Large-screen Projection System Research Articles

Laser Illuminated Projectors and their Benefits for Immersive Environments

Laser-based illumination sources for projection systems are becoming a powerful alternative to conventional lamp-based light sources. The laser-based lights have a multitude of advantages over conventional lights, including brightness, longevity, scalability and others. The work described here looks at these advantages from a point of view of large-screen projection systems as used for immersive Virtual Reality systems. For these applications laser-based light sources are very useful, especially when using Infitec-base stereo glasses.

Viewing medium affects arm motor performance in 3D virtual environments

Background2D and 3D virtual reality platforms are used for designing individualized training environments for post-stroke rehabilitation. Virtual environments (VEs) are viewed using media like head mounted displays (HMDs) and large screen projection systems (SPS) which can influence the quality of perception of the environment. We estimated if there were differences in arm pointing kinematics when subjects with and without stroke viewed a 3D VE through two different media: HMD and SPS.MethodsTwo groups of subjects participated (healthy control, n = 10, aged 53.6 ± 17.2 yrs; stroke, n = 20, 66.2 ± 11.3 yrs). Arm motor impairment and spasticity were assessed in the stroke group which was divided into mild (n = 10) and moderate-to-severe (n = 10) sub-groups based on Fugl-Meyer Scores. Subjects pointed (8 times each) to 6 randomly presented targets located at two heights in the ipsilateral, middle and contralateral arm workspaces. Movements were repeated in the same VE viewed using HMD (Kaiser XL50) and SPS. Movement kinematics were recorded using an Optotrak system (Certus, 6 markers, 100 Hz). Upper limb motor performance (precision, velocity, trajectory straightness) and movement pattern (elbow, shoulder ranges and trunk displacement) outcomes were analyzed using repeated measures ANOVAs.ResultsFor all groups, there were no differences in endpoint trajectory straightness, shoulder flexion and shoulder horizontal adduction ranges and sagittal trunk displacement between the two media. All subjects, however, made larger errors in the vertical direction using HMD compared to SPS. Healthy subjects also made larger errors in the sagittal direction, slower movements overall and used less range of elbow extension for the lower central target using HMD compared to SPS. The mild and moderate-to-severe sub-groups made larger RMS errors with HMD. The only advantage of using the HMD was that movements were 22% faster in the moderate-to-severe stroke sub-group compared to the SPS.ConclusionsDespite the similarity in majority of the movement kinematics, differences in movement speed and larger errors were observed for movements using the HMD. Use of the SPS may be a more comfortable and effective option to view VEs for upper limb rehabilitation post-stroke. This has implications for the use of VR applications to enhance upper limb recovery.

Software tools to improve note-taking in the classroom

This paper describes the functionalities and some implementation details of software tools to assist and to improve the process of note taking by students during a traditional lecture. The software tools allow professors to interact effectively with the students during lectures and help students to take relevant notes. They are based on a previously described software, and use a network of pen-based computers as well as a large screen projection system.

Large-screen projection system with a laser and an electro-optical amplifier

Large-screen projection system with a laser and an electro-optical amplifier

Development of amorphous silicon liquid crystal light valve

Using the amorphous silicon (a-Si:H) film, which is cheap and has a small time lag, as the photoconductive layer of the liquid crystal light valve(LCLV) is an ideal selection. With the method of impedance matching used, we have designed and fabricated an a-Si:H LCLV and have obtained a clear image on a large screen projection system. The resolution of the valve was 20 lp/mm. The sensitometry measurement showed that the projection light level varies linearly with the writing light level when the latter is below 100 μW/cm2. The measurement of the transient response at the writing light level of 100 μW/cm2 indicated that the rise time and the decay time were 60 ms and 80 ms, respectively.

Electro-optical applications of liquid crystals

The unique properties of thermotropic liquid crystals have led to the development of many new electro-optical devices, particularly for display applications. Basic properties and surface alignments of liquid crystals are reviewed with regard to these applications. Electro-optical effects based on conductivity and field effect alignment are described for both nematic and cholesteric materials. Three applications of nematics are selected for more detailed discussion: a flat panel television display using dynamic scattering activated by a semiconductor matrix, a watch display using polarization modulation of twisted nematic cells on transparent segment electrodes, and a large screen projection system using tunable birefringence in a photoactivated light valve.

The Fischer large-screen projection system

The paper describes the Fischer system of large screen television projection which makes use of an “eidophor” liquid. Consideration is given to the brightness requirements, and the principles of the schlieren optical system are discussed together with the manner in which the Eidophor functions. The technical problems involved are dealt with and the results obtained with the third prototype examined.