JPH0141202B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a measurement head for measuring the shape and position of a workpiece in a welding robot. When measuring the position of a bright spot, that is, a bright spot that occurs at the projection point, with a receiver, the welding arc This is intended to improve measurement accuracy by reducing interference caused by optical noise.

In order to determine the shape of an object with conventional robot measurement, a method has been used in which the object is imaged with an image camera and the image is processed with a computer to extract the required features. It is troublesome to remove interference from noise light emitted by the welding arc, and it is difficult to determine the irregularities of the object to be measured.
A method using a magnetic sensor has also been used, but it has drawbacks such as the inability to accurately measure the shape of the object to be measured.

The present invention includes a light emitter that emits a modulated narrow light beam as a signal light, and a light receiver that captures a bright spot created by the signal light on an object to be measured. The position of the measurement point is determined from the line of sight of the light beam and the line of sight of the receiver.The focus adjustment of the projector is necessary to clarify the bright spot that the light beam forms on the object to be measured, and the image of the bright spot is transferred to the receiver. The measurement accuracy is improved by automatically adjusting the focus of the light receiver so that the light is clearly focused on the light receiving sensor.

FIG. 1 is a diagram showing the measurement principle of the present invention. In the figure, B is the measurement head body, and two points O _L and O _R , which are separated by a certain distance d on the central axis ξ, are the emitter L and the light receiver, respectively. A modulated light beam L _is projected from the projector L onto the surface J of the object to be measured, creating a bright spot A on J, and the bright spot A is captured by the receiver R. , forms a bright spot image on the light receiving sensor of the light receiver R, and produces an electrical output from the light receiving sensor. The light receiver consists of a light-concentrating lens L and a light-receiving element s.If we call the direction of the straight line connecting the light-receiving element and the center O _R of the lens the line of sight _Lr , we can know the direction of the light beam and the line of sight. For example, the position of bright spot A is calculated by trigonometry. With O _L as the origin, take the coordinate axes ξ, η, ζ fixed to the measurement head as shown. It is assumed that the measurement head B is supported by the arm of the robot and can assume a desired position and posture. In addition, the light beam L _s and the line of sight L _r are O _L and O _R respectively in the same plane (ξζ plane).
The direction can be changed according to a periodic function of time with the center at θ _L (t) for the light beam and θ _R (t) for the line of sight.
shall be. For example, if the period of θ _L (t) is set to 1/n of the period of θ _R (t), the bright spot and the viewpoint overlap n times during one period of θ _R (t), so n Measurement points can be obtained.

The geometric configuration of the above-mentioned measurement method is shown in FIG. 2. In the figure, H is the leg of the perpendicular line drawn from the bright spot A to the ξ axis, and the coordinate of H is ξ _L. Moreover, I is a mapping of a bright spot by the lens L of the light receiver. In this way, the following formula holds true.

h=AH=dtanθ _L tanθ _R /tanθ _L +tanθ _R …(1) l _L =O _L A=dtanθ _R /cosθ _L (tanθ _L +tanθ _R )……(2) l _R =O _R A=dtanθ _L /cosθ _R (tanθ _L +tanθ _R )...(3) ξ _L = O _L H = dtanθ _R /tanθ _L + tanθ _R ...(4) Next, map I of the bright spot connected by the lens L of the photoreceiver. The relationship between the bright spot A and the bright spot A is illustrated in FIG. 3. The figure takes the center O _R of the lens L as the origin,
The direction of the optical axis is shown as the r-axis, and the p-axis is shown in the center plane of the lens. s is a light receiving element and its coordinates are r _s ,
I is a map of the bright spot and its coordinates are r _i , F is the light beam L
Let the coordinates of the focal point be r _f , and the coordinates of the bright spot A be -l _R . In this way, the following formula holds true.

l _R = r _i r _f / r _i -r _f ... (5a) or r _i = l _R - r _f / l _R -r _f ... (5b) r _f = f = focal length of lens L Photodetector If the distance r _s between s and the lens L can be adjusted, for example, using the values of θ _R (t) and θ _L (t) obtained with incomplete focus adjustment, h and l can be adjusted. Find the values of _L , l _R , ξ _L , and r _i , and if r _i is not equal to r _s , move the light-receiving element s and perform a second measurement as r _s → r _i to improve accuracy. It is possible to perform high-quality measurements. If measurements are repeated a third time and then a fourth time, the values will converge to an accurate value. In the case of Fig. 3, the focus adjustment is insufficient, so the bright spot is mapped to the coordinates p _s of the outer edge.
It is blurred between ~ p _s . Even in this case, it should be possible to obtain approximately accurate values by taking the center of the blurred mapping, but it is important to bring the light receiving element s close to the focal position in order to improve accuracy.

The same applies to focus adjustment of the projector. Fourth
As shown in the figure, the center O _L of the lens L _L of the projector is the origin, the optical axis is the r axis, the coordinates of the light source (photodiode, exit of an optical fiber, etc.) D _L are r _L , and the coordinates of the bright point A are −l _L , the focal point of the lens L _L has coordinates r _FL . If the focal length is correct, the light source is mapped to a bright spot, and the sharpest bright spot is obtained, and in this case, the following relationship holds true.

r _L = l _L r _FL /l _L −r _FL ...(6) r _FL = Focal length of the lens L _L of the projector If the direction of the light beam of the measurement head can be changed around O _L , then the formula ( 6) l _L in formula (3) is l _L
becomes the same as

Therefore, as in the case of the photoreceiver, r _L is calculated using l _L obtained from the direction of the light beam and the direction of the line of sight.
It becomes possible to calculate the r _L of the projector and adjust it to the correct value.

In addition, when performing measurements with the measuring head separated from the object to be measured by a substantially constant distance, for example, use equation (5b) to set l _R to a predetermined value, calculate r _i , and fix the light receiving element s to r _i . If l _R does not reach a predetermined value, the focus can be adjusted correctly by moving the entire measurement head and controlling l _R to a predetermined value.

Next, we define the direction of the light beam L _s and the direction of the line of sight L _r as periodic functions of time θ _L (t) and θ _R
An example of the configuration of a measurement system for determining the cross-sectional shape of the object to be measured by changing the position according to (t) and measuring the overlapping position of the viewpoint and the bright spot will be explained with reference to FIG. Fifth
The figure is just one example, and many similar variations can be considered.

In FIG. 5, the sine wave of frequency ν generated by the oscillator OSC is input to the light emitter L while being superimposed on the output of the DC supply device DC, and drives its light emitting element. A light beam L _s that has been sinusoidally modulated at a frequency ν is emitted from the projector, producing a bright spot A on the surface of the object to be measured. The bright spot A moves according to the light beam direction θ _L (t), and the viewpoint of the light receiver R moves according to the line-of-sight direction θ _R (t). The receiver has an optical bandpass filter L-FIL whose pass band is the wavelength band of the signal light, so if the bright spot and the viewpoint overlap, the light entering the receiver will be separated by the signal light and L-FIL. It becomes empty noise light. If the bright spot and the viewpoint do not overlap, the light that enters the photoreceiver becomes noise light that cannot be removed by the L-FIL.

The receiver produces an electrical output proportional to the input light.
After passing this electrical output through the amplifier AMP, it is split into two parts, and one of them is passed through a bandpass filter BPF whose passband is the frequency ν.The output of the BPF is as follows.
This results in a superposition of the sine wave component of frequency ν, that is, the signal component, and the noise component that could not be removed up to now. This is further combined with a detector DT and a low pass filter LPF.
Let the output obtained through the V _s (t) be V s (t). A band-rejection filter with the other side of the branch as a stop band
Let V _o (t) be the output obtained through BEF, detector DT, and low-pass filter LPF. In this way, V _s
(t) has a large value only when the bright spot and the viewpoint overlap, and has a small value representing the noise level when the bright spot and the viewpoint do not overlap. On the other hand, V _o (t)
is always the value of the noise level.

Therefore, V _s (t) and V _o (t) are put into the ratio measurement circuit RAT to obtain V _s (t)/V _o (t), and then V _s (t)/V _o (t) into the comparator CP _so , take {V _s (t)/V _o (t) - K}, and calculate {V _s
If the timing pulse is emitted when (t)/V _o (t)-K}0, the timing pulse will be emitted when the bright spot and the viewpoint overlap. K is a constant value determined experimentally. V _s
The input light (signal light + noise light) to the receiver R that produces V _o (t) and the input light (noise light) to the receiver R that produces V o (t) are both reflected light from the surface of the object to be measured.
The influence of the condition of the surface of the object to be measured on V _s (t)/V _o (t) is considerably reduced. LD and RD in the figure respectively drive the direction θ _L (t) of the light beam of the emitter and the direction θ _R (t) of the viewpoint of the receiver, and
This circuit outputs values in each direction and inputs them to sampling circuits S _L and S _R. When SP _L and SP _R receive the sampling pulse from the comparator CP _so , θ _L (t) and θ _R (t) respectively.
The value is sampled, digitized, and input to the microcomputer μ-COMP.

The microcomputer μ-COMP has θ _L (t) and θ _R (t)
When is input, according to equations (1) to (6) shown earlier,
h, l _L , l _R , ξ _L , r _i , r _L can be calculated.
FD _L and FD _R in Figure 5 are the focal length adjusters of the emitter and receiver, respectively, and FD _L is μ-COMP
Therefore, by accepting the value of r _L in equation (6) and adjusting the distance between the light source D _L of the projector and the lens L _L to r _L , the bright spot is made clear, and F _R is obtained from μ-COMP in equation (5). Accepting the value of r _i , the distance between the light receiving element s and the lens L is adjusted to r _i so that the image of the bright spot is clearly focused on the light receiving sensor. As can be seen from the above, in the measurement head of the present invention, the optical system, electrical measurement system, microcomputer, and focus adjustment mechanism form a feedback loop, so if there is sufficient time for measurement, focus adjustment can be performed. accurate measurements can be made. Furthermore, even if sufficient time is not available for measurement, fairly good measured values can be obtained if the surface of the object to be measured is smooth. Furthermore, a method of predicting the next focal length from past focal length measurements can also be used. It is suitable for automating work because it can continue measuring while automatically controlling the focal length to the correct value.

Until now, in order to change the direction of the line of sight θ _R (t) of the emitter, the entire receiver had to be rotated, but the receiver was configured using an optical bandpass filter,
Even if a lens and a light-receiving element array are used and the line-of-sight direction is changed by switching the light-receiving element output terminal in the light-receiving element array, the same method as described above can be applied.

As mentioned above, the measuring head of the present invention has the following remarkable features.

(i) By using modulated light as a light beam,
Measurement interference from noise light is greatly reduced, so
Measurement accuracy can be improved.

(ii) A control loop consisting of an optical system, an electrical measurement system, a microcomputer, and a focal length adjuster automatically and continuously adjusts the focus of the emitter and receiver, further improving measurement accuracy. There is.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an overview of the measuring head for a robot with a focus adjustment function of the present invention, Fig. 2 is a diagram showing the principle of the optical system of this measuring head, and Fig. 3 is a diagram showing the light receiving system of this measuring head. 4 is a diagram showing the light projection system of the main measurement head, and FIG. 5 is a diagram showing a specific example of the structure of the entire measurement system of the main measurement head. B is the main body of the measurement head, L is the emitter, R is the light receiver, ξ, η, ζ are the coordinate axes fixed to the measurement head, O _L is the origin, O _L and O _R are the light beams, respectively.
and the center of rotation of the viewpoint, L _s is the light beam, L _r is the line of sight of the receiver, J is the surface of the object to be measured, A is the bright spot created by the light beam on J, and L is the focusing lens of the receiver , I is the mapping in the photoreceiver of A, s is the photodetector, d
is the distance between the receiver and the emitter, d = _{L R} , l _L = _L
A, l _R = _R , AH is the length of the perpendicular from A to the ξ axis, ξ _L = _L , F is the focal point of the lens L of the receiver,
The origin of p and r is the center O _R of the lens of the optical receiver,
Coordinate system with the optical axis as the r axis, r _s , r _i , r _f are the position coordinates of the light-receiving element s, bright spot image I, and focal point F, respectively, and p _s and _-ps are when the bright spot image is blurred p coordinate of the outer edge of , D _L is the light source of the floodlight, F _L is the lens _L of the floodlight
The focal point of , r _L and r _FL are the position coordinates of D _L and F _L respectively,
OSC is an oscillator, DC is a direct current supply, L-FIL is an optical bandpass filter, AMP is an amplifier, BPF is a bandpass filter, DT is a detector, LPF is a low-pass filter, and V _s (t) is a signal. electrical power output, including a light component;
V _o (t) is the electrical output including noise, RAT is the ratio measurement circuit, CP _so is the comparator, K is a fixed value determined experimentally, SP _R , SP _L are the sampling circuits, and RD is the drive in the line-of-sight direction of the optical receiver. , display circuit, LD is the drive and display circuit for the light beam direction of the emitter, FD _L is the focal length adjuster for the emitter, _FDR is the focal length adjuster for the receiver, and μ-COMP is the microcontroller.

Claims (1)

[Claims] 1 Equipped with an emitter and a receiver installed at a certain distance apart, the light beam emitted by the emitter and the line of sight of the receiver are set within the same plane, but their directions are periodically changed, so that the light beam hits the surface of the object to be measured. The direction of the light beam and the direction of the line of sight when the line of sight of the receiver catches the bright spot to be created are input into the microcontroller.
At the same time as calculating the position of the bright spot, the amount necessary to adjust the focus of the emitter to correctly focus the bright spot of the emitter on the surface of the object to be measured, and the receiver to correctly focus the image of the bright spot on the light receiving element of the receiver. The amount required for focus adjustment is calculated, and these amounts are supplied as control signals to the emitter's focal length adjuster and the receiver's focal length adjuster, respectively, to adjust the focus of the emitter and receiver. A method for adjusting the focus of a measuring head for a robot, which is characterized by: