JPH086560B2 - Automatic segment assembly equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a segment automatic assembly apparatus for shield work, and more particularly to a relative position / posture of an assembly segment roughly positioned near the assembly position and an existing segment. When correcting the positioning of the assembly segment according to the deviation amount, one or both of the assembly segment and the existing segment is missing, and the positioning error or segment Destruction,
The present invention relates to means for preventing deformation and destruction of an erector body.

[Conventional technology]

When the segments are automatically assembled by the shield work, the inventors of the present invention use FIG. 3 (c) as means for detecting the deviation amount of the relative position / orientation between the assembly segment roughly positioned near the assembly position and the existing segment. It was previously proposed to adopt the light-section method as shown in ().
issue).

This uses three sets of floodlights and a TV camera arranged near the segment grip of the erector body, and uses three slit lights from each floodlight in the tunnel longitudinal direction and tunnel crossing direction of the existing segments 1a and 1b and the assembly segment 2. The respective slit light images A-A ', BB', and C-C 'shown in FIGS. 3 (a) and 3 (b) are imaged by the respective television cameras, and these televisions are irradiated. Image data from the camera is image processed and the end points a, a ′, b,
The coordinates of b ′, c, c ′ are calculated, and the deviation amount of the relative position / orientation between the existing segment 1a, 1b and the assembly segment 2 is calculated from the coordinate value, and the erector body is automatically operated based on the result. , The positioning of the assembly segment 2 is to be corrected.

[Problems to be solved by the invention]

The above proposal does not consider that an incorrect deviation amount is detected and calculated when one or both of the assembly segment and the existing segment is missing. FIGS. 3 (a) and 3 (b) show an example of a slit light image in a normal state in which the assembled segment and the existing segment have no defects. In these slit light images, ΔX ₁ , Δ
X ₂ , ΔY ₃ is the clearance between the segments, ΔY ₁ , ΔY
₂ and ΔX ₃ indicate steps, but if the assembly segment 2 is chipped as shown by 2a in FIG. 4 (c), the slit light image A is deformed as shown in FIG. 4 (a). , By detecting the end point a ₁ or a ₂ which is different from the normal time,
An incorrect deviation amount is calculated. When the positioning correction is performed based on this erroneous deviation amount, for example, when a ₁ is detected as the end point, the step ΔY ₁ becomes apparently large,
Positioning correction will not be performed completely, and a ₂
Is detected as an end point, the clearance ΔX ₁ is apparently large, so that the assembly segment 2 and the existing segment 1a collide with each other due to the positioning correction operation of the erector body, resulting in segment destruction, deformation of the erector body, and destruction. May invite you. The same problem occurs when the existing segments 1a and 1b are chipped.

It is an object of the present invention to prevent a problem caused by the above-described positioning correction based on an erroneous deviation amount even when one or both of the assembly segment and the existing segment is missing.

[Means for solving the problem]

In order to achieve the above object, the automatic segment assembly apparatus of the present invention is an erector body installed in a shield machine, a servo control apparatus for controlling the position / orientation of an assembly segment held by the erector body according to a command, and an operator. A manual operation device that outputs operation signals for the position and orientation of the assembly segment, and a projector that irradiates slit light to each boundary portion of the assembly segment and the existing segment roughly positioned near the predetermined assembly position in the tunnel crossing direction and tunnel longitudinal direction. And a television camera that captures a light-section image by the slit light, an image memory that captures image data obtained from these television cameras, and image processing of the data stored in the image memory to detect the end point coordinates of the light-section image. And the relative value of the assembly segment and the existing segment from the coordinate value A means for calculating the deviation amount of the position / orientation, a positioning correction control for instructing the servo control device to perform the positioning correction of the assembly segment based on the calculated deviation amount, and the position of the assembly segment by the operation signal from the manual operation device. A main body control device capable of switching manual control for controlling the posture is provided.

Further, the present invention sets the allowable range of the end point coordinates of the light-section image when both the assembled segment and the existing segment are normal as a threshold value in advance, and the detected end point coordinate value is the threshold value. When the coordinate value deviates from the threshold value, the main body control device stops the positioning correction control based on the deviation amount, and includes abnormality determination processing means for instructing to enter a manual control state. It is characterized by that.

[Action]

Since the invention according to claim 1 is configured as described above, for example, chipping or the like occurs in one or both of the assembly segment and the existing segment, and the deviation amount is calculated as an abnormally large value. In such a case, the positioning correction control of the assembly segment by the servo control device can be stopped and switched to the manual control by the manual operation device. As a result, it is possible to continue the assembly of the assembly segment by the manual operation of the operator without causing the positioning failure and the segment breakage due to the positioning correction control based on the erroneous deviation amount, the segment damage, and the deformation and destruction of the erector body.

Further, in the invention described in claim 2, when the coordinate value detected by the means for detecting the end point coordinates deviates from the preset threshold value, the main body control device is automatically operated by the instruction from the abnormality determination processing means. Stop the positioning correction control based on the deviation amount and switch to manual control. Therefore, as in the first aspect, it is possible to continue the assembly of the assembly segment by the manual operation of the operator without causing the positioning failure, the segment destruction, the erector body deformation, and the destruction due to the positioning correction control based on the incorrect deviation amount. it can.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIGS. 7 to 10, the erector body 12 used for automatic segment assembly is installed at the rear part of the shield body 11 having a cylindrical shape. The eclectic body 12 is roughly divided into an eclectic ring 13, which is a slewing mechanism, and a slewing motor 1.
6, hanging beam 21 and pressing jack 22, which is a pressing (heaving) mechanism, horizontal slide frame, which is a turning fine adjustment mechanism
24 and the lateral slide jack 25, the front and rear slide frame 27 and the front and rear slide jack 28 which are the front and rear sliding mechanisms, the spherical frame 29 which is the posture control mechanism for pitching, rolling, yawing and the like, and the posture control jacks 31, 32, 33 and the segments. It is composed of a grip portion 34.

The erector ring 13 is guided by the outer peripheral guide rollers 14 and the side guide rollers 15 arranged at a plurality of positions on the shield body 11, and is rotatably driven by a slewing motor 16 attached to the shield body 11 via a pinion 17 and a ring gear 18. It Along with this, the following respective parts supported on the elector ring 13 are also turned left and right at the same time.

Guide rods 20 are attached to the left and right arms 19 of the electret ring 13.
The suspension beam 21 supported via the support beam 21 is moved in the heaving direction (Z-axis direction) by expansion and contraction of the pressing jack 22 mounted between the suspension beam 21 and the arm 19. Each part of also moves in the same direction.

The horizontal slide frame 24 supported by the suspension beam 21 via the linear bearing 23 is laterally slid on the suspension beam 21 in the Y-axis direction by expansion and contraction of the horizontal slide jack 25 mounted between the suspension beam 21 and the suspension beam 21, Along with this, the following parts supported on the horizontal slide frame 24 also move in the same direction. This movement is used for fine adjustment of the turning direction of the segment grip 34.

The front-rear slide frame 27 supported by the horizontal slide frame 24 via the linear bearing 26 is a front-rear slide jack 28 mounted between the front and rear slide frames 24.
By the expansion and contraction of the front and rear, it is slid back and forth on the horizontal slide frame 24 in the X-axis direction.
The following parts supported above also move in the same direction.

The spherical frame 29 incorporated in the spherical guide portion 27a of the front-rear slide frame 27 causes the two attitude control jacks 31 and 32 mounted between the front-rear slide frame 27 and the front-rear slide frame 27 to contract to make the following movements. In FIG. 9, 2
When the jacks 31 and 32 of the book are simultaneously extended or contracted, the spherical frame 29 is tilted in the direction of the arrow θ in FIG. 7 around the X axis including the spherical center G, and this movement causes the rolling control of the segment grip 34. Used for. When one of the jacks 31 and 32 is extended and the other is contracted, the spherical frame 29 is rotated left and right in the arrow Ψ direction of FIG. 9 around the Z axis including the spherical center G. The movement is used for yawing control of the segment grip 34.

The segment gripping portion 34 suspended from the central axis 30 of the spherical frame 29 is expanded and contracted by the attitude control jack 33 mounted between the spherical frame 29 and the spherical frame 29 in the direction of the arrow φ in FIG. 8 around the central axis 30. The movement is tilted, and this movement is used for pitching control of the segment grip portion 34.

The segment grip 34 includes a male threaded screw shaft 36 that matches the grout hole 35 of the assembly segment 2. Further, the segment grip portion 34 is equipped with a drive motor 37 for rotating the screw shaft 36, and an elevating jack 39 for elevating the screw shaft 36 together with the drive motor 37 and the bearing bracket 38. After aligning the screw shaft 36 with the grout hole 35 of the assembly segment 2 placed under the erector, the screw shaft 36 is projected toward the segment 2 while rotating the screw shaft 36, and after screwing into the grout hole 35, the segment 2 is By pulling back the screw shaft 36 until it hits the end surface of the segment grip portion 34, gripping of the segment is completed.

The erector body 12 is configured as described above, and has a function of gripping the assembly segment 2 and positioning it at a predetermined assembly position, and assembling it to the existing segment 1 by a bolt fastening device (not shown).

When assembling segments automatically, positioning of the assembled segment is performed by setting the target position from the measurement results of the position and orientation of the existing segment and numerically controlling the erector body 12, but there are measurement errors and control errors. ,
Actually, after the assembled segment is roughly positioned near the predetermined assembly position by the erector body 12, the existing segment 1
It is necessary to detect the deviation amount of the relative position / orientation of the assembly segment 2 and to perform the positioning correction. In order to perform this positioning correction, the deviation amount detecting means adopted in the present invention is first
Shown in the figure.

In FIG. 1, 1a and 1b are existing segments, and 2 is an assembly segment which is joined to the existing segment by bolts or the like. As shown in this figure, when the assembly segment 2 is roughly positioned near the predetermined assembly position, three slit lights from the projectors 3a, 3b, 3c are included, two of which are the existing segment 1a and the assembly segment. At the boundary in the tunnel longitudinal direction of No. 2, the other one irradiates the boundary between the existing segment 1b and the assembled segment 2 in the transverse direction of the tunnel, respectively, and each slit light image (hereinafter referred to as a light section image) A- A ', B-
B ', C-C' are imaged by the television cameras 4a, 4b, 4c.
As shown in FIG. 11, three sets of visual devices 43a, 43b, 43c in which these projectors and a television camera are integrated are provided near the segment grip 34 of the erector body 12.

The image data from the television cameras 4a, 4b, 4c are selected by the camera switch 5 and stored in the image memory 7 via the image input / output device 6, and the contents of the image memory 7 are stored in the image input / output device 6. It is displayed via the image monitor 8.

The arithmetic unit 9 image-processes the data stored in the image memory 7 to obtain the coordinates of the end points of each light section image, and the relative positions of the existing segments 1a, 1b and the assembly segment 2 are calculated from the coordinate values. The deviation amount of the posture is calculated and output to the control device (main body control device) 10 of the erector main body. Further, the arithmetic unit 9 compares the coordinate value with a threshold value, and if the coordinate value deviates from the preset threshold value, the allowable range of the end point coordinates when both the assembled segment and the existing segment are normal. , A command to switch to manual control
It also has an abnormality determination processing function that outputs to 10.

The main body control device 10 determines whether to perform the seventh operation based on the calculated deviation amount.
Position / posture control jacks 22, 25, 28, 3 shown in Figs.
Stroke amount necessary for positioning correction of 1, 32, 33 is calculated, positioning correction control for instructing a servo control device (not shown), and operation signals from the manual operation device 40 are used to operate the jacks 22 to 33 to assemble segment Position of·
It is configured so that manual control for controlling the attitude can be switched, and numerical control for rough positioning is also performed by a command from the main body control device 10.

The servo control device executes servo control of the jack stroke speed according to a command from the main body control device 10.

Image processing, end point coordinate calculation, deviation amount calculation, abnormality determination processing and the like in the arithmetic unit 9 will be described in detail below.

As shown in the display images of FIGS. 3 (a) and 3 (b), the three light-section images are the slit light images A and A'of two slits, respectively.
It is input as B, B'C, C '. In these light section images,
ΔX ₁ , ΔX ₂ , and ΔY ₃ represent the clearance between the segments by Δ
Y ₁ , ΔY ₂ , and ΔX ₃ represent steps.

The calculation algorithm of the calculation device 9 will be described with reference to FIG. 13. First, according to a normal image processing method, each image data is binarized, and only the slit light portion is divided into white and the others (step 51). ). Since this binary image is replaced with the original image in the image memory 7, by scanning the image memory, the end points a, a ', b, b', c, c'of the respective light section images are displayed on the image memory. The coordinates at are obtained (step 52).

In this embodiment, after the segment gripping is completed,
12 and the assembly segment 2 are in a state of being integrated with each other via the segment grip portion 34. Also, as shown in FIG.
Visual devices 43a, 43b, 43 that integrate a floodlight and a TV camera
Since c is mounted near the segment gripping device 34, the relative positional relationship between the visual devices 43a, 43b, 43c and the assembly segment 2 can be considered unchanged.

Therefore, the relative position / orientation of the existing segments 1a, 1b and the assembly segment 2 will be determined using the coordinate system (X, Y, Z) as shown in FIG.

The origin O of the X, Y, Z coordinates is taken as the end point of the assembly segment 2, and the end points of the light section image are set as a, a ', b, b', c, c ', respectively, and the points of these points on the image memory are set. Coordinate is a (P _ax , P _ay ).
a ′ (P _ax ′, P _ay ′), b (P _bx , P _by ), b ′ (P _bx ′,
P _by ′), c (P _cx , P _cy ), and c ′ (P _cx ′, P _cy ′). The absolute coordinates of each point with respect to the X, Y, Z coordinate system are
_{x, a y, a z)} , a '(a x', a y ', a z'), b (b x, b y,
_{b z), b '(b} x', b y ', b z'), c (c x, c y, c z),
_Let c ′ (c _x ′, _cy ′, _cz ′).

As it is apparent from Figure 5 _{a x = 0, a y =} l a, a z = 0,
_{b x = 0, b y =} l b, b z = 0, c x = l c, is _{c y = 0, c z =} 0. Here, l _a , l _b , and l _c are distances from the coordinate origin to the end points a, b, and c, which are constants uniquely determined when the visual device is installed.

Also, using the coordinates on the image memory, a _x = (P _ax −P _ax ′) · ΔP, a _y ′ = (P _ay −P _ay ) · ΔP +
l _a , a _z ′ = (P _ay −P _ay ′) · ΔP · tan ζ, b _x ′ = (P _bx −
P _bx ′) · ΔP, b _y ′ = (P _by −P _by ′) · ΔP + l _b , b _z ′
= (P _by -P _by ′) · ΔP · tan ζ, c _x ′ ＝ (P _cx ,
P _cx ′), ΔP + l _c , c _y ′ = (P _cy −P _cy ′) · ΔP, c _z ′
= (P _cy , -P _cy ′) · ΔP · tan ζ. Where ΔP
Is the length per pixel on the image memory, and ζ is the incident angle of the slit light with respect to the assembled segment (see FIG. 6).

In FIG. 6, the slit light from the projector 3 is incident on the assembly segment 2 at an angle ζ. When the intersection of the slit light and the inner surface of the assembly segment is O, the imaging lens 41 and the image sensor 42 of the television camera 4 are arranged on the normal line of the intersection O, and the image of the intersection O is formed at the point D on the sensor surface. Be done. Further, when the intersection point O ′ of the slit light and the inner surface of the existing segment 1 is set, the image of the intersection point O ′ is connected to the point E on the sensor surface.

From the relationship between the coordinates of each point on the image memory and the absolute coordinates of each point as described above, the deviation amounts ΔX, ΔY, ΔZ, φ, θ of the six items shown in FIGS. Ψ is obtained as follows. That is, the yawing amount _{Ψ tanΨ = (b x '-a} x') / (b y '-
a _y ′), rolling amount θ tan θ = (b _z -a _z ′) /. (b _y ′ −
a _y ′), the pitching amount φ is tan φ (c _z ′ −a _z ′) /
It is calculated as (c _x ′ −a _x ′). The amounts of sliding, turning, and heaving can also be obtained for each of the three points. Considering after correcting the amounts of yawing, rolling, and pitching, the amount of sliding ΔX is ΔX = a _x ′, and the amount of turning ΔY is ΔY. = C _y ′, the heaving amount ΔZ becomes a value represented by ΔZ = b _z ′.

Here, since the relative positional relationship between the visual devices 43a, 43b, 43c and the assembly segment 2 is unchanged, both the assembly segment 2 and the existing segments 1a, 1b are not missing. The coordinate values P _ax , P _ay , P _bx , P _by , P _cx , P _cy of the a, b, c on the image memory are values having a certain fixed width. Assuming that this width is ± Δr, C _ax −Δr ≦ P _ax ≦ C _ax + Δr …… (1) C _ay −Δr ≦ P _ay ≦ C _ay + Δr ………… (2) C _bx −Δr ≦ P _bx ≦ C _bx + Δr ……… (3) C _by −Δr ≦ P _bx ≦ C _bx + Δr ……… (4) C _cx −Δr ≦ P _cx ≦ C _cx + Δr ……… (5) C _cy −Δr ≦ P _cy ≦ C _cy + Δr (6) However, C _ax , C _ay , C _bx , C _by , C _cx , C _cy are constant values on each image memory. Also, the assembly segment 2 is roughly positioned near the assembly position. In this case, both the assembled segment 2 and the existing segments 1a and 1b are not missing. If they are normal, the deviation amount of the relative position / posture of these segments is a value with a certain width. The coordinate values P _ax ′, P _ay ′, P _bx ′, P _by ′ of the side end points a ′, b ′, c ′ on the image memory,
P _cx ′ and P _cy ′ are also values having a certain fixed width.
If this width is ± Δr ′, C _ax ′ −Δr ′ ≦ P _ax ′ ≦ C _ax ′ + Δr ′ ... (7) C _ay ′ −Δr ′ ≦ P _ay ′ ≦ C _ay ′ + Δr ′ ... (8) C _bx ′ −Δr ′ ≦ P _bx ′ ≦ C _bx ′ + Δr ′ ... (9) C _by ′ −Δr ′ ≦ P _bx ′ ≦ C _bx ′ + Δr ′… (10) C _cx ′ −Δr ′ ≦ P _cx ′ ≦ C _cx ′ + Δr ′ (11) C _cy ′ −Δr ′ ≦ P _cy ′ ≦ C _cy ′ + Δr ′ (12) where C _ax ′, C _ay ′, C _bx ′, C _by ′, C _cx ′ , C _cy ′
Can be expressed as a constant value in each image memory. That is, the respective end point coordinates cannot deviate from the threshold values represented by the left and right two terms of the above equations (1) to (12).

However, as shown in FIG. 4 (c), the assembly segment 2
If either or both of the existing segments 1a and 1b are missing, the slit light image will be deformed as shown in FIG. 7 (a), and the end point coordinates on the image memory will be compared with those when normal. It will change greatly.

Therefore, in this embodiment, it is sequentially checked whether or not the detected end point coordinates satisfy the above conditions (1) to (12) in the "comparison of end point coordinates and threshold value" in step 53 shown in FIG. However, if all are not satisfied, a manual control switching command is output (step 54). If the conditions are satisfied for all the image data from the television cameras 4a to 4c, the process proceeds from step 55 to step 56, the deviation amount calculation described above is performed, and the result is output to the main body control device 10.

FIG. 14 shows a control algorithm of the main body control device 10.
The main body control device 10 determines whether or not there is a manual control switching command (step 61), and if there is a manual control switching command, performs manual control (step 62),
If not, the above-described positioning correction control (step 63) is performed based on the deviation amount calculated by the arithmetic unit 9.

When the mode is switched to the manual control, this is displayed on the display screen or the like of the main body control device 10 so that the operator knows the abnormality and the assembly segment can be positioned by the manual scanning.

In FIG. 13, steps 51 and 52 are end point coordinate detection means, steps 53 and 54 are abnormality determination processing means, and step 55.
Correspond to deviation amount calculating means, respectively.

In the above embodiment, the main body control device 10 of the arithmetic unit 9 is separately provided, but one control computer may be provided with both functions.

In the above-described embodiment, the servo control and the manual control are switched depending on the determination result of the abnormality determination processing means. However, depending on the situation of the slit light image displayed on the image monitor 8, the correction may be performed. If the deviation amount does not converge to a predetermined amount or less even after repeated repetition, a means for making an operator judgment and forcibly switching from servo control to manual control may be provided.

〔The invention's effect〕

According to the present invention, one or both of the assembled segment and the existing segment are missing, and the deviation amount of the relative position / orientation between the assembled segment and the existing segment cannot be accurately detected / calculated from the end point coordinates of the light section image. In this case, since the main body control device can stop the positioning correction control based on the deviation amount and switch to the manual control state, the positioning correction based on the incorrect deviation amount can cause misalignment, segment destruction, or deformation of the erector main body. Destruction can be prevented in advance.

[Brief description of drawings]

FIG. 1 is a schematic diagram of the present invention, FIG. 2 is a system configuration diagram of an embodiment of the present invention, FIG. 3 is a diagram showing a light section image and its positional relationship in a normal state, and FIG. 4 is an assembly segment. FIG. 5 is an explanatory view of a segment coordinate system, FIG. 6 is an explanatory view of a visual device used in the present invention, and FIG. 7 is installed in a shield machine. FIG. 8 is a front view in which a part of the removed erector body is cut, and FIG.
-VIII sectional view, FIG. 9 is a sectional view taken along the line IX-IX of FIG. 7, FIG. 10 is a sectional view taken along the line XX of FIG. 7, and FIG. Shown in perspective view, twelfth
Figure is an explanatory diagram of the position / orientation deviation amount of the segment.Figure 13 is a flowchart showing the calculation algorithm of the calculation device.
FIG. 14 is a flowchart showing the control algorithm of the main body control device. 1a, 1b ... Existing segment, 2 ... Assembly segment, 3a, 3b, 3
c ... Projector, 4a, 4b, 4c ... TV camera, 7 ... Image memory, 9 ... Arithmetic device, 10 ... Main body control device, 11 ... Shield body, 12 ... Elector body, 34 ... Segment gripping part, 40 ... Manual operation device , 51, 52 ... Steps corresponding to the end point coordinate detection means 53, 54 ... Steps corresponding to the abnormality determination processing means, 55 ... Steps corresponding to the deviation amount calculation means, A-
A ', BB', C-C '... Light section image.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Hashimoto 650 Kuchidachi-cho, Tsuchiura-shi, Ibaraki Hitachi Construction Machinery Co., Ltd. Tsuchiura factory (72) Inventor Hiroaki Tokaibayashi 650 Kintate-cho, Tsuchiura-shi, Ibaraki Hitachi Construction Machinery Co., Ltd. Ceremony Company Tsuchiura Plant (72) Inventor Masakatsu Fujie 502 Kuritachi Machinery Research Center, Tsuchiura City, Ibaraki Prefecture Hiritsu Manufacturing Co., Ltd. (72) Inventor Yoshio Nakajima 502 Jinritsu Town, Tsuchiura City, Ibaraki Prefecture Hiritsu Manufacturing Machinery Co., Ltd. In the laboratory (56) Reference JP-A-1-263509 (JP, A) JP-A-2-24497 (JP, A) JP-A-4-213699 (JP, A) JP-A-4-83098 (JP, A) )

Claims (2)

[Claims] 1. A position of an erector body installed in a shield machine and a position of an assembly segment gripped by the erector body.
Servo control device that controls the posture according to commands, manual operation device that outputs the operation signal of the position and posture of the assembly segment by the operator, tunnel segment between the rough-positioned assembly segment and existing segment near the predetermined assembly position, and tunnel A light projector that irradiates each boundary in the longitudinal direction with slit light, a television camera that captures a light-section image by the slit light, an image memory that captures image data obtained from these television cameras, and data stored in the image memory. Means for image processing to detect the end point coordinates of the light section image, means for calculating the deviation amount of the relative position / orientation of the assembly segment and the existing segment from the coordinate values, and the assembly segment based on the calculated deviation amount. Positioning correction control for instructing the servo controller to perform the positioning correction of Segment automatic assembling apparatus being characterized in that a switching of the manual control for controlling the position and orientation of the assembled segments can body control unit by the operation signal from Yuaru operating device. 2. An allowable range of end point coordinates of the light-section image when both the assembled segment and the existing segment are normal is set as a threshold value in advance, and the detected end point coordinate value is set as the threshold value. In comparison, when the coordinate value deviates from the threshold value, the main body control device is provided with an abnormality determination processing means for instructing to stop the positioning correction control based on the deviation amount and enter the manual control state. A segment automatic assembly device characterized by the above.