1. Field of the Invention
The present invention relates to an optical displacement meter, an optical displacement measuring method, an optical displacement measurement program, a computer-readable recording medium, and a device that records the program, for irradiating an object to be measured with light, receiving the light from the object to be measured with a light receiving device to obtaining an electric signal according to the receiving light, measuring a distance from a light projector to the object to be measured, a displacement of the object to be measured, and the like corresponding to the electrical signal.
2. Description of the Related Art
To measure the dimension, a movement amount, and the like of an object to be measured (work), an optical displacement meter to which triangulation measuring technique is applied is used. FIG. 93 is a block diagram showing the configuration of main components of a conventional optical displacement meter. In FIG. 93, a drive circuit 101 drives a laser diode (LD) 102 on the basis of a light output control signal Va. A laser beam emitted from the laser diode 102 is passed to a work WK via a projection lens 103. A diffusion reflection component and a specular reflection component in reflection light from the work WK are received by a light position detection device such as a PSD via the light reception lens 104. When the work WK is displaced in the direction shown by the arrow X, the position of a light spot moves on the light reception surface of a light position detection device 105. Two output signals according to the position of a light spot on the light reception surface are output from the light position detection device 105 and are subjected to current-voltage conversion in current-voltage converting circuits (I-V converting circuits) 106a and 106b. One of the output signals of the optical position detection device 105 has a current value proportional to the distance from an end of the light reception surface to the light spot, and the other output signal has a current value proportional to the distance from the other end of the light reception surface to the light spot. Therefore, on the basis of the current values of the two output signals, the displacement of the work WK can be detected.
In such an optical displacement meter, the intensity of reflection light varies according to the material of the work WK and the surface state of the work WK. Consequently, the light output of the laser diode 102 has to be adjusted so that the light reception amount of the light position detection device 105 becomes a certain level. FIG. 94 is a block diagram showing an example of a conventional control circuit for controlling the light reception amount in the light position detection device 105. The control circuit of FIG. 94 includes the current-voltage converting circuits 106a and 106b, an adder 112, a subtracter 113, an error integration circuit 114, a reference voltage generating circuit 115, and a light output adjustment circuit 111. The current-voltage converting circuits 106a and 106b convert the current signal of the light position detection device 105 to a voltage signal. The adder 112 adds voltage signals on the far side and the near side, and outputs the light reception amount of the light position detection device 105 as a light reception amount voltage VL. The reference voltage generating circuit 115 generates a predetermined reference voltage Vr. The subtracter 113 outputs the difference between the light reception amount voltage VL obtained by the adder 112 and the reference voltage Vr generated by the reference voltage generating circuit 115. The error integration circuit 114 integrates error signals VE output from the subtracter 113, and provides the integrated error signals as a control voltage VC to the light output adjustment circuit 111. The voltage of the light output adjustment circuit 111 is controlled so that the light reception amount voltage VL output from the adder 112 becomes equal to the reference voltage Vr generated by the reference voltage generating circuit 115. Therefore, by controlling the voltage of the light output control signal Va provided from the light output adjustment circuit 111 to the drive circuit 101 in FIG. 93, the light reception amount in the light position detection device 105 can be controlled to a predetermined level.
In such an optical displacement meter, the reception light amount largely fluctuates and corresponds to the reflectance of light of a work according to the color, roughness, angle, and the like of the surface of a work. When the reception light signal is too small, or too large due to saturation or the like, the measurement accuracy deteriorates. Consequently, a technique of performing a feedback control that adjusts the light emission amount of a light emission device and the amplification factor (gain) of an amplifier so that the peak value of a light reception amount (image signal level) becomes a target value is developed (refer to, for example, Japanese Unexamined Patent Application Publication No. 2006-010361). An optical displacement meter of the technique has, as shown in FIG. 95, a light emitting device 102B for irradiating the work WK with light, an image sensor 105B for receiving light from the work WK and generating an image signal, a signal processing circuit including an amplifier 146B for amplifying the image signal from the image sensor 105B, and a controller 144B that executes feedback control of at least one of operation amounts including a light emission amount of the light emitting device 102B and the amplification factor of the amplifier 146B on the basis of the image signal from the signal processing circuit. The variable range of at least one of the operation amounts in the feedback control can be changed. The controller 144B sets a proper variable range of the operation amount on the basis of data of the operation amount in a predetermined period in a variable range setting mode. As a result, as shown in FIG. 96, while keeping the advantage of performing the feedback control of the light emission amount of the light emitting device 102B and the amplification factor of the amplifier 146B, the technique realizes higher speed of measurement.
On the other hand, an apparatus for measuring the shape (profile) of a work using the principle of light sectioning is developed. The light sectioning is obtained by two-dimensionally expanding the principle of triangulation as shown in FIGS. 97A and 97B. Specifically, as shown in FIG. 97A, a laser beam LB emitted from a sensor head SH to the work WK is set in a band shape, and the triangulation is increased in the width direction (X direction). As a result, the triangulation measuring technique is enlarged in the width direction as shown in FIG. 97B. Consequently, line-shaped (linear) light receiving devices are used in the triangulation measuring technique. On the other hand, light receiving devices JS arranged two-dimensionally are used in the light sectioning method.
By using an optical displacement meter for measuring a profile by using the principle of light sectioning, a stereoscopic shape of a work is measured. In the case of measuring a stereoscopic shape, there is a case such that intensity of reception light largely fluctuates according to the surface state and angle of a work. Conventionally, as the light receiving device, a CCD or CMOS sensor whose sensitivity characteristic (light receiving characteristic) is linear is used. Consequently, when the light amount changes considerably in a work, multiple exposure process is performed. In the process, while changing the amount of projected light and shutter time on the reception light side, imaging is performed on the work a plurality of times. From a plurality of reception light images obtained, ranges in which the light amount is proper are extracted. By combining the extracted images, a single image is obtained.
In the multiple exposure, however, the imaging process is performed a plurality of times. There is a problem such that the time required for obtaining one profile is long. For example, a reception light image requiring 15 to 16 ms per exposure is captured five to ten times successively, so that it takes about 0.5 to 1 second. Consequently, the technique is not suitable for an application requiring immediacy such as an inline process. When a work is position-deviated during image capturing a plurality of times, an error occurs at the time of composition of the multiple exposures. In such a case, an error can be compensated via software. In this case, the process amount further increases.