U.S. patent application number 15/187691 was filed with the patent office on 2017-08-17 for optical micro-projection system and projection method.
This patent application is currently assigned to INTEL CORPORATION. The applicant listed for this patent is INTEL CORPORATION. Invention is credited to FAOUZI KHECHANA, LUCIO KILCHER.
Application Number | 20170237956 15/187691 |
Document ID | / |
Family ID | 42040412 |
Filed Date | 2017-08-17 |
United States Patent
Application |
20170237956 |
Kind Code |
A9 |
KILCHER; LUCIO ; et
al. |
August 17, 2017 |
OPTICAL MICRO-PROJECTION SYSTEM AND PROJECTION METHOD
Abstract
An optical micro-projection system comprising the following
components: at least one laser light source (200, 400, 402, 600);
at least one movable mirror (102, 103, 203) for deviating light
from said light source to allow generation of images on a
projection surface (104, 301, 303, 306, 603); a self mixing module
for measurement of the distance (604) between the projection source
and a projection surface, said self mixing module comprising:--at
least one photodiode (401, 601) for monitoring the light emission
power of the laser light source;--an optical power variation
counter for counting optical power variations (605); successive
displacements of said mirror allowing the self mixing module
providing successive projection distance measurements of a
plurality of points of said projection surface. A projection method
for optical micro-projection system and a distance measurement
method are also provided.
Inventors: |
KILCHER; LUCIO; (MONTREUX,
CH) ; KHECHANA; FAOUZI; (CRISSIER, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INTEL CORPORATION |
Santa Clara |
CA |
US |
|
|
Assignee: |
INTEL CORPORATION
Santa Clara
CA
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20170048505 A1 |
February 16, 2017 |
|
|
Family ID: |
42040412 |
Appl. No.: |
15/187691 |
Filed: |
June 20, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14681661 |
Apr 8, 2015 |
9374566 |
|
|
15187691 |
|
|
|
|
13358269 |
Jan 25, 2012 |
9004698 |
|
|
14681661 |
|
|
|
|
PCT/EP2009/059937 |
Jul 31, 2009 |
|
|
|
13358269 |
|
|
|
|
Current U.S.
Class: |
353/85 |
Current CPC
Class: |
H04N 9/3194 20130101;
H04N 9/3155 20130101; G06F 3/0304 20130101; G02B 26/0833 20130101;
G01S 17/42 20130101; H04N 9/3185 20130101; G01S 17/26 20200101;
G01S 7/4814 20130101; H04N 9/3188 20130101; H04N 9/3129 20130101;
G06F 3/017 20130101 |
International
Class: |
H04N 9/31 20060101
H04N009/31; G01S 17/10 20060101 G01S017/10; G02B 26/08 20060101
G02B026/08 |
Claims
1-17. (canceled)
18. A system comprising: a light source to emit light to a
projection surface; a photodiode to receive light reflected by the
projection surface; a distance evaluator to: determine a distance
between the light source and the projection surface based on the
received light reflected by the projection surface; and generate an
object distance map based on the distance, the object distance map
comprising an indication of whether one or more objects are
disposed between the light source and the projection surface; and a
light source adjuster to send a control signal to the light source
to cause the light source to adjust at least one property of the
emitted light to project an image onto the projection surface.
19. The system of claim 18, the control signal to include an
indication to adjust a power level of the emitted light.
20. The system of claim 19, the object distance map comprising an
indication that one or more objects are disposed between the light
source and the projection surface, the control signal to include an
indication to emit light at a low power setting.
21. The system of claim 20, the low power setting comprising
emitting light at a power level less than a maximum permitted
exposure setting for the light source.
22. The system of claim 19, the object distance map comprising an
indication that one or more objects are not disposed between the
light source and the projection surface, the control signal to
include an indication to emit light at a high power setting.
23. The system of claim 22, the high power setting comprising
emitting light at a power level greater than a maximum permitted
exposure setting for the light source.
24. The system of claim 18, the light source comprising a visible
light source and a non-visible light source, the photodiode to
receive non-visible light reflected by the projection surface and
the distance evaluator to determine the distance based on the
received non-visible light.
25. The system of claim 18, the object distance map comprising an
indication of whether a location of the one or more objects
relative to the projection surface, the system comprising an image
modulator to adjust at least one property of the image based on the
object distance map.
26. The system of claim 25, the object distance map comprising an
indication that one or more objects are disposed between the light
source and the projection surface, the image modulator to scale an
image based on the location of the one or more objects to project
the image onto a portion of the projection surface not obstructed
by the one or more objects.
27. A method comprising: projecting, via a light source, a light
beam at a projection surface; receiving light reflected by the
projection surface; determining a distance between the light source
and the projection surface based on the light reflected by the
projection surface; generating an object distance map based on the
distance, the object distance map comprising an indication of
whether one or more objects are disposed between the light source
and the projection surface; adjusting at least one property of the
light beam to project an image onto the projection surface.
28. The method of claim 27, comprising adjusting a power level of
the light beam.
29. The method of claim 28, the object distance map comprising an
indication that one or more objects are disposed between the light
source and the projection surface, the method comprising adjusting
the power level to correspond to a low power setting.
30. The method of claim 29, the low power setting comprising
emitting light at a power level less than a maximum permitted
exposure setting for the light source.
31. The method of claim 28, the object distance map comprising an
indication that one or more objects are not disposed between the
light source and the projection surface, the method comprising
adjusting the power level to correspond to a high power
setting.
32. The method of claim 31, the high power setting comprising
emitting light at a power level greater than a maximum permitted
exposure setting for the light source.
33. The method of claim 27, comprising: projecting, via a light
source, a non-visible light beam at a projection surface; receiving
non-visible light reflected by the projection surface; and
determining the distance between the light source and the
projection surface based on the non-visible light reflected by the
projection surface;
34. The method of claim 27, the object distance map comprising an
indication of whether a location of the one or more objects
relative to the projection surface, the method comprising adjusting
at least one property of the image based on the object distance
map.
35. The method of claim 34, the object distance map comprising an
indication that one or more objects are disposed between the light
source and the projection surface, the method comprising scaling an
image based on the location of the one or more objects to project
the image onto a portion of the projection surface not obstructed
by the one or more objects.
36. A method comprising: projecting, via a light source, a light
beam at a projection surface; receiving light reflected by the
projection surface; determining a distance between the light source
and the projection surface based on the light reflected by the
projection surface; generating an object distance map based on the
distance, the object distance map comprising an indication of
whether one or more objects are disposed between the light source
and the projection surface; adjusting at least one property of the
light beam to project an image onto the projection surface.
37. The method of claim 36, the at least one property a resolution,
scale, brightness, contract, or distortion.
38. The method of claim 36, comprising: determining a distance
between the light source and the projection surface at a plurality
of points based on the light reflected by the projection surface;
and determining a volume of the one or more objects based on the
distance at the plurality of points; and adjusting at least one
property of the light beam to project the image onto the projection
surface based on the object distance map and the volume.
39. The method of claim 38, wherein the image is a
three-dimensional image.
40. The method of claim 38, wherein the image corresponds to a
virtual scene.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of, claims the benefit of
and priority to, previously filed U.S. patent application Ser. No.
14/681,661 entitled "OPTICAL MICRO-PROJECTION SYSTEM AND PROJECTION
METHOD" filed Apr. 8, 2015, which is a continuation of U.S. patent
application Ser. No. 13/358,269 filed on Jan. 25, 2012 and
subsequently issued as U.S. Pat. No. 9,004,698, which is a
continuation of International Patent Application No.
PCT/EP2009/059937, filed Jul. 31, 2009. The subject matter of all
of the above is hereby incorporated by reference in their
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to an optical micro-projection
system comprising at least one laser light source and at least one
movable mirror, preferably of MEMS type. It also relates to a
projection method and a projection distance measurement method.
BACKGROUND OF THE INVENTION
[0003] The biological effects of electromagnetic radiation to human
beings can be divided into two categories, ionizing and
non-ionizing radiation. The first, ionizing radiation, is related
to cosmic and x-ray wavelengths and to nuclear radiation. The
second, non-ionizing radiation is related to ultraviolet, visible,
infrared, microwave, and radio wavelengths. Image and video
projection devices works within the visible spectrum of the light,
therefore, non-ionizing hazard has to be investigated and avoided
while running the device.
[0004] Biological effects of non-ionizing radiation are dependent
on the spectral region of the radiation (wavelength) and the
duration of the exposure to the radiation. Furthermore, the damage
to the eyes and skin is dependent on whether there was a single
exposure (acute) or daily exposure (chronic) to the radiation.
[0005] The eye, are generally considered to be the organ of the
body which is most susceptible to damage by radiation. The parts of
the eye that can be affected by radiation are the cornea, lens, eye
fluid, and retina. Different light radiation affects the individual
eye parts. The damage to any of the parts occurs when the light is
absorbed by the parts. The damage that takes place is dependent on
the ranges of the exposure levels and the time of exposure.
[0006] Visible wavelengths of radiated frequency range from 390 nm
to 750 nm, those wavelengths are generally refracted by the cornea
and absorbed by the retina.
[0007] The Maximum Permissible Exposure (MPE) of the eye to visible
radiations within 400-700 nm wavelengths is about 0.001 W/cm2 for
an exposure time of 10 seconds. Therefore a method to prevent
damage is needed to maintain an exposure lower than the authorized
MPE.
[0008] In addition, the eye is also sensitive to other wavelength
that can induce severe damage, in the ultraviolet and infrared and
therefore for device using such wavelength, a method for preventing
damage is also required.
[0009] In the past years, many different types of electronic
devices using laser units in order to perform one or more technical
functions have been developed. Micro-projections systems are among
these devices. With the growing demand for laser diode for various
applications such as telecom and laser pointer device, the eye
safety issue for human became an issue and was mainly handled by
different methods. The simplest method was to use stickers placed
at the tip of the laser pointer device and warning the user to
avoid any direct eye illumination with the laser. Another method
was to develop a specific driving electronics in order to avoid any
peak current in the laser diode if electrical failure occurs or to
completely switch off the current in the laser diode above a
certain current level.
[0010] More advanced technique where described in past for eye
laser safety, using CCD detector coupled with the laser source. The
CCD detector detects the motion of an object or a person in its
vision field and sends a signal to stop the laser in the case of a
movement.
[0011] Other technique use motion sensor, such as accelerometers
or/and gyroscope, coupled with the projection system and sense
motion of the projector itself, and then send a signal to the laser
source to either switch off or lower the intensity. Other
techniques also have been tested in the past using capacitive
sensor where one electrode is placed in the measurement tool and
the human body acts as a second electrode. The human presence is
then sensed by the created voltage shift between these two
electrodes.
[0012] A problem of these laser safety techniques, for the specific
laser projection application, is that none of these existing
techniques are completely efficient, as the existing solutions do
not prevent eye damage if the user switches on the projector while
he looks directly toward the light source and while not moving.
This specific aspect and possible risk damaging the eye, is
possibly one of the key stoppers for the use of such laser
projector by a large number of people and especially by children.
Moreover, most of these techniques are complex and expensive.
[0013] Another problem of the existing techniques to prevent eye
damage is that the use of a CCD detector or capacitive detection do
not allow having a directional sensing and is typically much larger
that the field of projection of moving object. The result is that a
moving object placed outside the field of projection, and then
fully safe in terms of eye safety, will be sensed by the CCD
detector and will either stop of lower the projection intensity of
the laser. For hand-held application of laser projector, this
working behaviour, even though allowing eye safety apparatus is
therefore not adapted to normal operation and use. Indeed the user
should be able to use the laser projector in a crowed place and
should be able to project while maintaining the projector in its
hand, and during any motion.
[0014] A further problem of the eye safety technique while using
laser source, is that the use of a CCD detector or an external
motion sensor further increase the complexity of the overall
laser-based projection system by adding a different technology to
the technology initially used for the projection purpose.
[0015] A known type micro-projection systems based on
Micro-Electro-Mechanical System (MEMS) is presented in FIG. 1A,
where two MEMS scanning mirrors 102 and 103 are reflecting a laser
light source 101 is order to project a two dimensional image on a
target screen 104. Other projection system, presented in FIG. 1B
and based on matrix of a large number of individual addressable
pixels 105, either based on either MEMS technology or Liquid
Crystal on Silicon could also use laser source to project
image.
[0016] A complete architecture for laser-based colour projection
using two One-Degree-Of-Freedom (1 DOF) MEMS scanning mirrors is
presented in FIG. 2. The laser beams 200 are combined using a beam
combiner 201 optic device and the resulting beam is entering a beam
splitter 202 and is deflected by the two MEMS scanning mirror 203
to project a two dimensional image. However, in existing projection
systems, there is no complete safety system that can avoid eye
damage when the eye is within the field of projection above the MPE
limit, as presented in FIG. 3.
[0017] Other electronic devices using self-mixing technique are
also known. For instance, WO2005/106634 discloses an apparatus for
handling sheet material or an optical input device, which employs a
relative movement sensor utilizing the so-called "self-mixing"
effect of a laser diode. A band pass filter is provided for
filtering the electric signal resulting from measurement of the
electric signal to reduce or substantially eliminate the effects of
both the low frequency carrier signal and the high frequency noise
present in such a signal. As a result, the precision of the laser
self-mixing translation measurements is significantly improved.
[0018] U.S. Pat. No. 6,233,045 relates to a self-mixing sensor
usable for remotely measuring speed, vibrations, range, and length
provided in a manner making the device practical for economic
implementation while retaining accuracy. In one embodiment, the
device is configured to avoid mode hopping, such as by providing
for relatively high loss for all modes other than the desired mode.
Preferably this is accomplished by utilizing laser types that have
a high degree of side mode suppression, such as DFB lasers or
through active or passive control of the amount of light permitted
to re-enter the laser.
[0019] However, these devices are of no use to provide
micro-projection system or methods.
[0020] WO2007/062154 relates to a method for compensating
non-uniformities of a projection surface in a front projection
display. The measured properties of the surface are used to provide
a screen compensation bitmap or a screen compensation convolution
table. To obtain the screen compensation map, the method involves
measurement of brightness for each pixel and storing the related
values in the map. The compensated image is obtained in modifying
the grayscale values of the pixels in the video image according to
corresponding values in the screen compensation map to produce a
compensated video image signal.
[0021] According to this method, the applied correction directly
depends on the projected image. Thus, if an image showing an
irregular surface such as a cushion or non ironed clothes or
sheets, etc, is displayed, the projection system will use the
method to compensate the image as if the irregularities where
caused by the projection surface. Moreover, the correction depends
on the image taken by an additional camera or device which is not
perfectly aligned with the projection system, which adds to the
cost and complexity, and creates parallax errors. This device is of
no use for eye-safety.
[0022] US2009/0147272 describes a proximity detection method for
controlling of an imaging device. A proximity detector is capable
of estimating the distance from an object to the projector. If an
object is detected within a minimum distance, the projector
operation may be altered, for example to cause the projector to
turn off or to reduce the intensity of the emitted light below a
selected range. In a first embodiment, the detection module uses
periphery detection to detect the presence of an object in front of
the projector. The proximity detector projects nearly collimated
beams of infrared light to create spots that are placed around a
display region projected by a projector. The reflected beams are
then detected by a linear array of sensors, which detects
reflection of the beams within a detection cone. In a second
embodiment, a detection module uses triangulation based distance
estimation to detect the presence of an object in front of the
projector. Such a system involves specific infrared emitters and
detectors in addition to the standard projection material. Distance
data involve only few points, therefore limiting accuracy and
potential other uses of the data. Again, the distance measuring
system is not aligned with the projection system, creating parallax
errors.
SUMMARY OF THE INVENTION
[0023] It is therefore an object of the present invention to
provide a method and a device providing protection for human and
animal bodies, and more particularly eye protection for humans
during use of a laser projection system.
[0024] It is another object of the invention to provide protection
means for a laser projection system that do not interfere with the
surrounding environment or do not provide false detection due to
objects that are not directly exposed to laser light.
[0025] It is a further objet of the invention to provide a
protection for laser projection system that is simple, reliable and
cost effective.
[0026] It is a further object of the invention to provide a
distance measurement method that is compatible for use with a micro
projection system.
[0027] According to the invention, these aims are achieved by means
of an optical micro-projection system comprising the following
components:
[0028] at least one light source;
[0029] at least one movable mirror for deviating light from said
light source to allow generation of images on a projection
surface;
[0030] at least one photodiode for receiving light reflected by
said projection surface;
[0031] a distance evaluation circuit for evaluating the distance
between the projection source and a projection surface based on
light deviated by said mirror and received by said photodiode.
[0032] Sharing a common deviation arrangement for illumination and
distance measurement is particularly advantageous. For instance,
distance measurement for each point or pixel is precisely based on
the same path followed by the lighting step, thus avoiding any
parallax imprecision.
[0033] The distance evaluation system uses similar technology
blocks, including a light source, as the ones used for the
projection system and therefore does not increase the complexity of
the whole system by adding a new different technology.
[0034] Distance measurement may be based on different technologies
such as time-of-flight evaluation or self-mixing for instance.
[0035] The light source is advantageously a laser light source. In
a variant, Digital Light Processing (DLP) technologies may be used
with such a system.
[0036] In a preferred embodiment, the distance evaluation circuit
is arranged for evaluating the brightness of light deviated by the
mirror and received by the photodiode in order to evaluate the
distance.
[0037] In an aspect of the invention, the circuit comprises a
self-mixing module and an optical power variation counter for
counting optical power variations (swings).
[0038] In another aspect of the invention, the same component is
used as said light source and as said photodiode.
[0039] In a further aspect of the invention, the photodiode is an
avalanche photodiode, said distance evaluation circuit being
arranged for evaluating the time-of-flight of the light between
emission by said light source and detection by said avalanche
photodiode.
[0040] In a further embodiment, the light source emits a modulated
light at a visible wavelength, said mirror deviating said visible
light so as to scan a visible image onto said projection surface,
said photodiode receiving said visible light reflected by said
projection surface.
[0041] In a still further embodiment, the system further comprises
at least one light source emitting a modulated light at a visible
wavelength, at least one additional light source emitting infrared
light at an infrared wavelength, and said mirror deviating said
visible light and said infrared light, so as to scan a visible
image onto said projection surface, said photodiode receiving said
infrared light reflected by said projection surface.
[0042] In a preferred variant, successive displacements of said
mirror allow distance measurements of a plurality of points of said
projection surface. Compiling the plurality of measured distances
then allows generating a projection distance map of the generated
points.
[0043] The resulting distance map is particularly useful on the one
end for enhanced safety, allowing detecting an object at any
position, and on the other end to enable further technical
features, such as brightness correction, image distortion
detection, volume calculation, profile detection, as further
discussed here after.
[0044] In still another variant, the laser light source is an image
projection light source usable alternatively in an image projection
mode and in a measuring mode during which the projection point does
not correspond to an image pixel.
[0045] The mirror is preferably a MEMS scanning micro-mirror.
[0046] In another aspect, the self-mixing module further comprises
a light amplitude measurement unit for measurement of reflective
light amplitude level on said projection surface. This enables the
system to compensate for brightness non-uniformity, by projecting
brighter image portions in specific zones and darker image portions
in other zones.
[0047] The optical micro-projection system is advantageously based
on Digital Light Processing (DLP) of Liquid Crystal Display (LCD)
or Liquid Crystal on Silicon (LCoS) matrix. The light source can
also be a Light Emitting Diode (LED) or Super luminescent Light
Emitting Diode (SLED).
[0048] In another aspect, the invention also provides a projection
method for optical micro-projection system comprising the steps
of:
[0049] a) providing at least one light source coupled to at least
one movable micro-mirror for deviating light from said light source
to allow generation of images on a projection surface;
[0050] b) receiving light reflected by said projection surface with
at least one photodiode;
[0051] c) with a distance evaluation circuit, evaluating the
distance between the projection source and a projection surface
based on the output of said photodiode based on light deviated by
said micro-mirror and received by said photodiode.
[0052] In a preferred embodiment, successive displacements of said
mirror allow distance measurements of a plurality of points of said
projection surface.
[0053] In a further embodiment, the method also comprise the
following steps:
[0054] a) for a first point (for instance an image pixel) in a
projection zone, generating a laser light signal for projection on
a projection surface via reflexion on said micro-mirror;
[0055] b) measuring the projection distance of this point from the
projection source;
[0056] c) displacing the micro mirror position to a new position
allowing projecting a further point;
[0057] d) projecting said further point with said laser light
source;
[0058] e) measuring the projection distance of this further point
from the projection system;
[0059] f) repeating steps "c" to "e" until the projection distances
for all points have been measured, and;
[0060] g) compiling the plurality of measured distances for
generating a projection distance map of the generated points.
[0061] Self-mixing technique is preferably used for distance
measurement. This technique is advantageously completed by optical
power variations counted with an optical power variation counter.
Other ways of measuring the distance are also possible, such as
time-of-flight evaluation for instance.
[0062] The light source arrangement differs in accordance with
several variants. In a first variant, the light source is also used
for image projection. In a second variant, the light source is used
alternatively in an image projection mode and in a measuring mode
during which the projection point does not correspond to an image
pixel. In a third variant, the light source is an infra-red laser
diode used specifically for distance measurement.
[0063] In a preferred embodiment, the output power from the laser
source is reduced if the measured distances indicate that for at
least one point, the distance value is below a given threshold
value.
[0064] Such a method enables for instance the detection of an
object placed in front of the micro projector emission light cone
and the subsequent reduction of the emitted light power in order to
enable safety operation modes. This is of particular interest, for
instance in uses related to prevention, such as eye protection and
other human and animal body parts safety apparatus. In such cases,
the reduced power is preferably set to values such that the Maximum
Permissible Exposure (MPE) of the eye is not reached.
[0065] The projection method for optical micro-projection system
may comprise the step of determining the position of an object
placed in the projection cone.
[0066] The projection method may comprise the step of determining
the profile of said object, and wherein the brightness of the image
projected onto said object is reduced.
[0067] The projection method, wherein signals representative of the
position of said object are used as data commands for a graphical
user interface.
[0068] The projection method for an optical micro-projection
system, wherein said image is projected onto a semi-transparent
projection surface, and wherein the position of an object behind
said projection surface is determined.
[0069] The projection method for optical micro-projection system,
wherein the position of several objects simultaneously present in
said projection cone is determined.
[0070] The projection distance map may also be used for different
purposes, in a plurality of applications, in particular, but not
exclusively, for micro projection systems.
[0071] In a first variant, the projection distance map enables
defining the profile of an object or person placed in front of the
expected projection surface. After such detection, the map can be
used to project around said profile.
[0072] In a second variant, the projection distance map is used in
order to determine volume dimensions. Considering the
high-resolution map obtainable with this method, volumes may be
measured in a very accurate, simple and reliable way. For
applications such as quality control, where large quantities of
components have to be measured accurately and quickly, the present
method is of particular interest. Volume measurements may also be
precisely performed with components or objects having complex
shapes or profiles.
[0073] In a third variant, the projection distance map is used in
order to detect any image distortion. In case of such detection, a
modulation of the mirror-scanning angle is calculated in order to
compensate the image distortion.
[0074] In still a further variant, the projection distance map is
used in order to adjust the image size and power brightness. This
may be done in order to optimize the projection functionality,
depending on user preference.
[0075] In a further aspect, the invention also provides a distance
measurement method, in particular for an optical micro-projection
system, comprising the steps of:
[0076] a) providing at least one laser light source coupled to a
movable micro-mirror and to a scanning control module for deviating
light from said light source for projection on a projection
surface;
[0077] b) receiving light reflected by said projection surface with
at least one photodiode;
[0078] c) with a measuring circuit using the same scanning control
module, evaluating the distance between the projection source and a
projection surface based on the output of said photodiode.
[0079] In a preferred embodiment, successive displacements of said
mirror allow distance measurements of a plurality of points of said
projection surface and compiling the plurality of measured
distances allow generating a projection distance map of the
generated points.
[0080] In such a distance measurement method, the projection
distance map is advantageously used in order to either determine
volume dimensions, or detect any image distortion or to adjust the
image size and power brightness.
[0081] Self-mixing technique or time-of-flight distance measurement
technique may be used for distance measurement.
BRIEF DESCRIPTION OF THE DRAWINGS
[0082] The foregoing and other purposes, features, aspects and
advantages of the invention will become apparent from the following
detailed description of embodiments, given by way of illustration
and not limitation with reference to the accompanying drawings, in
which:
[0083] FIGS. 1A and 1B describe known type laser projection systems
based respectively on MEMS scanning micro-mirror and matrix of
digital micro-mirror or Liquid Crystal on Silicon;
[0084] FIG. 2 describes a color projection system based on MEMS
scanning micro-mirror and multiple laser sources;
[0085] FIG. 3 describes an object in the field of projection of a
projector;
[0086] FIG. 4 describes the electrical equivalent circuit of a
laser diode;
[0087] FIG. 5A illustrates the working principle of the distance
measurement technique;
[0088] FIG. 5B is a schematic representation of the main components
of a micro-projection system according to the invention;
[0089] FIG. 5C is a schematic representation of the main components
of a variant of a micro-projection system according to the
invention;
[0090] FIG. 6 describes the system architecture for a projector
using MEMS scanning micro-mirror and laser light source;
[0091] FIG. 7 describes the system block diagram for the laser
projector;
[0092] FIG. 8 describes image distortion due to the projection on a
non-flat surface;
[0093] FIG. 9 describes the block diagram for the image distortion
compensation;
[0094] FIG. 10 describes the projection on a surface having various
depths;
[0095] FIG. 11 describes a projection method allowing projecting
images around a human body.
[0096] FIG. 12 describes a projection system that interacts with
the movement of the human body such as finger or hand.
DETAILED DESCRIPTION OF THE INVENTION
[0097] For clarity, as is generally the case in representation of
microsystems, the various figures are not drawn to scale.
[0098] Laser diodes are made of two discrete components, a laser
diode "LD" 400 and a photodiode "PD" 401, as presented in FIG. 4,
the first component is used to generate the laser light while the
second is used to monitor the light emission power of the laser
diode. For many applications the laser diode and the photodiode are
feedback looped to maintain the optical output power of the laser
diode constant, independently of the working temperature.
[0099] A laser diode remote sensing technique described by Thierry
Bosch in "An overview of self-mixing sensing applications" can be
used to measure displacement, vibration, velocity and distance by
using the Optical Feedback Interferometry (OFI) properties inside
the active cavity of the laser diode 600 (see FIG. 5).
[0100] FIG. 5A presents the Self-Mixing "SM" technique that
consists in injecting a triangular waveform modulated current 602
into the laser diode 600 to perform absolute distance 604
measurements of a stationary target 603. Indeed, by modulating the
injected current, the length of the equivalent laser diode cavity
is modified while the complex refractive index of the active cavity
is varying. Moreover, both the optical frequency and power are also
modulated. The emitted wavelength X then presents a triangular
shift AX, therefore the wave number (2.pi..lamda.) is shifted by
the amount (-2.pi..DELTA..lamda./.lamda.2). Optical power swings
occur while injecting the current with a triangular waveform
modulation. The absolute distance 604 measurement of a stationary
target can be performed by counting the N number of optical power
swings 605 during each modulation cycle, detected with the
integrated photodiode 601.
[0101] In alternative embodiments, absolute distance measurement
may be performed by evaluation of time of flight, based for example
on avalanche photodiode triggered by single photons and Time to
Digital Converter "TDC".
[0102] Micro-projection systems based on laser diode technology
classically use one or two micro mirrors to deflect the light beam
and generate the image pixel by pixel. The invention uses the "SM"
distance measuring technique coupled with one or two steering
mirrors to determine the distance of an object 302 placed in front
of the micro-projector light emission cone 300 as shown in FIG. 3.
The laser diode used to perform the "SM" distance measurement can
be the same one used as light source in the projection system. If
needed, an additional laser diode can be added to the projection
system, in order to perform the distance measurement without
disturbing the projection laser diodes.
[0103] FIGS. 5B and 5C show schematic representation of the main
components involved in the micro-projection system of the
invention. As shown in FIG. 5B, a laser diode 600 projects a laser
light on a projection surface 603 via a scanning mirror 613. At
least a portion of the light is reflected on the projection surface
and returns to a photodiode 601, adapted for monitoring the
reflected light. A circuit is provided for evaluation of the
distance between the projection system and the projection surface.
In the illustrated example, this circuit comprises a self-mixing
module 610 and an optical power variation counter 611, cooperating
with the laser diode 600 and the photodiode 601 and allowing
distance measurement using self-mixing technique. The self-mixing
module 610 and the optical power variation counter 611, using the
multiple distances resulting from the measurement steps, provide
projection distance maps 612, that may be used in further steps for
different applications as explained hereafter.
[0104] FIG. 5C shows a variant in which at least one Infra-Red IR
laser 614 is used. FIG. 6 shows an example of such variant where an
additional Infra-Red "IR" laser diode 402 is provided in order to
perform the distance measurement. As shown in FIG. 5C, a plurality
of laser diodes 600 is advantageously used, coupled or not to one
or more IR diodes 614.
[0105] The advantage of using an additional IR laser diode, instead
of one used as projector light source, is the non disturbance of
the projected image while the system perform a distance
measurement.
[0106] The device and method according to the invention enable
performing a distance measurement over the entire projection
surface 301. The distance measurement can be performed pixel by
pixel while the system is running. As a result of the "SM" distance
measurements, an object distance map (or projection distance map)
with the same resolution (or with a lower resolution) as the
projected image can be generated and used for a plurality of
applications. In a first example of application, the projection
distance map is used to detect an eventual object placed in front
of the micro-projector light emission cone 300. If the detected
object is placed too close to the projector emission window 300 the
light intensity is automatically reduced, in order to stay under
the MPE region, no matter which kind of object is detected.
[0107] The method and device of the invention allows completely
avoiding the human eye hazard by keeping the projected light
intensity lower than the eye damage soil at visible wavelengths. An
advantage of the invention consists on the fact that the laser
projection system is always safe for the human eye by instantly
reducing the output power.
[0108] Another aspect of the invention is the innovative way of
integrating the "SM" technique into the scanning laser based
projection system. Indeed the method and device according to the
invention allow minimizing the system complexity and avoid any
alignment issues, and insure that the measurement system does not
disturb the projection and degrade the image quality.
[0109] As shown in FIG. 2, the device of the invention uses one of
the laser diode 200 already used as light source for the projection
device in relation with the SM technique in the following specific
way: during the distance measurement time-frame, no pixel of the
image is projected with the laser diode used for the distance
measurement. In other words, if one laser diode "lambda" is used to
perform the distance measurement, during this time frame, either
all other laser diodes are switched OFF, or they are pulsed as
usually to project the image pixel, whereas the initial laser diode
"lambda" is actuated differently to perform the distance
measurement. For a three laser (RGB) projection for example, having
the green and blue color still pulsing image pixel as usual could
limit the image degradation. In fact, the normal pixel projection
way is to pulse the laser using a short pulse. However, in order to
use the SM technique, it is required to apply a triangular waveform
to the laser. It is therefore not possible to do the measurement
distance and the image projection at the same time without
degrading the projected image quality. The required time-frame for
doing the distance measurement, and therefore the number of image
pixel that will not be projected, depends on the normally used
pixel pulsation speed.
[0110] Similar assembly technique can be used to assemble the IR
laser source to the other optical components using passive
alignment technique. This technique has the further advantage to
perform the distance measurement at the same time as the other
lasers are used to project the image, while not disturbing the
image projection quality. Furthermore, the IR laser diode can be of
lower power compared to the ones used as light sources for the
projection system. The lower power can be explained by the higher
sensitivity of photodiodes at IR wavelength. The IR laser diode
power is always lower than the MPE value for his corresponding
wavelength, avoiding any possible eye injuries.
[0111] This fact then ensures eye safety from the IR source, always
staying under the MPE region and a lower power consumption of the
overall projection-distance projection system.
[0112] In addition, such optical architecture enables to detect an
object only within the cone of projection 300 of the device,
meaning only in the range that can be dangerous for the eye. The
invention provides directionality of the distance measurement only
in the needed scope range because the IR light follows exactly the
optical path of the visible light. It then prevents to
inadvertently reduce the power intensity if an object is placed
outside the projection cone, in a zone that should not be taken
into account. The complete expected functionalities of the device
are thus maintained.
[0113] FIG. 7 illustrates a further aspect of the invention. The
block diagram explains the relation between the distance
measurement and the regulated output laser power in order to stay
under the MPE region with objects at any distances from the
projector light source. In order to avoid any damage during the
starting up of the colour projection, in the case a person put the
projector in direct contact with the eye for example, a first
distance measurement is done with the low power IR laser, under the
MPE region. Then if the projection distance is sufficient to
maintain lower MPE limit, the visible laser sources are started. As
the measurement distance can be done at the same speed or faster
than the image pixel pulsation speed, any object of human entering
the projection cone can be detected fast enough to stay below the
MPE exposure limit. The system is also designed to shut down all
laser sources in case of failure of the distance measurement system
and/or a failure of one or two MEMS micro mirrors.
[0114] FIG. 8 illustrates another aspect of the invention related
to the use of such integrated measurement system in the projector
in order to compensate for the optical projection distortion that
arises when the projector projects non-perpendicularly to the
projection surface 303. Indeed, using the SM measurement technique,
not only the distance from the projector to the projection surface
can be measured but also the effective image size and shape on the
projection surface. This measurement also gives the information on
the parallelism of the image on the projected surface. Therefore,
as the width of each scanning line can be measured with the
described measurement system, the projection system is provided
with a loop control in order to modulate the scanning angle or to
alter the scanning pattern in order to compensate for the optical
distortion, as presented in the block diagram of FIG. 9. The
initial distorted image 304 can then be restored 305 according to
the proposed algorithm.
[0115] In a further aspect of the invention, the projection
distance map is used to measure the distance of any object placed
into the projection cone. As the number of measurement points can
be very high, a high resolution can be achieved. Because of the use
of laser light source, measurement in harsh environment and
especially outdoor and long-range measurement can be achieved.
[0116] Still a further aspect of the invention relates to the
optimization of use of such projection system. Indeed for the user
point of view, one of the main concerns is to maximize the
brightness of the projector, especially in bright environment,
while staying below the MPE region. To do this, the information
provided by the measurement distance is used to command the
scanning mirror angle and then the projection size is order to
maximize the projection brightness. Indeed, as presented in FIG.
10, in the case of a user projecting an image on a non-flat surface
306 that can even have various depth and cavities, the projector
brightness is automatically adapted to stay below the MPE region
based on the shortest distance between the projector and the
projection support. However in this specific case, the projector
capabilities and brightness functionality are greatly reduced due
to the presence of a small area on which maybe the user would not
want to project.
[0117] According to this further aspect of the invention, when the
measured distance between the projector and the projection support
show variations that can be linear or nearly-linear due to the
projection on a curved surface, or that can be abrupt, as seen in
FIG. 10, the projector either proposes to the user or performs
automatically modulation of projection scanning angle in order to
evaluate the optimum projection characteristics on a given surface.
In the case presented in FIG. 10, the optimum could be to reduce
the projection size to fit into 309 opening and then being able to
increase the output power from the projector to achieve a brighter
image, which was previously limited by the presence of the 306
surface. This optimum could be different depending on the
applications and can be either the brightness or the image
size.
[0118] In another aspect of the invention, the micro-projection
system detects the presence of an object or a human body within the
projection field and projects an image all around that object, as
presented in FIG. 11. This technical feature enables interactivity,
where a person 406 for example can be placed in a "virtual" scene
405 that is projected around him or her.
[0119] In a further application, the micro-projection system is
adapted to measure the distance between the projector and an object
at a high number of points, allowing calculating the volume of the
object. The system is then suited for three-dimensional
measurement.
[0120] In a further application of the invention, the system is
able to sense in two or even three dimensions the position of a fix
or moving object, as shown in FIG. 12, that could be for example a
human hand, finger or a stick or even the spot light coming from a
laser pointer. This information on position can be retrieved by the
processing system that commands the micro-projection system, and
used as an additional input channel, for example in order to adapt
the projected image according to the position of this object. The
motion of such object could also be sensed and the projected image
can be changed accordingly. With this system, it is possible to do
close to real time evaluation of position and speed of an object,
but it is also possible to sense the position and speed of multiple
objects simultaneously, for example in order to provide signals
representative of the 2D or 3D position of objects within the
projection cone, and to command the processing system
accordingly.
[0121] A typical application of such a system is a human-machine
interface to provide interactivity. The projected image 407 could
have some specific parts, 408 or 409 for example, that can be
dedicated for the object sensing and motion and where the image
brightness remains below the MPE region or lower, such as class 1
or class 2, in order to prevent any injury of a person moving in
this portion of the image. The rest of the projected image may be
brighter. The projected image may also comprise widgets, such as
buttons, scrolling elements, sizable windows, etc which can be
manipulated by a user for entering commands. Other body and hand
gestures may be executed in front of (or behind) the projection
surface in order to enter command. For example, a displacement of
the arm, or of the fingers, may be used for scrolling, panning, or
for moving an object in 3 dimensions. Moving arms apart or together
can be used for resizing objects.
[0122] The projected image may also be adapted to the position,
size and motion of the object, in order to project onto this
object, and/or around this object.
[0123] In one embodiment, the image is projected onto a
semi-transparent screen 411; in this case, an object behind the
projection surface, such as a human body 410, could also be
sensed.
[0124] In any cases, it is not mandatory that the object whose
position is sensed is in contact with the projected image screen:
an object can also be sensed if it is placed away from the
screen.
[0125] The system and method of the invention may use either laser
visible or infrared source, but all light sources having integrated
photodiode can be used, such as Superluminescent Light-Emitting
Diodes (SLED) or Light-Emitting Diode (LED) light sources.
[0126] Another aspect of the invention is that the system is
adapted to have a feedback on both the distance measurement from
the projector to the support and the amplitude of the reflected
light. This enables the system to determine information about the
projection support brightness. Indeed due to the light absorption
that depends on the support colour or roughness, the system is able
to control the laser power intensity in order to adapt it for the
support brightness. As an example, when projecting onto a surface
that have bright, grey and dark zones, the projector is able to
compensate for the different zones and then give to the user a
better visual comfort with uniform or adapted projection
brightness.
[0127] Those skilled in the art will also understand that the here
above described materials can be modified. Such alterations,
modifications and improvements are intended to be within the spirit
and scope of the invention. For instance, the projection system may
be a matrix-based projection system such as LCOS, DLP and LCD.
[0128] Accordingly, the foregoing description is by way of example
only and is not intended to be limiting.
* * * * *