modules and couplers are terminated with appropriate terminating units. One unit provides electrical termination to the series, will typically not include any light emitters or detectors and can be regarded as a special form of coupler. The other terminating unit brings electrical leads and signals to and from the series, and may include at least one light emitter or detector, and can be regarded as a special form of module.
By way of example, a portion of a light curtain intended to protect two adjacent straight regions having lengths L
1
, L
2
, joined at an angle of &thgr; could be implemented as a first straight module of length L
1
, an angled coupler defining the desired angle &thgr;, and a second module of length L
2
. If, for example, L1 were longer than a standard length module, the L
1
length might be implemented using several shorter length straight modules each having length L
3
, joined together with straight couplers, such that the several L
3
length modules added up to the desired overall length L
1
.
The light curtain is defined by a plane that is itself defined by the locus of the light emitting module(s) and the light emitting coupler(s). It is understood that the light emitting modules are spaced apart but parallel to light detecting module(s), such that the locus of the light emitting modules and the locus of the light detecting module are the same. The spaced-apart distance between light emitting and light receiving modules may, but need not be, vertical in orientation and can vary from perhaps 0.25 M to 30 M or even larger. Non-planarity between a spaced-apart light emitter in a module and a corresponding light detector in a module can be tolerated within limits, for example ±12°.
When detection of emitted light by a corresponding light detector is interrupted, for example by an object intruding in the protected region, an electronic signal carried by the wire or trace in the module/coupler will manifest this interruption. The wire/trace is coupled to conventional electronic drive and detection circuitry that can utilize the signal to identify an intrusion. Such circuitry can, for example, be used to shut down protected machinery, sound an alarm, etc.
An alternative embodiment of the present invention provides modules that pivotably interlock with each other such that a desired angular offset between adjacent modules in the light curtain is readily achieved. As such, the modules interlock directly with each other without requiring an intervening coupler. The modules have rounded distal ends whose radius R≦P
1
/
2
, where P
1
is the pitch of adjacent light units (e.g., light emitters or adjacent light detectors on the module. The distal end to distal end distance L of the modules is (n+1)P
1
, where n is the number of light emitters or light detectors on the modu

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