Illumination Control

Illumination needs to be adjusted depending on optical surface characteristics and the surface geometry of objects in order to obtain good quality images. The parameters to be adjusted include incident angle and the distribution and intensity of light sources. Figure 1.19 illustrates the typical configuration of such an illumination control system [Mitutoyo Co., 2001]. The system consists of a guardant ring fiber light source, a paraboloid mirror, a toroid mirror, and a positioning mechanism to adjust the distance between the object’s surface and the parabola mirror. The incident angle as shown in the figure is controlled by adjusting the distance, while the intensity of the light source at each region is controlled independently.

1.5.2.2 Sensing

Various types of opto-mechatronic systems are used to take measurements of various types of physical quantities such as displacement, geometry, force, pressure, target motion, etc. The commonly adopted feature of these systems is that they are composed of optical, mechanical moving, servoing, and electronic elements. The optical elements are usually the sensing part divided into optical fiber and nonfiber optical FIGURE 1.18 Enabling technologies for opto-mechatronic systems.

TABLE 1.1 Classification and Technology Transition State of Various Functionalities

optical motion capture, confocal sensor, AFM, camera, adaptive mirror

CMM: nano-probe system, fiber optic CMM

MO/OPME ME→O→O

Optical scanning Optical scanning device: galvanometer, resonant scanner, acoustics-optic scanner, polygon mirror, pan-tilt mechanism

Optical/visual scanning system: navigation/

surveillance robot, image recognition system, PCB inspection system, wafer inspection system

MO/OPME OE→ME→O

Optical actuator Hyper-sensitive light-driven device OPME OE→ME Visual inspection Devices: endoscope, ersascope

Inspection: PCB pattern/PCB solder joint inspection, weld seam pattern

OPME ME→OE→OE

Motion control Vision-guided machine/robot: weld seam tracker, mobile robot, navigation, visual serving end-effectors

Optical-based motion control: inspection head, auto focusing, optical-based dead reckoning, lithography state

OM OE→ME

Data storage Optical disk drive, DVD MO OE→O→ME→O

Data transmission Optical switch, optical filter, optical modulator, optical attenuator

MO O→ME→O

Data display Digital micromirror array (DMD) MO O→ME→O

Monitoring/control/

diagnosis

Machining process, smart structure, assembly process, semiconductor process,

monitoring/control, laser material process, welding process, textile fabric fabrication process, metal forming process

OM/MO O→ME→M

Three-dimensional shape reconstruction

X-ray tomography, x-ray radiography OPME E→O→ME→O

Optical property variation

Tunable laser, fiber loop polarization, frequency modulator, tunable wave length (Raman oscillator)

OPME E→M→O

Laser material processing

Laser cutting, laser drilling, laser welding, laser grooving, laser hardening, laser lithography, stereo lithography

OPME OE→O→M

Optical pattern recognition

Target recognition, target tracking, vision-based navigation

MO OE→ME→O

Optical/visual information feedback control

Pipe welding process, washing machine, arc welding process, laser surface hardening, SMD mounting, camera, smart car

OM/MO OE→ME→M

Illumination control Intelligent illumination system MO OE→ME→O

Remote monitoring/

Supervisory visual control, camera zoom control MO ME→ME→O

Note: OM, optical embedded mechatronics system; OPME, opto-mechatronically fused system; MO, mechatroni-cally embedded optical system; O, optical; OE, opto-electronic; ME, mechatronic; M, mechanical.

transducers. Recently these elements are accelerating the sensor fusion, in which other types of sensors are fused together to obtain necessary information.

When the three-dimensional objects to be measured are stationary, as shown in Figure 2.20(a), the three-dimensional scanning motion needs to be intentionally generated. Two methods are frequently used: (1) a sensor head (light source plus detector) is made to travel, or in some cases light sources or detectors can be moved while the object is standing stationary during measurement; or (2) the objects move sequentially relative to a stationary sensor head. If a moving object is being measured, the motion is not provided intentionally, but rather is the result of the movement of the mechanical part.

Optical-fiber-based sensing also utilizes this similar principle in which the motion of a sensing element (part) is provided either intentionally or unintentionally. The sensor shown in Figure 2.20(b) uses a modulated light amplitude due to the motion of external mechatronic parts. Microbending fiber sensors and the pressure sensors employing a deflective diaphragm are examples of an unintentionally driven sensing element being adopted. On the other hand, tactile sensing using servoing is an example of utilizing an intentionally driven sensing element, which can be found when grasping an object with a complicated surface where visual sensors cannot work well [Pugh, 1986].

Figure 1.20(c) shows a six-degree-of-freedom (6-D) sensory system employing the opto-mechatronic principle [Park and Cho, 1999]. The sensor is composed of a 6-D microactuator, a laser source, three PSD sensors, and a three-facet tiny crystal (or mirror) that transmits the light beam into three PSD sensors.

The sensing principle is that the microactuator is so controlled that the top of tiny mirror is always positioned within the center of the beam. In other words, the output of each PSD sensor is kept identical regardless of the object’s motion. A typical problem associated with optical sensing is focusing, which needs to be adjusted depending on the distance between the optical lens and the surface of the objects to be measured [Zhang and Cai, 1997].

1.5.2.3 Actuating

Two types of optical actuating principles are shown in Figure 1.21(a) and (b). Figure 1.21(a) adopts the photostrictive phenomenon, in which optical energy is converted to mechanical displacement of piezoelectric material. In Figure 1.21(b), optical energy is used as a heat generator, which causes a temperature-sensitive material (e.g., shape memory alloy) to move. These actuators can be used to accurately control the micromovement of mechanical elements.

Figure 1.21(c) depicts the configuration of an optical gripper using the bimorph optical piezoelectrical actuators [Fukuda et al., 1993]. The element of the optical piezoelectrical actuator (PLZT) is a ceramic polycrystalline material made of (Pb, La)(Zr, Ti)O3. When the ultraviolet (UV) beam irradiates from the surface of the PLZT, the PLZT is elongated due to the photostrictive phenomenon, which is the conversion of an electromotive force to strain by the piezoelectric effect. As shown in the figure, each actuator is composed of an optical-fiber carrying UV beam, a beam-directing mirror, and a piezoelectric element. When the UV beam is irradiated by the PLZT surface, the gripper can be open or closed due to the actuator of the PLZT. The displacement of the gripper at the tip is 100 µm.

FIGURE 1.19 Illumination control.