Qian Zhou

A location system based on two-dimensional position sensitive detector used in interactive projection systems

The interactive projection systems have been widely used in peoples life. Currently the major type is based on interactive whiteboard (IWB). In recent years, a new type based on CCD/CMOS sensor is greatly developed. Compared to IWB, CCD/CMOS implements non-contact sensing, which can use any surface as the projection screen. This makes them more flexible in many applications. However, the main defect is that the location accuracy and tracing speed are limited by the resolution and frame rate of the CCD/CMOS. In this paper, we introduced our recent progress on constructing a new type of non-contact interactive projection system by using a two-dimensional position sensitive detector (PSD). The PSD is an analog optoelectronic position sensor utilizing photodiode surface resistance, which provides continuous position measuring and features high position resolution (better than 1.5μm) and high speed response (less than 1μs). By using the PSD, both high positioning resolution and high tracing speed can be easily achieved. A specially designed pen equipped with infrared LEDs is used as a cooperative target. A high precision signal processing system is designed and optimized. The nonlinearity of the PSD as well as the aberration of the camera lens is carefully measured and calibrated. Several anti-interference methods and algorithms are studied. Experimental results show that the positioning error is about 2mm over a 1200mm×1000mm projection screen, and the sampling rate is at least 100Hz.

Indirect measurement of the infrared pen point used in a short throw interactive projection system

Short throw interactive projection systems are widely used in education, training, commerce, and entertainment in recent years. Different interactive techniques have been developed. And among them, the infrared location technique is one of the attracting methods, because of the advantages such as independent of whiteboard and low cost, and so on. However, the main defect is that the infrared pen point is easy to be blocked by users hand. In this paper, we introduced our recent progress on indirect measurement of the pen point used in a short throw interactive projection system. Two infrared LEDs are fixed along the pens body near the tail end. By separately measuring the position of the two LEDs, the location of the front end pen point can be calculated. Such placement can effectively avoid the LEDs from being blocked by users hand. The mathematical model of this measurement scheme is given separately in the situations of infinite focal length and short focal length of the camera. Errors are analyzed by both analytical and numerical method. We used our position sensitive detector (PSD) based location system to test the effect of this method.

A two-dimensional location method based on digital micromirror device used in interactive projection systems

Interactive projection systems based on CCD/CMOS have been greatly developed in recent years. They can locate and trace the movement of a pen equipped with an infrared LED, and displays the users handwriting or react to the users operation in real time. However, a major shortcoming is that the location device and the projector are independent with each other, including both the optical system and the control system. This requires construction of two optical systems, calibration of the differences between the projector view and the camera view, and also synchronization between two control systems, etc. In this paper, we introduced a two-dimensional location method based on digital micro-mirror device (DMD). The DMD is used as the display device and the position detector in turn. By serially flipping the micro-mirrors on the DMD according to a specially designed scheme and monitoring the reflected light energy, the image spot of the infrared LED can be quickly located. By using this method, the same optical system as well as the DMD can be multiplexed for projection and location, which will reduce the complexity and cost of the whole system. Furthermore, this method can also achieve high positioning accuracy and sampling rates. The results of location experiments are given.

Indirect real-time measurement of the penpoint in an interactive projector-camera system

Real-time interactive on documents can enhance effectiveness of learning in modern education. A pen capable of locating on a screen is one significant choice. Some products have been developed and the nib of pen is used as the emitter. However, the pen might fail to be located while our body or hand would block the light wherever the photo detector is. In this paper, we have proposed a scheme to solve the problem. It will detect the nib of pen indirectly. Meanwhile, for the realization of real time, we choose PSD(position sensitive detector) as the detector to track the light of the LEDs. And by using the method of coding, multiple light points detected by one PSD could be achieved.