CA2227710A1 - Distance-based control of lighting parameters - Google Patents

Description

. CA 02227710 1998-01-21 l'his invention is a system for automatically controlling the beam width (iris), beam focus, and other parameters of robotic lamps in dependence on the distance from t:he lamp to the surface onto which the light beam from the lamp is being projected (the "projection surface").

F'obotic lamps are used primarily in the entertainment indust:ry but have additional applications in areas such as promot:ion/advertising, architectural lighting, and so-called "immersive reality" among others. Robotic or "intelligent"
lamps can be remotely controlled by an industry standard protocol called "DMX-512". This is a high speed serial data protocol which allows remote computer control of many different features of the lamp fixtures such as the pan and tilt angle at which the beam of light is projected, beam intensity, colour selection, beam width (iris), focus, and light pattern ("gobo" selection) among others.

A problem for these computer controlled lamps is that, as the beam of light is moved via its pan/tilt controls, the width, focus and intensity of the beam change depending on how far away the lamp is from the wall, floor or other surface onto which the beam is being projected. Unless an adjustment is made, the width of the beam will be twice as wide when the projection surface is at twice the distance from the light. To make the beam width be the same, the lamp's iris or focal zoom control must be adjusted.

',imilarly, knowledge of the distance between the lamp and the projection surface would allow the beam of light to be kept properly focused continuously despite variations in this cListance caused by changing pan/tilt angles of the lamp (or, for that matter, moving projection surfaces such as mobile scenery) in real-time during a show.

According to the invention there is provided a method of measuring in real-time the distance between a robotic lamp and a moving projection surface at any instant and modulating at least one control parameter of the lamp in depenclence on said distance.

E~mbodiments of the invention will now be described with reference to the drawings in which:

E~'igures lA and lB depict the problem of maintaining constant beam width for a moving projection surface;
E~'igure 2 depicts one embodiment of the invention utilizing measurement phase difference of transmitted and reflec:ted light; and E~'igure 3 depicts another embodiment of the invention utilizing measurement of time delay between emitted and detect:ed pulses.

C)ne problem is easily understood from Figures lA and lB. E~igure lA shows a focused light source 12 projected on a projection surface 14 which is located a distance R from the light source. The image on the projection surface 14 covers an area of diameter D. Figure lB, on the other hand, shows the projection surface 14 having moved to a distance 2R from the light source 12. The diameter of the image has correspondingly grown to 2D although it would be desirable for it: to remain at the original size.

The problem may be solved, for example, by the system of Fiqure 2. At appropriate modulation frequencies, the phase difference will change linearly and uniquely with the distance between the light emitter and the projection surface. It should be noted that, depending on design/cost trade-offs, the functionality of the system blocks described below could be implemented in either the analog or the digital domain (or a mixture).

~ digital control electronics (DCE) module 16 manages the whole distance calculation process for the distance between lamp 12 mounted on pannable/tiltable platform 10 and a projection surface 14. It is controlled via input from a DMX-512 receiver 18 which connects both the light control electronics 20 and the DCE 16 to the outside world, allowing remote control of both the lamp's parameters and whether the DCE 16 generates any continuous feedback signals for the lamp. In some cases it will be desirable to switch between continuously modifying lamp parameters in response to distance or disabling continuous control and having direct external control over these parameters.

I'he DCE 16 controls pulse train generator 22 to cause it to produce pulses and to control the frequency/phase of the produced pulses. These pulses are then modulated by modulator 24 to add greater noise immunity and are converted into light and transmitted from an infrared (IR) laser transmitter 26 collinear with the visible focused light beam 28 prc,duced by the lamp 12. The laser beam 30, specularly reflects from the projection surface 14 and a certain fraction of this reflected light passes through IR bandpass filter 32 and into the lensed IR photodetector 34. The bandpass filter helps improve noise immunity by only allowing light close in frequency to the frequency used by the laser to pass through to the IR photodetector where it is converted from light into an electronic signal. This signal is routed through an amplifier 36 and then a demodulator 38 where the original pulse train is recovered.
The signal is then fed to a phase comparator 40 where it is compared with the signal being transmitted. The phase difference between these two signals will be linearly related to the distance between the light and the projection surface. This phase difference is read by the DCE which uses it to calculate the distance and generate feedback signals which are sent through the feedback encoder 42 to the light control electronics 20 to modify lamp parameters such as iris, focus, or intensity in real-time.

In the above embodiment, a laser is used by way of example. A laser light source has certain advantages with respect to noise rejection since its energy is concentrated in a very narrow frequency range thus engendering a high signal to noise ratio when appropriate filtering is used.
However, it should be realized that any light capable of being properly modulated and detected may be used. In particular, it is possible that it might be efficacious to modulate the light of the robotic lamp itself if it is of an appropriate type and intensity.

~ .dditionally, many robotic lamp designs depend on movinc mirrors to change the pan and tilt angles at which the light beam is projected. In these systems, the light bulb and its lens assembly are stationary and project the light beam onto a mirror mounted on a platform having two orthogonal axes (pan and tilt) of rotation controlled by motors. Redirection of the light beam is achieved by moving the mirror using the pan/tilt axis motors to be at a different angle from the incident light beam.

The embodiment of Figure 2 is equally applicable to this situation; the laser transmitter could be stationary and the IR laser light could be projected onto the mirror along with the visible light beam from the lamp itself. The only modification necessary would be to perform the distance measurement in such a way that there was no danger of measuring the distance between the laser and the mirror rather- than the laser and the projection surface.
Alternatively, the laser transmitter and photodetector are both small and light enough that they could be mounted on the mirror itself if this proved more practicable.

A second embodiment is shown in Figure 3. Here a narrow beam of high frequency ultrasonic sound pulses is used and the distance measurement for the distance between lamp 12 on platform lO and projection surface 14 is performed by measuring the time delay between when the pulses are emitted and when they are detected. This delay is linearly related to the distance travelled by the sound pulse.

A DSP (digital signal processor) 50 generates an ultra~onic pulse digitally and converts it to analog form by sending it to a digital to analog (D/A) converter 52. This analog pulse is then amplified by the amplifier 54 and converted into ultrasonic sound and transmitted using a narrow beam ultrasonic transmitter 56. The ultrasonic sound reflects off of the projection surface 14 and is detected by a narrow beam ultrasonic receiver 58. This converts the pulse back into electronic form. It is then filtered and amplified by the filter/amplifier 60 and converted from analog form to digital form via an analog to digital (A/D) convertor 62. This digital signal is then analyzed by the DSP 50 which measures the time delay between when the pulse was sent and when it arrived and calculates the distance based on this time delay value. The DSP 50 then generates appropriate feedback signals (if any are required) and sends them through the feedback encoder 64 to the light control electronics 20. The functioning of the DSP 50 is controlled remotely by DMX signals decoded by the DMX-512 receiver 18.
Both the DSP's functionality and the lamp's parameter can be directly controlled via DMX.

l'he comments about mirrored lamps made with regard to the laser system described above also apply here. There is no reason why the ultrasonic transmitter and receiver could not be statically mounted and send/receive signals by bouncing them off of a moving mirror or, alternatively, why one could not mount a lightweight ultrasonic transmitter/receiver on the same pan/tilt platform as the mirror itself.

Claims