阅读说明：本技术 冷轧板板型检测系统及方法、冷轧板板型控制方法 (Cold-rolled sheet profile detection system and method and cold-rolled sheet profile control method ) 是由 张利伟 陈涛 郑州 于 2018-08-31 设计创作，主要内容包括：本发明公开了一种冷轧板板型检测系统及方法、冷轧板板型控制方法。该冷轧板板型检测系统,包括安装在冷轧板轧机的床身上的激光器、测距传感器、液压尾座、推杆、目标测量靶和摄像头,其中,摄像头和液压尾座分别安装在床身的两端,激光器安装在摄像头与液压尾座之间,目标测量靶通过推杆与液压尾座相连,目标测量靶的中心与激光器的中心之间的连线与床身所在直线平行。本发明应用于冷轧板冷轧过程。(The invention discloses a cold-rolled sheet profile detection system and method and a cold-rolled sheet profile control method. The cold-rolled sheet plate type detection system comprises a laser, a distance measuring sensor, a hydraulic tailstock, a push rod, a target measurement target and a camera, wherein the laser, the distance measuring sensor, the hydraulic tailstock, the push rod, the target measurement target and the camera are installed on a bed body of a cold-rolled sheet rolling mill, the camera and the hydraulic tailstock are installed at two ends of the bed body respectively, the laser is installed between the camera and the hydraulic tailstock, the target measurement target is connected with the hydraulic tailstock through the push rod, and a connecting line between the center of the target measurement target and the center of the laser is parallel to a straight line. The invention is applied to the cold rolling process of cold-rolled sheets.)

1. The utility model provides a cold-rolled sheet board type detecting system, its characterized in that, is including installing laser instrument, hydraulic pressure tailstock, push rod, target measurement target and the camera on the lathe bed of cold-rolled sheet rolling mill, wherein, the camera with hydraulic pressure tailstock installs respectively the both ends of lathe bed, the laser instrument is installed the camera with between the hydraulic pressure tailstock, the target measurement target passes through the push rod with hydraulic pressure tailstock links to each other, the center of target measurement target with line between the center of laser instrument with the lathe bed is parallel to the horizontal direction is last.

2. The cold-rolled sheet profile detection system of claim 1, wherein the hydraulic tailstock comprises a vertical hydraulic column, a horizontal hydraulic column, a sliding plate and a supporting plate, wherein one end of the vertical hydraulic column is mounted on the lathe bed, the sliding plate is mounted at the other end of the vertical hydraulic column, the supporting plate is mounted above the sliding plate, the horizontal hydraulic column is mounted between the sliding plate and the supporting plate and connected with the supporting plate, and one surface of the supporting plate, which is far away from the horizontal hydraulic column, is connected with the push rod.

3. The cold-rolled sheet profile detecting system according to claim 1, further comprising a distance measuring sensor installed on the bed, wherein the distance measuring sensor is located on a side of the hydraulic tailstock away from the push rod, and a connecting line between a center of the target measuring target and a center of the distance measuring sensor is parallel to the bed in a horizontal direction.

4. The cold-rolled sheet profile inspection system of claim 1, wherein said laser is a focused laser.

5. The cold-rolled sheet profile detection system of claim 1, wherein said camera is a high-definition camera.

6. The cold-rolled sheet profile detecting system according to claim 1, further comprising a control host, wherein the control host is wirelessly connected to the laser.

7. A cold-rolled sheet profile detection method is characterized by comprising the following steps:

detecting by using the cold-rolled sheet profile detection system according to claim 1 to obtain the profile fluctuation variation on the cold-rolled sheet strip;

and obtaining the plate shape defects of the cold-rolled plate strip according to the plate shape fluctuation variable quantity.

8. The method for detecting the cold-rolled sheet profile according to claim 7, wherein the step of detecting by using the cold-rolled sheet profile detecting system according to claim 1 to obtain the profile fluctuation variation on the cold-rolled sheet strip comprises the following steps:

obtaining the arch height and the arch distance of the arch on the cold-rolled sheet strip through a laser in the cold-rolled sheet strip shape detection system;

obtaining the wave height and the wave distance of the edge waves on the cold-rolled plate strip through the laser;

obtaining the wave height and the wave distance of the medium waves on the cold-rolled plate strip through the laser;

and obtaining the plate shape fluctuation variation quantity on the cold-rolled plate strip according to the arch height and the arch distance, the wave height and the wave distance of the side waves and the wave height and the wave distance of the middle waves.

9. A cold-rolled sheet profile control method is characterized by comprising the following steps:

the cold-rolled sheet profile detection method of claim 7 is used for detection, the profile defect parameter S of the cold-rolled sheet strip is obtained, and the bow component Z on the cold-rolled sheet strip is obtained₁Middle wave component Z₂Sum edge wave component Z₃；

According to said plate type defect parameter S, said bow component Z₁The middle wave component Z₂And said edge wave component Z₃Obtaining a bow component coefficient R₁Middle wave component coefficient R₂Sum edge wave component coefficient R₃Wherein, in the step (A),

according to the bow component coefficient R₁The coefficient of the middle wave component R₂And the edge wave component coefficient R₃And adjusting the operating parameters of the cold-rolled sheet rolling mill and controlling the cold-rolled sheet profile.

10. The cold-rolled sheet profile control method according to claim 9, wherein the bow component coefficient R is determined according to the bow component coefficient R₁The coefficient of the middle wave component R₂And the edge wave component coefficient R₃Adjusting the operating parameters of the cold-rolled sheet rolling mill, and controlling the sheet profile of the cold-rolled sheet comprises the following specific steps:

the bow component coefficient R₁Adjusting the roll inclination of the cold-sheet rolling mill as a roll inclination control correction value;

the coefficient R of the middle wave component₂Adjusting the bending roll of the cold-rolled sheet rolling mill as an automatic correction value of the bending roll control;

dividing the edge wave componentCoefficient R₃And adjusting the intermediate roll of the cold-rolling sheet mill as an intermediate roll control automatic correction value.

Technical Field

The invention relates to the technical field of cold rolling, in particular to a cold-rolled sheet profile detection system and method and a cold-rolled sheet profile control method.

Background

The cold-rolled plate is a steel plate with the thickness less than 4mm, which is formed by hot-rolling a common carbon structural steel strip and further cold-rolling the common carbon structural steel strip. Because rolling at normal temperature does not produce scale, the cold plate has good surface quality and high dimensional precision, and the mechanical property and the processing property of the cold plate are superior to those of a hot rolled thin steel plate by annealing treatment, and the cold plate is gradually used for replacing the hot rolled thin steel plate in many fields, particularly the field of household appliance manufacturing.

At present, in the production process of cold-rolled sheets, there are high requirements on the flatness of cold-rolled sheets such as automobile steel sheets, tin-plated steel sheets, silicon steel sheets, aircraft aluminum sheets and the like, but the flatness is not only one of the important properties of cold-rolled products, but also very important for the rolling process itself. When the strip is rolled on the strip which is not straight in the width direction of the strip, the tension distribution unevenness in the width direction is increased, so that the strip is broken, and the yield of the cold-rolled sheet is reduced. Therefore, in the production of thin cold-rolled sheets, the strip shape control is an indispensable link.

Disclosure of Invention

The invention aims to provide a cold-rolled sheet profile detection system and method and a cold-rolled sheet profile control method, which are used for detecting and controlling the profile of a cold-rolled sheet, avoiding strip breakage and improving the yield of the cold-rolled sheet.

In order to achieve the purpose, the invention provides a cold-rolled sheet plate type detection system which comprises a laser, a hydraulic tailstock, a push rod, a target measurement target and a camera, wherein the laser, the hydraulic tailstock, the push rod, the target measurement target and the camera are arranged on a bed body of a cold-rolled sheet rolling mill, the camera and the hydraulic tailstock are respectively arranged at two ends of the bed body, the laser is arranged between the camera and the hydraulic tailstock, the target measurement target is connected with the hydraulic tailstock through the push rod, and a connecting line between the center of the target measurement target and the center of the laser is parallel to the bed body in the horizontal direction.

Optionally, the hydraulic tailstock includes a vertical hydraulic column, a horizontal hydraulic column, a sliding plate, and a supporting plate, wherein one end of the vertical hydraulic column is installed on the lathe bed, the other end of the vertical hydraulic column is installed on the sliding plate, the supporting plate is installed above the sliding plate, the horizontal hydraulic column is installed between the sliding plate and the supporting plate and connected to the supporting plate, and one surface of the supporting plate far away from the horizontal hydraulic column is connected to the push rod.

Optionally, the cold-rolled sheet profile detection system still includes and installs range sensor on the lathe bed, range sensor is located hydraulic tailstock keeps away from one side of push rod, just the line between the center of target measurement target with range sensor's center with the lathe bed is parallel in the horizontal direction.

Optionally, the laser is a focused laser.

Optionally, the camera is a high-definition camera.

Optionally, the cold-rolled sheet profile detection system further comprises a control host, and the control host is wirelessly connected with the laser.

The invention also provides a cold-rolled sheet profile detection method, which comprises the following steps:

detecting by using the cold-rolled sheet strip detecting system to obtain the strip fluctuation variation on the cold-rolled sheet strip;

and obtaining the plate shape defects of the cold-rolled plate strip according to the plate shape fluctuation variable quantity.

Optionally, the detecting by using the cold-rolled sheet strip shape detecting system includes the specific steps of:

obtaining the arch height and the arch distance of the arch on the cold-rolled sheet strip through a laser in the cold-rolled sheet strip shape detection system;

obtaining the wave height and the wave distance of the edge waves on the cold-rolled plate strip through the laser;

obtaining the wave height and the wave distance of the medium waves on the cold-rolled plate strip through the laser;

and obtaining the plate shape fluctuation variation quantity on the cold-rolled plate strip according to the arch height and the arch distance, the wave height and the wave distance of the side waves and the wave height and the wave distance of the middle waves.

The invention also provides a cold-rolled sheet profile control method, which comprises the following steps:

the cold-rolled sheet strip shape detection method is used for detection to obtain the sheet shape defects of the cold-rolled sheet stripParameter S, and bow component Z on the cold-rolled sheet strip₁Middle wave component Z₂Sum edge wave component Z₃；

According to said plate type defect parameter S, said bow component Z₁The middle wave component Z₂And said edge wave component Z₃Obtaining a bow component coefficient R₁Middle wave component coefficient R₂Sum edge wave component coefficient R₃Wherein, in the step (A),

；

according to the bow component coefficient R₁The coefficient of the middle wave component R₂And the edge wave component coefficient R₃And adjusting the operating parameters of the cold-rolled sheet rolling mill and controlling the cold-rolled sheet profile.

Optionally, according to the bow component coefficient R₁The coefficient of the middle wave component R₂And the edge wave component coefficient R₃Adjusting the operating parameters of the cold-rolled sheet rolling mill, and controlling the sheet profile of the cold-rolled sheet comprises the following specific steps:

the bow component coefficient R₁Adjusting the roll inclination of the cold-sheet rolling mill as a roll inclination control correction value;

the coefficient R of the middle wave component₂Adjusting the bending roll of the cold-rolled sheet rolling mill as an automatic correction value of the bending roll control;

the coefficient R of the edge wave component is obtained₃And adjusting the intermediate roll of the cold-rolling sheet mill as an intermediate roll control automatic correction value.

After the scheme is adopted, the invention has the following beneficial effects:

the invention provides a cold-rolled sheet plate shape detection system, which comprises a laser, a hydraulic tailstock, a push rod, a target measurement target and a camera, wherein the laser, the hydraulic tailstock, the push rod, the target measurement target and the camera are arranged on a bed body of a cold-rolled sheet rolling mill, the camera and the hydraulic tailstock are respectively arranged at two ends of the bed body, the laser is arranged between the camera and the hydraulic tailstock, the target measurement target is connected with the hydraulic tailstock through the push rod, and a connecting line between the center of the target measurement target and the center of the laser is parallel to the bed body in the horizontal direction, so that in the rolling process of a cold-rolled sheet strip, the target measurement target can be ensured to move on the cold-rolled sheet strip along with the movement of a roller through the hydraulic tailstock and the push rod, and on the one hand, the moving track of the target measurement target can be observed through the camera; on the other hand, the movement amount of the target measuring target is measured by a laser installed between the camera and the hydraulic tailstock while observing or after the cold-rolled sheet strip is observed to have the sheet type defect, so that the fluctuation variation of the sheet type on the cold-rolled sheet strip is obtained, the sheet type defect parameter of the cold-rolled sheet strip and each component related to the sheet type defect parameter are obtained, and finally, the operation parameter of the cold-rolled sheet rolling mill can be obtained and adjusted according to the sheet type defect parameter and each component related to the sheet type defect parameter, so that the sheet type of the cold-rolled sheet is controlled, the phenomenon that the cold-rolled sheet has the broken strip is avoided, and the yield of the cold-rolled sheet is improved.

Drawings

FIG. 1 is a schematic structural diagram of a cold-rolled sheet profile detection system provided by the present invention;

FIG. 2 is a schematic structural diagram of a hydraulic tailstock provided by the present invention;

FIG. 3 is a flow chart of a cold-rolled sheet profile detection method according to the present invention;

FIG. 4 is a flow chart of a cold-rolled sheet profile control method provided by the invention.

Reference numerals:

1, a lathe bed; 2-a laser; 3-hydraulic tailstock;

4, a push rod; 5-target measurement target; 6, a camera;

7-a carriage; 8-a nut; 9-a lead screw;

10, a motor; 11-a coupler; 12-a slide rail;

13-a base; 31-vertical hydraulic column; 32-horizontal hydraulic column;

33-a slide plate; 34-a pallet.

Detailed Description

The invention will be elucidated on the basis of an embodiment shown in the drawing. The embodiments disclosed herein are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is not limited to the following description of the embodiments, but is defined only by the scope of the claims, and includes all modifications having the same meaning as and within the scope of the claims.

The structure of the cold-rolled sheet profile detection system provided by the invention is described below with reference to specific embodiments.

As shown in fig. 1, the cold-rolled sheet profile detection system provided by the invention comprises a laser 2, a hydraulic tailstock 3, a push rod 4, a target measurement target 5 and a camera 6, which are arranged on a bed body 1 of a cold-rolled sheet rolling mill. Specifically, a camera 6 and a hydraulic tailstock 3 are respectively installed at two ends of the lathe bed 1, a laser 2 is installed between the camera 6 and the hydraulic tailstock 3, a target measuring target 5 is connected with the hydraulic tailstock 3 through a push rod 4, and a connecting line between the center of the target measuring target 5 and the center of the laser 2 is parallel to the lathe bed 1 in the horizontal direction.

Illustratively, in the process of rolling a cold-rolled sheet strip on a cold-rolled sheet rolling mill, because the target measuring target 5 is connected with the hydraulic tailstock 3 through the push rod 4, in the moving process of the roller, the target measuring target 5 can be ensured to move on the cold-rolled sheet strip along with the movement of the roller through the action of the hydraulic tailstock 3 and the push rod 4, and then, on one hand, the moving track of the target measuring target 5 can be observed through the camera 6, so as to judge the sheet profile condition of the cold-rolled sheet strip and judge whether the sheet profile defect occurs on the cold-rolled sheet strip; on the other hand, it is also possible to obtain the sheet type defect parameter of the cold rolled sheet strip and the respective components relating to the sheet type defect parameter by measuring the amount of movement of the target measuring target 5 by the laser 2 installed between the camera 6 and the hydraulic tailstock 3 at the same time or after the occurrence of the sheet type defect of the cold rolled sheet strip is observed, and obtaining the amount of fluctuation of the sheet type on the cold rolled sheet strip.

The cold-rolled sheet profile detection system provided by the embodiment of the invention comprises a laser 2, a hydraulic tailstock 3, a push rod 4, a target measuring target 5 and a camera 6 which are arranged on a lathe body 1 of a cold-rolled sheet rolling mill, wherein, the camera 6 and the hydraulic tailstock 3 are respectively arranged at two ends of the lathe bed 1, the laser 2 is arranged between the camera 6 and the hydraulic tailstock 3, the target measuring target 5 is connected with the hydraulic tailstock 3 through the push rod 4, the connecting line between the center of the target measuring target 5 and the center of the laser 2 is parallel to the lathe bed 1 in the horizontal direction, so that in the rolling process of the cold-rolled sheet strip, the movement of the target measuring target 5 on the cold-rolled sheet strip following the movement of the roll can be ensured by means of the hydraulic tailstock 3 and the push rod 4 which, on the one hand, the moving track of the target measuring target 5 can be observed through the camera 6 at the other end of the lathe bed 1, and then whether the cold-rolled sheet strip has a sheet type defect or not is judged; on the other hand, the movement amount of the target measuring target 5 is measured by the laser 2 installed between the camera 6 and the hydraulic tailstock 3 while or after the occurrence of the slab type defect of the cold-rolled sheet strip is observed, so as to obtain the fluctuation variation of the slab type on the cold-rolled sheet strip, thereby obtaining the slab type defect parameter of the cold-rolled sheet strip and each component related to the slab type defect parameter, and finally, the operation parameter of the cold-rolled sheet rolling mill can be obtained and adjusted according to the slab type defect parameter and each component related to the slab type defect parameter, thereby controlling the slab type of the cold-rolled sheet, avoiding the occurrence of the strip breakage of the cold-rolled sheet, and further improving the yield of the cold-rolled sheet.

Illustratively, as shown in fig. 1, the cold-rolling sheet mill includes a carriage 7, a nut 8, a lead screw 9, a motor 10, a coupling 11, a slide rail 12, and a base 13. Specifically, the bed 1 is installed on a base 13, a motor 10 is installed at one end of the bed 1, a lead screw 9 is connected with the motor 10 through a coupling 11, the lead screw 9 is connected with a sliding frame 7 through a nut 8, and a slide rail 13 is arranged below the sliding frame 7. The working process of the cold-rolled sheet rolling mill is similar to that of the existing cold-rolled sheet rolling mill, and a person skilled in the art can refer to the working process of the existing cold-rolled sheet rolling mill, and the embodiment of the invention is not described again.

Alternatively, as shown in fig. 2, the hydraulic tailstock 3 may include a vertical hydraulic column 31, a horizontal hydraulic column 32, a skid plate 33, and a pallet 34. Specifically, on the lathe bed 1 of the installation of one end of vertical hydraulic column 31, the other end of vertical hydraulic column 31 is installed slide 33, and the top of slide 33 is installed layer board 34, and horizontal hydraulic column 32 is installed between slide 33 and layer board 34 and is continuous with layer board 34, and the one side that layer board 34 keeps away from horizontal hydraulic column 32 links to each other with push rod 4. Under the combined action of the vertical hydraulic column 31 and the horizontal hydraulic column 32, the push rod 4 can be controlled to move up and down and left and right, so that the target measuring target 5 can move up and down and left and right, the target measuring target 5 can move along with the movement of the roller, the plate shape condition of the cold-rolled plate strip can be observed conveniently, and whether the plate shape defect occurs in the cold-rolled plate strip is judged.

Optionally, the cold-rolled sheet profile detection system may further include a distance measuring sensor (not shown in the figure) mounted on the bed 1, the distance measuring sensor is located on a side of the hydraulic tailstock 3 away from the push rod 4, and a connection line between the center of the target measuring target 5 and the center of the distance measuring sensor is parallel to the bed 1 in the horizontal direction. Through setting up range sensor in one side that push rod 4 was kept away from to hydraulic pressure tailstock 3, can use laser instrument 2 to measure the amount of movement of target measurement target 5, use range sensor to measure the amount of movement of target measurement target 5, obtain the fluctuation change volume of the board type on the cold-rolled sheet strip, thereby according to the fluctuation change volume of the board type on the cold-rolled sheet strip that obtains through laser instrument 2 and the fluctuation change volume of the board type on the cold-rolled sheet strip that obtains through range sensor, obtain the fluctuation change volume of the board type on the cold-rolled sheet strip more accurate and accurate, thereby help controlling the board type of cold-rolled sheet more, further avoid the cold-rolled sheet to appear the condition emergence of disconnected area, further improve the yield of cold-rolled sheet.

Alternatively, the laser 2 may be a focused laser to obtain the amount of profile fluctuation on the cold-rolled sheet strip more accurately.

Optionally, the camera 6 may be a high-definition camera, so as to observe the moving track of the target measurement target more clearly, and to help judge the plate shape of the cold-rolled plate strip.

In addition, above-mentioned cold-rolled sheet board type detecting system still can include the main control system, and main control system and laser instrument and range finding sensor wireless connection can directly pass through the main control system like this, and remote control laser instrument and range finding sensor's measurement has improved cold-rolled sheet board type detecting system's use convenience.

As shown in fig. 3, an embodiment of the present invention further provides a method for detecting a cold-rolled sheet profile, including:

and step S1, detecting by using a cold-rolled sheet strip shape detection system to obtain the strip shape fluctuation quantity on the cold-rolled sheet strip. Specifically, the cold-rolled sheet strip can be detected by using the cold-rolled sheet strip detection system, and the strip profile fluctuation variation on the cold-rolled sheet strip is obtained.

And step S2, obtaining the plate shape defects of the cold-rolled plate strip according to the plate shape fluctuation quantity.

For example, in step S1, the step of obtaining the amount of change in the form fluctuation on the cold-rolled sheet strip by using the cold-rolled sheet form detection system to perform detection may include:

and step S11, obtaining the bow height and the bow distance of the bow on the cold-rolled sheet strip through a laser in the cold-rolled sheet strip shape detection system.

And step S12, obtaining the wave height and the wave distance of the edge waves on the cold-rolled sheet strip through a laser.

And step S13, obtaining the wave height and the wave distance of the medium waves on the cold-rolled sheet strip through a laser.

And step S14, obtaining the plate shape fluctuation variation on the cold-rolled plate strip according to the arch height and the arch distance of the arch, the wave height and the wave distance of the edge waves and the wave height and the wave distance of the middle waves.

The beneficial effects of the cold-rolled sheet profile detection method are the same as those of the cold-rolled sheet profile detection system, and therefore, the description is omitted here.

In addition, as shown in fig. 4, an embodiment of the present invention further provides a method for controlling a cold-rolled sheet profile, including:

step SS1, detecting by using a cold-rolled sheet and plate shape detection method to obtain a plate shape defect parameter S of the cold-rolled sheet and plate shape defect parameter Z of the cold-rolled sheet₁Middle wave component Z₂Sum edge wave component Z₃。

For example, the bow component Z can be determined from the measured bow height and bow distance of the bow on the cold-rolled sheet strip₁Wave height sum of edge waves obtained from measurementsObtaining the wave distance from the edge wave component Z₃And the wave height and the wave distance of the middle wave obtain the middle wave component Z₂。

Step SS2, according to plate type defect parameter S, bow component Z₁Middle wave component Z₂Sum edge wave component Z₃Obtaining a bow component coefficient R₁Middle wave component coefficient R₂Sum edge wave component coefficient R₃Wherein, in the step (A),。

step SS3, according to the bow component coefficient R₁Middle wave component coefficient R₂Sum edge wave component coefficient R₃And adjusting the operating parameters of the cold-rolled sheet rolling mill and controlling the cold-rolled sheet profile.

Illustratively, in step SS3, the coefficient R is determined according to the bow component₁Middle wave component coefficient R₂And the edge wave component coefficient R₃Adjusting the operating parameters of the cold-rolled sheet rolling mill, the specific steps of controlling the cold-rolled sheet profile may include:

step SS31, calculating the bow component coefficient R₁Adjusting the roll inclination of the cold-rolled sheet rolling mill as a roll inclination control correction value;

step SS32, the coefficient R of the middle wave component₂Adjusting the bending roll of the cold-rolled sheet rolling mill as an automatic correction value of the bending roll control;

step SS33, dividing the coefficient R of the edge wave component₃The intermediate roll of the cold-rolling mill is adjusted as an intermediate roll control automatic correction value.

In the cold-rolled sheet profile control method provided by the embodiment of the invention, after the sheet profile defect parameter and each component related to the sheet profile defect parameter of the cold-rolled sheet strip are obtained, the coefficient of each component related to each sheet profile defect parameter can be obtained according to the sheet profile defect parameter and each component related to the sheet profile defect parameter, and then each component coefficient is used as an operation parameter for adjusting the cold-rolled sheet rolling mill, so that the cold-rolled sheet profile is controlled, the occurrence of the strip breakage of the cold-rolled sheet is avoided, and the yield of the cold-rolled sheet is further improved.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

It is to be understood that the present invention is not limited to the embodiment methods, structures, and precise structures shown in the drawings, which have been described above, and that various modifications and changes may be made without departing from the scope thereof. The scope of the invention is limited only by the appended claims.