A reflection-type photoelectric proximity detector and switch is capable of detecting the incremental and binary proximity of a finger through several layers of glass, cancelling out extraneous reflections and stray sources of radiation.
The circuitry includes a modulated infrared emitter, an infrared detector, an optical barrier, an infrared filter, a bandpass filter, a signal rectifier, a biasing circuit to remove unwanted detected modulated signal, an amplifier, an incremental proximity output, a comparator, a detection reference, and a binary proximity detect output.
In one embodiment a multitude of photoelectric proximity switches are installed on the inside of a store window, detect finger proximity from outside the window, and control electric appliances inside the store window. From outside the window, a user can select what is displayed inside the window.
This design relates to proximity detectors and switches, and in one embodiment it is concerned with a touch detector for mounting inside a store window, enabling a user outside the window to control appliances and/or displays inside the store.
A number of different types of proximity detectors and switches have been in use or disclosed. Switch panels that use the reflection of infrared radiation to detect finger touch are disclosed in Sauer's U.S. Pat. No. 4,340,813. Short range reflective controls such as Micro Switch (a division of Honeywell) Model FE7B use the reflection of modulated infrared radiation to detect objects.
Fukuyama et al. U.S. Pat. No. 4,306,147 discloses a reflection-type photoelectric switching apparatus which detects the presence of an object in a mechanically adjustable sensing area. Aromat (a member of Matsushita Group) Model MQ-W3A-DC12-24V photoelectric sensor detects the presence of an object in an electrically adjustable sensing area using optical triangulation.
Philipp U.S. Pat. No. 4,879,461 discloses a reflective-type detection system which senses the presence of an object against a background using a general technique of nulling to negate the effects of stray (e.g. ambient) light by adding the complement of the detected signal to a summing point in the circuit to cancel the signal generated by stray light.
In a system using a modulated emitter, this requires the generation of an amplitude and phase regulated modulated signal as a complementing signal. As explained below in the present system a filtered and rectified version of a detected signal is nulled with a constant (DC) level signal.
Reflecting-type infrared switches use the reflection of infrared light off an object to detect the presence of the object. Such sensors are in common use in industry to detect the presence of an object without having mechanical contact with the object, leaving the object undisturbed. These sensors lack mechanical contacts which wear and soil, giving them long lifetimes.
Reflective-type infrared switches have the potential to detect finger proximity through glass. A preferred application of a reflecting-type infrared switch is a touch switch that allows the control of electric devices located inside a store window from outside. Locating all system components inside the store window affords them safety from the elements of weather and vandals and eliminates the need to drill through building walls and glass. The operation of electric devices could occur during or after store hours.
Detecting finger proximity through one or more glass panes that might include air gaps in an environment that can include a multitude of radiation sources and reflections increases the difficulty of the task. Reflective-type infrared switches that use modulated emitters and infrared and electronic filters minimize the effect of extraneous radiation outside the bandwidth of the infrared and modulation frequencies. Extraneous radiation sources would include sunlight, artificial window and street lighting, and automobile headlights.
A common detection practice used to detect the presence of an object with a reflecting-type infrared switch using a modulated emitter is to optically and electronically filter the reflected signal and compare it to a threshold which is applied against a composite signal which may include reflections from other objects in the sensing region.
This technique does not take into account the presence and effect of large extraneous reflections which can occur in the preferred window application described above. The present design addresses this situation by including a means of applying a threshold to an amplified version of the detection signal after the extraneous steady-state signal has been cancelled.
Another detection practice used by Fukuyama and Aromat adjusts the sensing area to exclude extraneous objects from a detection range. This is not adequate in the preferred application since extraneous objects (glass panes) are in intimate proximity to the object to be detected (finger).
Proximity detectors are used in industry to measure, for example, the web tension and accumulating roll diameter of winding fabric, proximity of microprobes from the surface of electronic parts, product width or position determination, and distance measuring on automatic vehicles. Typically ultrasonics are used in applications that resolve within a centimeter.
A reflective-type proximity detector offers the possibility of measuring displacement to a much finer resolution, albeit over a much shorter working distance, typically under 30 centimeters.
Reflecting-type infrared proximity detectors operate on principles similar to reflective-type proximity switches, having instead an analog signal output indicating the strength of the reflected signal, which increases as the object gets closer to the detector. One difficulty encountered by reflective-type proximity detectors is the tradeoff of sensitivity to incremental movements and saturation from total reflection.
This situation is similar to the case of the reflecting-type infrared switch where there is a small change in reflection (due to incremental movement) in the presence of a large background reflection (due to total reflection).
It is therefore a purpose of the design to create a reflective-type proximity switch that can detect the touch of a human finger, discriminated from stray radiation in a multitude of environments including the preferred application mentioned above. It is a further purpose of the design to produce an output which is relative and which increases as an object comes closer to the detector, removing the effect of total reflection to allow greater amplification of incremental movement.
In accordance with the present design, a proximity detector and switch is relatively simple in construction and circuitry, and highly accurate and sensitive in use. The principal circuitry can be used for detecting presence of an object to produce a binary output, i.e. as a switch, or a continuous output for determining the proximity of an object.
A principal object of the design is to provide a relatively simple and cost efficient system having a means of removing the effect of large background type or steady-state reflections to allow greater amplification of changes in reflection. A related object is to detect small incremental changes of reflection in the presence of large steady-state reception which may be from reflection or direct transmission or both.
Another object of the design is to produce an output that increases and decreases as an object incrementally moves respectively closer to and farther away from the detector.
Another object of the design is to provide a reflective-type proximity switch capable of binarily detecting finger proximity.
Another object of the design is to produce a binary output that indicates when an object to be detected is within a zone of proximity.
A further object of the design is to detect finger presence or proximity through one or more panes of glass that may include an air gap, by cancelling out the radiation reflected by the glass.
Another object of the design is to provide visual feedback to indicate the switch state of a touch sensitive switch.
Another object of the design is to provide a simple means to calibrate the switch during installation.
Another object of the design is to control electric devices with a photoelectric proximity switch, and particularly to allow a user outside a window to control displays of information or other visual material inside the window.
Another object of the design is to provide a system which will permit a computer or modem to control visual feedback to indicate when to touch the switch.
Another object of the design is to prevent unintended touches or objects moving past the switch from activating the output of the switch.
Another object of the design is to include several touch switches, serial communication with a computer, touch response delay, relays to control electric devices with the touch switches, visual feedback to indicate switch state, calibration state, and where and when to touch the switch, in a self contained system.
To achieve an output indicating proximity of an object, a photoelectric proximity detector according to the design includes a means for transmitting a modulated infrared beam, means for mechanically blocking stray radiation, means for optically selecting radiation in the spectral band of the transmitted beam, means for converting a received infrared modulated beam into an electric signal, means for electrically selecting signals at the modulation frequency, and means for electronically converting the modulation signal into a proximity level.
The system further includes means for electronically compensating for extraneous steady-state infrared modulated radiation picked up by the detector, and means for electronically amplifying the compensated proximity level.
To further achieve the goal of a photoelectric proximity switch or touch switch, the following elements are added to the photoelectric proximity detector described above: a means for electronically converting the compensated proximity level into a binary proximity state, and means for electronically delaying the binary proximity output by an adjustable delay.
The system thus produces a signal which can be used for touch detection, for communicating the binary proximity state to electric devices, computers and modems. These may be used to control displays of information, thus giving a user control of the displays by touch selection.
In one preferred embodiment of the design, an array of infrared light emitting diodes (IRLEDs) emit a beam of pulse modulated infrared radiation outwardly toward a sensing area. The IRLEDs are modulated together to produce a single-phase beam from the array. The beam is reflected off objects in the sensing area, and this reflected radiation is received and converted into an electric signal by an infrared phototransistor (IRPT).
The IRPT preferably includes an infrared filter integral in its construction, to optically block out-of-band radiation. An opaque tube is fitted around the IRPT to mechanically block off-axis stray radiation, effectively narrowing the sensing area.
The signal from the IRPT goes through a bandpass filter which electronically selects signals at the modulation frequency, and a half wave rectifying circuit converts this AC signal into a DC proximity level. An important feature of the design is that, after the described processing to produce a DC proximity level, a bias signal is subtracted from the proximity level to compensate for extraneous steady-state modulated radiation. This can be from glass surfaces, for example, in a through-the-window touch detector.
The compensated proximity level signal can be amplified and the result output as a proximity signal of the detector device. It can also be used to produce a binary output, to operate as a switch.
To implement the device as a photoelectric proximity switch or touch detector, the amplified compensated proximity level signal is converted into a binary output by comparison to a detection threshold. The comparison is made with hysteresis to prevent a jittery output when the two signals are near in value.
In a preferred implementation, the binary output of the comparison is delayed using a charging circuit to ignore quick unintended touches caused for example by a finger brushing over the photoelectric proximity switch.
In the specific embodiment of a touch detector, such as for enabling a user outside a store window to make touch selections to operate display equipment inside the store window, visual indications and visual feedback to the user are desirable. To this end, the proximity detector and switch of the design includes a visual means for indicating the location of the touch area, a further visual indication of the switch output, and a request for switch touch.
In a preferred embodiment of the design, the touch area or touch areas are indicated by illuminated light conducting acrylic target rings which circumscribe the IRLED arrays and the IRPT at each touch sensor, thereby circumscribing the touch area with a ring of light. This target ring preferably flashes to request a touch and to indicate that switch is detecting touch.
For calibration of the touch sensor or proximity device, i.e. to adjust the magnitude of the biasing signal which subtracts out steady-state extraneous signal detected by the detector, a bicolored LED is used to indicate the bias state, which is the sign of the relative magnitude of the compensation level as compared to the proximity level (without presence of a finger or other object to be detected) before the summation of the two levels is performed.
Upon installation of a touch detector, an installer adjusts the magnitude of the biasing signal to equal the magnitude of the uncompensated proximity level by observing the bicolored LED, which illuminates green when the bias signal is greater than the proximity level, red when the bias signal is less than the proximity level, and extinguishes when the bias signal is equal to the proximity level.
Once the bias signal is set, the sensitivity of the touch switch is adjusted by setting the gain of the amplifier, which amplifies the compensated proximity level signal, so as to produce a detection output when the object to be detected is in proximity to the touch sensor.
To carry out the purpose of communication with a user, such as in the environment of a store window, the proximity switch of the design includes a means for relaying the switch state to electrical devices including a computer connected to a display device, and optionally including a modem.
The display generated by the computer, in response to touch selections of the user, provides part of the visual feedback to the user. Thus, in addition to flashing illuminated target rings, a request for user selection can also be made by the display of information generated by a computer, such as a textual message.
Similarly, confirmation of user selection by the flashing of the target ring of the particular switch touched, while all remaining unselected switches revert to steady illumination of their target rings, can also be indicated by the computer display--for example, by graphically highlighting what has been selected.
In preferred embodiments of the design the binary switch state output of a touch switch can drive a relay that can turn on other electrical devices in response to the user's touch selection. Examples are video disk players, toy trucks, fans and light bulbs, as alternatives to strictly displaying information on a screen as described above.
A serial communication device can be included to enable a computer to interrogate the state of each touch sensitive switch, arm and reset a latch that stores the photoelectric proximity switch's touch state, and control the flashing of the target rings. Multiple switch panels, each containing a plurality of touch switches, can be in communication with one computer through a serial communication scheme wherein each unit is given a unique address and only responds to commands that contain its address.
Modem communication is achieved through use of a serial interface that connects to a telephone line. FIG. 1A is a front view of an optical assembly of a photoelectric proximity detector and switch in accordance with the design.
FIG. 1a and FIG. 1b show optical assembly components of the photoelectric proximity detector and switch 5 of the design. An array of IRLEDs 6 transmit modulated infrared light in beams represented by lines 7 and 8 through a plurality of glass panes 9 and 10 which include an air gap 11.
Such insulated double-pane glass is often used in store windows. As indicated by a line 12, some of the beam reflects back into an infrared phototransistor (IRPT) 13 by reflection off glass surfaces (which can include both inner and outer surfaces).
Some of the beam, as indicated at 14, is reflected back into the IRPT 13 by a finger 15 in proximity to the top or outer glass pane 10. The IRPT 13 is furnished with a black IR filter package (not shown). An opaque tube 16 preferably is included to sheath or shroud the IRPT 13, thus restricting the acceptance angle of the IRPT 13 and minimizing the detection of off-axis illumination such as represented by a ray 17 from the sun S.
Even if the sun's rays are filtered out of the system by the IR filter and by electrical components described below, the IR component of the sun's spectrum that passes through the IR filter can be strong enough to saturate the detector 13 and thus prevent good readings If the sun were in a position S' substantially aligned with the axis of the IRPT 13, allowing enough of the sun's rays 20 to pass axially through the opaque tube 16 and saturate the IRPT 13, the finger 15 would interrupt these rays 20, allowing the detection of the finger 15.
A light conductive target ring 18 in one preferred embodiment, which may be made of acrylic, is illuminated by an outer array of a plurality of visible LEDs 19, emitting constant or blinking light to indicate the status of the photoelectric proximity switch 5.
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