GB2401198A

GB2401198A - A mirror position control system for a rear projection display.

Info

Publication number: GB2401198A
Application number: GB0309986A
Authority: GB
Inventors: Leslie John Yare
Original assignee: Densitron Technologies Ltd
Current assignee: Densitron Technologies Ltd
Priority date: 2003-04-30
Filing date: 2003-04-30
Publication date: 2004-11-03
Also published as: GB0309986D0

Abstract

A mirror position control system and method for a rear projection display is disclosed. The control system includes a controller, a plurality of actuators for changing the position of the mirror and position sensing means for sensing the position of the mirror, the controller being arranged to control selected ones of the actuators to move the mirror in dependence on a mirror position control request, wherein the controller is arranged to process signals from the position sensing means to determine acceptability of mirror position and orientation, the controller being arranged to restrict movement of at least selected ones of the actuators if it is determined that an unacceptable position or orientation is reached.

Description

24011 98 Rear Projection Display System

Field of the Invention

The present invention relates to rear projection display systems and in particular to rear projection display systems intended to be situated in inaccessible positions.

Background to the Invention

Large and open areas such as airports, railway stations and other public locations require large information displays for the public to view easily.

One of the various technologies used to produce high-resolution largescale images for this type of environment is rear projection.

In rear projection systems, mirrors are often used to achieve the desired enlargement and change the direction of a light beam from a light source. Typically, a light source will bounce from one mirror to another and so on until the light reaches the rear side of a display screen. All of these components are contained within a cabinet, therefore necessitating precise alignment of the light source, mirrors and screen to align the image on the screen. Traditionally however, these types of mirrors have been fixed, preventing a user from adjusting the image projected to a desired place on the rear projection screen. Typically, the image that is projected is of a single size, even though it may be desirous to enlarge or shrink the image size. Also, in very large applications where an image or images are projected onto a plurality of screens, a seam can appear where image boundaries meet, thereby producing a non-contiguous image.

One of the more difficult design problems in rear projection systems is the placement of mirrors to optimise limited cabinet space. Many different configurations have been suggested that reflect images in different ways inside cabinets, with the initial beam of light being bounced off of at least one mirror.

Traditionally in rear projection systems, mirrors used to reflect light with an image contained therein have been securably mounted within the rear projection cabinet. By rigidly securing the mirrors within the cabinet, a user is unable to position the image on the screen as desired through mirror manipulation. While this is perhaps a minor inconvenience in a home viewing environment, in applications where the cabinet cannot be accessed easily for maintenance and/or where multiple projectors can be linked to produce a contiguous image, the inability to shift image position upon the rear projection screen using mirror manipulation is a problem. Although mirrors can be installed in a cabinet using movable mounts, there still remains the problem that many cabinets are positioned in inaccessible places making access to and movement of the mirrors a major inconvenience.

lO A further problem often faced in rear projection display systems is in maintaining a predetermined temperature within the cabinet. The light source necessary to generate a sufficiently large and bright image generates large amounts of heat and must be cooled, particularly if operated in a hot environment. Whilst complex cooling systems can be added to rear-projection display systems, such cooling systems add significantly to the size, weight and cost of the overall system. In some systems, fans are used to draw air through the cabinet to provide cooling. However, in drawing air into the cabinet, dust particles and the like are also drawn in. These dust particles build up over time and can obscure the light path and/or damage the light source.

Summary of the Invention

According to a first aspect of the present invention, there is provided a mirror position control system for a rear projection display comprising a controller, a plurality of actuators for changing the position of the mirror and position sensing means for sensing the position of the mirror, the controller being arranged to control selected ones of the actuators to move the mirror in dependence on a mirror position control request, wherein the controller is arranged to process signals from the position sensing means to determine acceptability of mirror position and orientation, the controller being arranged to restrict movement of at least selected ones of the actuators if it is determined that an unacceptable position or orientation is reached.

The position sensing means may comprise a plurality of sensors, at least one sensor being arranged to sense the position of each actuator, the controller being arranged to process the output signal of each sensor to determine the acceptability of the mirror position and orientation.

The controller may be arranged to determine the flatness of an n point plane using the output signal of each sensor, n being the number of actuators, wherein the flatness of the n point plane in an unacceptable position exceeds a predetermined value. The flatness of the n point plane may be predetermined in dependence on mechanical properties and flexibility tolerances of the mirror. If an unacceptable position or orientation has been reached, upon a subsequent position control request, the controller may be arranged to predict the output signal of each sensor based on the subsequent position control request and determine the flatness of the n point plane using the predicted output signals, the controller being arranged to permit said position control request if the flatness is determined to be less than a predetermined value.

One embodiment of the present invention seeks to provide a system in which a fine granularity of adjustment of internal mirrors is possible once the system is in place and in use. This arrangement offers a fast and simple set up and easy future adjustment. Preferably, the system is operable remotely allowing adjustment of mirrors without actually having to physically access them.

According to a second aspect of the present invention, there is provided a mirror position control method for a rear projection display comprising a plurality of actuators for changing the position of the mirror and position sensing means for sensing the position of the mirror, the method including: accepting a mirror position control request; controlling selected ones of the actuators to move the mirror in dependence on the mirror position control request; processing signals from the position sensing means to determine acceptability of mirror position and orientation; and, restricting movement of at least selected ones of the actuators if it is determined that an unacceptable position or orientation is reached.

The position sensing means may comprise a plurality of sensors, at least one sensor being arranged to sense the position of each actuator, the method including: processing the output signal of each sensor to determine the acceptability of the mirror position and orientation.

The method may include determining the flatness of an n point plane using the output signal of each sensor, n being the number of actuators, wherein the flatness of the n point plane in an unacceptable position exceeds a predetermined value. The flatness of the n point plane may be predetermined in dependence on mechanical properties and flexibility tolerances of the mirror.

If an unacceptable position or orientation has been reached, upon accepting a subsequent position control request, the method may include: predicting the output signal of each sensor based on the subsequent position control request; determining the flatness of the n point plane using the predicted output signals; and, permitting said position control request if the flatness is determined to be less than a predetermined value.

According to another aspect of the present invention, there is provided an actuator for moving a mirror in a rear projection display, comprising a piston driven by a motor, piston position sensing means and limit sensing means, wherein the piston position sensing means is arranged to communicate a feedback signal to the limit sensing means, the limit sensing means being arranged to stop the motor once the piston position sensing means detects the piston has reached a predetermined point.

The position sensing means may comprise a slider potentiometer, the piston including a slot for accepting a lever from the slider potentiometer.

Upon stopping the motor, the limit sensing means may be arranged to permit operation of the motor in a reverse direction.

According to a further aspect of the present invention, there is provided a cooling system for a rear projection display comprising an air suction system arranged to draw air through an inlet into a cabinet of the display and a first exhaust for expelling air, the inlet and first exhaust each including a filter for filtering the air, wherein the air suction system is arranged to maintain air pressure within the cabinet that is greater than the air pressure outside the cabinet.

Another embodiment of the present invention seeks to provide a simple yet effective S cooling system in which the build up of dust particles and the like within the cabinet is substantially eliminated.

The design of the filtration system has lead to the maintenance of rear projection systems being much reduced for all areas, specifically the mirror chamber where it is desirable to keep the whole chamber as debris / moisture free and undisturbed as possible.

The cabinet may include a mirror chamber for housing mirrors and the screen of the display and a projector chamber for housing the projector, the mirror chamber being IS in communication with the projector chamber via a further exhaust, the further exhaust including a filter, the inlet being positioned to communicate air to the mirror chamber and the first exhaust being positioned to accept air from the projector chamber.

Brief Description of the Drawings

Examples of the present invention will now be described in detail, by way of example only, with reference to the accompanying drawings in which: Figure I is a schematic diagram of a rear projection display system according to an embodiment of the present invention; Figure 2 is a schematic diagram illustrating various aspects of the system of Figure 1 in more detail; Figures 3a and 3b are perspective views of an actuator according to an embodiment of the present invention; Figures 3c and 3d are cross sectional views of the actuator of Figures 3a and 3b; Figure 4 is a flow diagram of a control system for use in the system of Figure 1; Figure 5 illustrates a user interface for use in the system of Figure 1; Figure 6 is a schematic diagram of the rear projection display system of Figure I incorporating a filtration system according to another embodiment of the present Invention; and, Figure 7 is a schematic diagram of a data network including a number of rear projection display systems of Figure 1.

Detailed Description

Figure I is a schematic diagram of a rear projection display system according to an embodiment of the present invention.

A rear projection display system 10 includes a light source 20, a primary mirror 30, a secondary mirror 40 and a screen 50. The light source 20 directs an image light path (shown by dashed lines) onto the primary mirror 30 Initially. The primary mirror 30 bounces the image light path onto the secondary mirror 40 which then projects the final image through the screen 50, enlarged by many times, as is usual for a rear projection unit.

Figure 2 is a schematic diagram illustrating various aspects of the system of Figure 1 in more detail.

It is important the mirrors be in the correct position for the image to be displayed properly and clearly on the front screen. In the present embodiment, a system is provided that permits adjustment of the mirrors for a perfectly positioned final image.

To achieve this, four actuators (30a-d; 40a-d) are used with each mirror 30, 40. One actuator is positioned at each corner of each mirror. The actuators are preferably remotely controllable to move the mirrors to achieve necessary position adjustment of the mirrors 30, 40.

Preferably, a control system is used to control the actuators 30a-d, 40ad. Under the supervision of the control system, the actuators work together to move the mirrors slowly and carefully into position.

Preferably, the control system is designed so that it is impossible to move the mirror into a position that would over adjust it, causing damage or warping.

Figures 3a and 3b are perspective views of an actuator according to an embodiment of the present invention. Figures 3c and 3d are cross sectional views of the actuator of Figures 3a and 3b, Figure 3d being a cross section along the line x-x of Figure 3c.

S The actuator 100 includes a mechanical piston 110 connected to a 12v do motor 120.

The motor 120 can be driven in both directions from a dedicated motor controller 130.

A slot 140 in the piston 110 accepts a lever 150 from a slider potentiometer 160. The mirror 30, 40 is mounted in a protective frame 170 which is in turn attached to a mounting frame 180. The actuator is connected to the mounting frame 180 via a spacer 190 and connector l 9S.

The potentiometer 160 provides a feedback signal to the control system (not shown).

Additionally, the slider potentiometer 160 feeds limit-sensing circuitry in the motor controller 130 which is arranged to stop the motor 120 when it is detected that the IS piston 110 has reached a predetermined point designating the end of allowed travel.

Once the motor 120 has been halted by the limit sensing circuitry, the direction signal must be reversed. This then allows the motor 120 to be driven in the opposite direction.

Motion of the piston 110 moves the slider potentiometer 160, which consequently changes the feedback signal to the control system. The control system simultaneously measures the other 3 feedback signals from the other actuators of the mirror currently being adjusted. Using this information, the control system applies an algorithm for determining flatness of a 4 point plane. Limits of this flatness are pre-programmed based on known mechanical properties and flexibility tolerances of the mirrors.

Figure 4 is a flow diagram of a control system for use in the system of Figure 1.

In step 200, a value for the feedback signal from each actuator is obtained. For example, if the primary mirror 30 of Figure 2 was being controlled, the values obtained for actuators 30a, Job, 30c and 30d are A, B. C and D, respectively. Each value is within a predetermined range, for example between 0 (no extension of piston) and 256 (maximum extension of piston).

In step 210, it is determined if the side between actuator 30a and 30b has become twisted by determining if the difference between A and B is greater than a predetermined limit x. In step 22O, it is determined if the side between 30c and 30d has become twisted by determining if the difference between C and D is greater than the predetermined limit x. If neither of the sides has become twisted then the system proceeds to step 260 where the motor is enabled, otherwise the system proceeds to step 230 In step 230, it is determined if the side between actuator 30a and 30c has become twisted by determining if the difference between A and C is greater than the predetermined limit x. In step 220, it is determined if the side between 30b and 30d has become twisted by determining if the difference between B and D is greater than the predetermined limit x. If neither of the sides has become twisted then the system proceeds to step 260 to enable the motors, otherwise the system proceeds to step 250 I S where the motor is disabled.

In the preferred embodiment, the algorithm is biased against a single actuator moving out of alignment with the others. If two actuators along a shared side are kept substantially aligned but moved out of alignment with the other 2 then this is acceptable to the algorithm. In this manner, tilting about a horizontal/vertical axis centred on the centre of the mirror is possible but twisting is prohibited beyond predetermined tolerances. The connection of the actuators to the frame allows a limited amount of relative movement to allow the other actuators to remain in place while the mirror is tilted, although ball and socket joints could be provided if full free movement was desired.

If the control system calculates that the mirror has become twisted, the motor(s) currently being activated are disabled and an indicator on a user interface device is activated. Further motion of the actuators of the mirror is only permitted by the control system if the requested direction of that particular motor will reduce the effect of the twist. The control system determines this by determining the direction request, feeding an anticipated feedback value into the algorithm and testing the outcome. If motion is acceptable the motors are re-activated and the indicator on the user interface is deactivated.

Preferably, each actuator is arranged to provide linear movement of the respective mirror of approximately +/- 1 Omm from the central position.

Figure 5 illustrates a user interface for use in the system of Figure 1.

Actuator control is preferably provided via a user interface 300. Preferably, the user interface is provided via a microcontroller-based remote control unit. A mirror selector switch 310 allows selection between the primary mirror 30 and the secondary mirror 40. A visualization of each actuator position of the mirror selected by switch 310 is provided by a display 320-350. Actuator control is performed by using a designated switch to control a single actuator or by use of a joystick. Selection between the individual switches 370-400 and joystick 410 is made using switch 360.

Switch 370 controls actuator 30a or 40a, switch 380 controls actuator 30b or 40b, switch 390 controls actuator 30c or 40c and switch 400 controls actuator 30d or 40d.

Each switch 370-400 has three positions: momentary-off-momentary. The rest position of the switch is off. The switches are manually activated forwards drives the actuator forwards; backwards drives the actuator backwards. The actuators are driven 3 so long as the switches are depressed (unless the control system intervenes - if the 3 user tries to drive the mirrors beyond the microcontroller's limits, an override button is provided for this purpose) and will stop as soon as the switch is released. PWM is not used to drive the motors when the system is in its normal (within tolerance) state.

Once the system has reached its limits the recovery phase exhibits what may be I described as PWM as it enables-disables the drive as a result of projected calculation/ real calculation of position - resulting in a halfspeed recovery.

When one of the switches is operated and selector 360 has enabled individual switches, the microcontroller detects the particular switch being operated and determines the direction of motion desired based on the switch position. If the control system has not disabled the requested direction of motion for the actuator corresponding to that particular switch, the microcontroller transmits a signal to the actuator commanding it to move a predetermined increment in the requested direction.

If the selector switch activates the joystick 410, all 4 actuators are controlled to move in the requested direction whilst keeping the mirror in a flat plane. If one or more actuators reach its predetermined travel limit, the actuator(s) concerned will stop by virtue of their local electronic limit control mechanism. The control system will S continue to calculate relative positions as usual. If the restricted actuator causes a system imbalance, the control system responds in the usual manner. Movement of an actuator which has reached the end of travel may always be reversed (i.e. end of travel is a recoverable situation).

The user interface includes an alarm indicator 420 that is illuminated if the control system determines the mirror has become twisted and inhibits further motion of the actuator(s) in the current direction.

The user interface may be connected to the display system via an umbilical cable, a computer network (as will later be described) or via a wireless link such as IEEE 802.11, Bluetooth or the like.

Figure 5 is a schematic diagram of the rear projection display system of Figure 1 3 incorporating a filtration system according to another embodiment of the present invention.

The system includes a cabinet 500 which is divided into a mirror chamber 501, within I which is mounted the primary 520 and secondary 530 mirrors and a screen 540, and a projector chamber 502 within which is mounted a projector 510. An air suction system 503 is provided to draw air into the mirror chamber 501. The position of the mirrors 520, 530 may be controllable, as described with reference to Figures 1 to 4, alternatively the position of the mirrors may be fixed.

The cabinet 500 is substantially sealed to the exterior environment with the exception of an opening hole 550 in the mirror chamber 501 which is provided with a filter 560 and exhaust louvers 570 that are also provided with filters 580. An exhaust 590 is provided between the mirror chamber 501 and the projector chamber 502 and is also provided with a filter 595.

Air is sucked through filter 560 into the cabinet 500 by the air suction system 503.

This creates positive pressure within the cabinet 500, inhibiting the ingress of moisture, debris, dust and the like. The air from the mirror chamber 501 is expelled through exhaust 590 into the projector chamber 502. Preferably, the air suction system moves air through the cabinet at approximately 40M3/hour, thereby maintaining positive pressure in the mirror chamber at around 5- 10 Pascals (N/mm2).

The air then exits through the exhaust louvers 570 carrying with it hot air created by the projector 510.

Preferably, the filters are filter membranes of G2 or G3 type to EN778 filter material such as synthetic 100% polyester fibres. Most preferably, the filters prevent the passage of particles greater than 10- 100 microns.

Figure 6 is a schematic diagram of a data network including a number of rear projection display systems of Figure 1.

The rear projection display system discussed above with reference to any of the preceding Figures can be connected to a data network 600.

The control system of each rear projection display system 610-630 includes a network controller for communication over the data network 600. Preferably, the control system is accessible via the data network and is able to provide operational and maintenance data on its respective on the rear projection display system and accept control and commands.

The data network may, for example, be a TCP/IP data network, in which case each controller would have its own IP address.

Video information may be transmitted over the data network 600. However, for reliability and reduced chances of interruption it is likely that a direct feed via cable or via a wireless link such as a radio frequency link 640 may be preferred.

A remote terminal 650 may include a control and diagnostics application arranged to communicate with and interrogate a selected display system. Preferably, all control and diagnostic functions are integral to the display system and only require the use of a device server to networkenable the function.

For example, the control and diagnostics application may allow the remote terminal 650 to control power to the display system and/or to the lamp. Furthermore, a software version of the user interface of Figure 5 may be implemented to allow the application to control mirror position over the network 600.

Diagnosis and maintenance information is preferably available from the control system, in particular data may be provided to enable: temperature monitoring, fan monitoring, lamp monitoring (ON, OFF, lamp fail), time since last filter change, current lamp running hours and total unit running time.

Preferably, the application monitors the diagnosis and maintenance information from each display system and invokes an alarm (such as on screen or via a call to a mobile phone or pager) if predetermined conditions are detected. The application may also be arranged to initiate an automatic shutdown in the event of a predetermined situation (such as an excessive temperature being detected) occurring. Redundant and/or backup fans may also be provided for cooling the system - activation and deactivation of these fans could be performed by the control system of the display screen or by the application.

Various improvements to conventional rear projection displays have been described.

It will be apparent to the reader that these improvements may be applied individually or together. For example, the actuator control system for moving mirrors may be based on actuators other than those described. In addition, the air cooling system may be used in combination with the above mentioned mirror control or separately.

Furthermore, it will be apparent to the skilled reader that references to microcontrollers could be substituted by controllers implemented by other means such as by general circuitry, by ASICS, FPGAs or in software. Viceversa, references to software interfaces and the like can be readily substituted by hardware equivalents. l

Claims

Claims 1. A mirror position control system for a rear projection display

comprising a controller, a plurality of actuators for changing the position of the mirror and position sensing means for sensing the position of the mirror, the controller being arranged to control selected ones of the actuators to move the mirror in dependence on a mirror position control request, wherein the controller is arranged to process signals from the position sensing means to determine acceptability of mirror position and orientation, the controller being arranged to restrict movement of at least selected ones of the actuators if it is determined that an unacceptable position or orientation is reached.
2. A mirror position control system according to claim 1, wherein the position sensing means comprises a plurality of sensors, at least one sensor being arranged to sense the position of each actuator, the controller being arranged to process the output signal of each sensor to determine the acceptability of the mirror position and orientation.
3. A mirror position control system according to claim 2, the controller being arranged to determine the flatness of an n point plane using the output signal of each sensor, n being the number of actuators, wherein the flatness of the n point plane in an unacceptable position exceeds a predetermined value.
4. A mirror position control system according to claim 3, wherein the flatness of the n point plane is predetermined in dependence on mechanical properties and flexibility tolerances of the mirror.
5. A mirror position control system according to claim 3 or 4, wherein if an unacceptable position or orientation has been reached, upon a subsequent position control request, the controller is arranged to predict the output signal of each sensor based on the subsequent position control request and determine the flatness of the n point plane using the predicted output signals, the controller being arranged to permit said position control request if the flatness is determined to be less than a predetermined value.
6. A mirror position control method for a rear projection display comprising a plurality of actuators for changing the position of the mirror and position sensing means for sensing the position of the mirror, the method including: accepting a mirror position control request; controlling selected ones of the actuators to move the mirror in dependence on the mirror position control request; processing signals from the position sensing means to determine acceptability of mirror position and orientation; and, restricting movement of at least selected ones of the actuators if it is determined that an unacceptable position or orientation is reached.
7. A mirror position control method according to claim 6, wherein the position sensing means comprises a plurality of sensors, at least one sensor being arranged to sense the position of each actuator, the method including: processing the output signal of each sensor to determine the acceptability of the mirror position and orientation.
8. A mirror position control method according to claim 7, including: determining the flatness of an n point plane using the output signal of each sensor, n being the number of actuators, wherein the flatness of the n point plane in an unacceptable position exceeds a predetermined value.
9. A mirror position control method according to claim 8, wherein the flatness of the n point plane is predetermined in dependence on mechanical properties and flexibility tolerances of the mirror.
10. A mirror position control method according to claim 8 or 9, wherein If an unacceptable position or orientation has been reached, upon accepting a subsequent position control request, the method including: predicting the output signal of each sensor based on the subsequent position control request; determining the flatness of the n point plane using the predicted output signals; and, permitting said position control request if the flatness is determined to be less than a predetermined value.
11. An actuator for moving a mirror in a rear projection display, comprising a piston driven by a motor, piston position sensing means and hunt sensing means, wherein the piston position sensing means is arranged to communicate a feedback signal to the limit sensing means, the limit sensing means being arranged to stop the motor once the piston position sensing means detects the piston has reached a predetermined point.
12. An actuator according to claim 11, wherein position sensing means comprises a slider potentiometer, the piston including a slot for accepting a lever from the slider potentiometer.
13. An actuator according to claim 11 or 12, wherein upon stopping the motor, the limit sensing means is arranged to permit operation of the motor in a reverse direction.
14. A cooling system for a rear projection display comprising an air suction system arranged to draw air through an inlet into a cabinet of the display and a first exhaust for expelling air, the inlet and first exhaust each including a filter for filtering the air, wherein the air suction system is arranged to maintain air pressure within the cabinet that is greater than the air pressure outside the cabinet.
15. A cooling system according to claim 14, wherein the cabinet includes a mirror chamber for housing mirrors and the screen of the display and a projector chamber for housing the projector, the mirror chamber being in communication with the projector chamber via a further exhaust, the further exhaust including a filter, the inlet being positioned to communicate air to the mirror chamber and the first exhaust being positioned to accept air from the projector chamber.
16. A control system according to any one of claims 1 to 5, wherein the actuators each comprise an actuator as claims in any of claims 11 to 13.
17. A rear projection display including the on or more of the systems of claims 1 to 5 or 14 to 16. .
18. A rear projection display as herein described and with reference to the accompanying drawings.
l9. A mirror position control system as herein described and with reference to the accompanying drawings.
20. A cooling system as herein described and with reference to the accompanying drawings.

lO
21. An actuator as herein described and with reference to the accompanying drawings.
22. A computer program comprising computer program code means for performing all the steps of any of claims 6 to lO when said program is run on a 1 5 computer.
23. A computer program as claimed in claim 22 embodied on a computer readable medium.