**4. Typical optoelectronic scanners signals**

Different shapes of signals are generated during an optical scanning process, depending on the kind of light source and the sensor of the scanner. Some precision semiconductor optical sensors like CCD or PSD produce output currents related to the "centre of mass" of light incident on the surface of the device See [18]. All light registered by the CCD or PSD origi‐ nates an ideal signal shape as shown in figure 17(Image credit: Measurecentral.com).

A typical position measuring process includes an emitter source of light, as a laser diode or an incoherent light lamp and the position sensitive detector like CCD or PSD as a receiving device, which collects a portion of the back-reflected light from the target. The position of the spot on the PSD is related to the target position and the distance from the source, see[19].However, the real photon distribution on the sensor depends on the characteristic di‐ mensions related to the diffraction pattern of the light in the space. Common examples of signals generated by the light registered on a CCD camera appear in a study about superresolution by spectrally selective imaging, shown in figure 18 (Image credit: A.M. van Oijen and J.Köhler).

A Method and Electronic Device to Detect the Optoelectronic Scanning Signal Energy Centre http://dx.doi.org/10.5772/51993 405

**Figure 17.** Ideal photon distribution on CCD and PSD sensors.

more accurate and faster than CCD because the PSD is a continuous sensor, while CCD is a matrix of dots switched on and off and its resolution depends on how many dots are located

PSD has an infinite resolution because it is a continuous sensor, therefore the digital resolu‐ tion of a PSD depends not on the PSD itself. Alignment sensors using CCDs have to be pro‐ grammed to do multiple measurements at every step to improve accuracy and to lower noise because linear CCDs have a low resolution. To have the same accuracy of a PSD, CCD should perform no less than 32 measurements and hence calculate the average measure‐ ment. However, CCD is generally preferred to PSD because PSD needs an expensive circuit

Different shapes of signals are generated during an optical scanning process, depending on the kind of light source and the sensor of the scanner. Some precision semiconductor optical sensors like CCD or PSD produce output currents related to the "centre of mass" of light incident on the surface of the device See [18]. All light registered by the CCD or PSD origi‐

A typical position measuring process includes an emitter source of light, as a laser diode or an incoherent light lamp and the position sensitive detector like CCD or PSD as a receiving device, which collects a portion of the back-reflected light from the target. The position of the spot on the PSD is related to the target position and the distance from the source, see[19].However, the real photon distribution on the sensor depends on the characteristic di‐ mensions related to the diffraction pattern of the light in the space. Common examples of signals generated by the light registered on a CCD camera appear in a study about superresolution by spectrally selective imaging, shown in figure 18 (Image credit: A.M. van Oijen

nates an ideal signal shape as shown in figure 17(Image credit: Measurecentral.com).

on the sensor. Typically a linear CCD has 1024 or 2048 dots.

design including Analogue-to-Digital conversion [17].

**4. Typical optoelectronic scanners signals**

**Figure 16.** PSD Operating principle.

404 Optoelectronics - Advanced Materials and Devices

and J.Köhler).

**Figure 18.** Real photon distributions as a function of the detector for different diffraction patterns.

Based on A.M. van Oijen and J.Köhler study, we can observe that the spatial distribution function of light has an Airy-function-like shape, see [20]. It is well known that CCD, CMOS and SPD use the light quantity distribution of the entire beam spot entering the light receiv‐ ing element to determine the beam spot centre or centroid and identifies this as the target position. However, they are not the only sensors that generate a similar Gaussian-like shape, there are still a lot of sensors to be further investigated. For example, a simple photodiode can also originate a similar Gaussian-like shape, when it is used as a sensor on a scanner with a rotating mirror, [21]. Figure 19 below illustrates a hypothetical spot model, and at‐ tempts to explain how the signal is created by the photodiode on a scanner with a rotating mirror.

tre of the signal. In the following section, we propose a new method and its respective cir‐

A Method and Electronic Device to Detect the Optoelectronic Scanning Signal Energy Centre

http://dx.doi.org/10.5772/51993

407

**Figure 20.** Scanning sensor Gaussian like shape, measurements at different angular positions of the light source.

In the previous sections, we described different sensors and scanners that produce output currents related to the "the centre of mass" of the light incident in the surface of the device. In this section we will compare some techniques to find the energy centre of the signal and

Peak Signal Algorithms are simple statistic algorithms for non-normally distributed data series [23] to find the peak signal through threshold criteria statically calculated [23]. The al‐ gorithms which identify peaks in a given normally distributed time-series were selected to be applied in a power distribution data, whose peaks indicate high demands, and the high‐ est corresponds to the energy centre. Each different algorithm is based on specific formaliza‐ tion of the notion of a peak according to the characteristics of the optical signal. These algorithms are classified as simple since the signal does not require to be pre-processed to smooth it, neither to be fit to a known function. However, the used algorithm detects all peaks whether strong or not, and to reduce the effects of noise it is required that the signal-

**5. Signal processing methods to locate signal energy centre**

**5.1. Time-series simple statistics algorithms for peak detection**

to-noise ratio (SNR) should be over a certain threshold [23]:

eventually discuss their advantages.

cuit to find the centre of the signal by an optical scanner.

**Figure 19.** Principle of electrical signal formation during rotational scanning.

In this case, the signal created, as a similar Gaussian-like shape, goes up(Fig. 19, a) and falls down (Fig. 19, e), and a fluctuating activity takes place around its maximum area in figs. 19 (b-d). As we mentioned before, in a real practice the signal becomes noisy, see [22]. The ex‐ periment recently developed by Rivas M. and Flores W., with the scanner shown in Figure 6, for angular position measuring and using an incoherent light source and a simple photo‐ diode, validated the model shown in Figure 20. During experimentation, it has been ob‐ served that the optoelectronic scanning sensor (photodiode) output is a Gaussian-like shape signal with some noise and deformation. This is due to some internal and external error sources like the motor eccentricity at low speed scanning, noise and deformation that could interfere with the wavelength of the light sources. Other phenomena could also affect, though, such as reflection, diffraction, absorption and refraction, producing a as seen in Fig‐ ure 20.

As we can see, the photodiode signal originates a similar function to a CCD, consequently, it is possible to enhance the accuracy measurements in optical scanners with a rotating mirror, using a method for improving centroid accuracy by taking measurement in the energy cen‐ tre of the signal. In the following section, we propose a new method and its respective cir‐ cuit to find the centre of the signal by an optical scanner.

**Figure 20.** Scanning sensor Gaussian like shape, measurements at different angular positions of the light source.
