阅读说明：本技术 用于动量轮的去重系统与动量轮的去重方法 (Weight removal system for momentum wheel and weight removal method for momentum wheel ) 是由 孔翔 郭俊美 刘艳玲 汪云涛 徐春剑 鲍涵钰 于 2020-10-13 设计创作，主要内容包括：本发明公开了一种用于动量轮的去重系统与动量轮的去重方法,去重系统包括动平衡机和激光去重装置,动平衡机包括本体和设置于本体的安装座,安装座用于动量轮的安装,本体用于测量动量轮的不平衡量；激光去重装置具有激光头,激光头能够向安装于安装座上的动量轮发射激光,以对动量轮不平衡量进行去重。动量轮通过安装座安装于本体上,动量轮的轮体转动过程中,本体测量出动量轮轮体不平衡量的位置,此时,控制动量轮旋转一定角度,不平衡量被旋转至朝向激光头的位置,激光头向不平衡量发射激光,从而快速、便捷地对动量轮的轮体进行精确去重。(The invention discloses a weight removing system for a momentum wheel and a weight removing method for the momentum wheel, wherein the weight removing system comprises a dynamic balancing machine and a laser weight removing device, the dynamic balancing machine comprises a body and a mounting seat arranged on the body, the mounting seat is used for mounting the momentum wheel, and the body is used for measuring the unbalance amount of the momentum wheel; the laser weight removing device is provided with a laser head, and the laser head can emit laser to the momentum wheel arranged on the mounting seat so as to remove the weight of the unbalance of the momentum wheel. The momentum wheel is installed on the body through the mount pad, and the wheel body of momentum wheel rotates the in-process, and the body measures the position of momentum wheel body unbalance amount, and at this moment, the rotatory certain angle of control momentum wheel, unbalance amount are rotatory to the position towards the laser head, and the laser head is to unbalance amount transmission laser to carry out the accuracy to the wheel body of momentum wheel fast, conveniently and heavily.)

1. A deduplication system for a momentum wheel, comprising:

the dynamic balancing machine comprises a body and a mounting seat arranged on the body, wherein the mounting seat is used for mounting the momentum wheel, and the body is used for measuring the unbalance amount of the momentum wheel;

laser device that weighs, laser device that weighs has the laser head, the laser head can to install in momentum wheel emission laser on the mount pad, in order to right the unbalance amount of momentum wheel carries out the weight.

2. The deduplication system for a momentum wheel of claim 1, further comprising:

a vacuum cabinet defining a vacuum chamber, the body being mounted within the vacuum chamber;

the air extracting device is communicated with the vacuum cavity and is used for enabling the vacuum cavity to be in a vacuum state;

wherein the laser head is located inside the vacuum chamber; or, the laser head is located the outside of vacuum cavity, the vacuum cabinet has transparent portion, transparent portion can supply the laser to pass through.

3. The deduplication system for a momentum wheel according to claim 2,

the transparent part is made of quartz.

4. The system of claim 2, wherein the air extractor is connected to an air extraction duct in communication with the vacuum cabinet.

5. The system of claim 2, wherein the vacuum cabinet has a sealing cover for closing or opening the vacuum chamber, the transparent portion being disposed at the sealing cover.

6. The system of claim 5, wherein the top of the vacuum chamber is provided with an annular receiving groove along the edge thereof, and the sealing groove is embedded with a sealing gasket and can abut against the inner side of the sealing cover.

7. The system of claim 5, wherein the laser de-weighting device comprises:

the laser head is one end of the light source piece;

the light source piece is arranged on the machine cabinet in a sliding mode;

and the adjusting assembly is arranged on the machine cabinet and used for adjusting the light source part to move away from or close to the transparent part.

8. The system of claim 2, wherein the rotor of the momentum wheel has an encoder, and wherein a controller of the encoder is disposed outside the vacuum chamber.

9. A method for removing the weight of a momentum wheel is characterized by comprising the following steps:

measuring an unbalance amount of the momentum wheel;

and emitting laser to the position of the unbalance of the momentum wheel so as to remove the weight of the unbalance of the momentum wheel.

10. A method of momentum wheel de-weighting according to claim 9, wherein the step of measuring the amount of unbalance is performed in a vacuum environment and/or the step of momentum wheel de-weighting is performed in a vacuum environment.

Technical Field

The invention relates to the technical field of satellites, in particular to a weight removing system for a momentum wheel and a weight removing method for the momentum wheel.

Background

The momentum wheel is used as an executive component of an attitude control system of a spacecraft (such as a satellite), and the momentum wheel used for aerospace needs to be balanced with high precision, so that after the momentum wheel is manufactured, the balance of the momentum wheel needs to be measured, and after the momentum wheel is measured, the unbalance of the momentum wheel needs to be weighted or deduplicated.

In the related art, in the process of removing the weight of the momentum wheel, a balance instrument detects the position of the unbalance amount of the momentum wheel, and the excess weight is removed through manual operation (a file or a drilling machine), however, the above method has the problems of slow speed and low precision of removing the weight of the momentum wheel.

Disclosure of Invention

The present invention is directed to solving at least one of the problems of the prior art. Therefore, the invention provides a weight removing system for the momentum wheel, which can quickly and conveniently accurately remove the unbalance of the momentum wheel.

The invention also provides a weight removing method of the momentum wheel.

A deduplication system for a momentum wheel according to an embodiment of a first aspect of the present invention comprises:

the dynamic balancing machine comprises a body and a mounting seat arranged on the body, wherein the mounting seat is used for mounting the momentum wheel, and the body is used for measuring the unbalance amount of the momentum wheel;

laser device that weighs, laser device that weighs has the laser head, the laser head can to install in momentum wheel emission laser on the mount pad, in order to right the unbalance amount of momentum wheel carries out the weight.

The deduplication system for the momentum wheel according to the embodiment of the first aspect of the present invention has at least the following technical effects: the momentum wheel is installed on the body through the mount pad, and the wheel body of momentum wheel rotates the in-process, and the body measures the position of momentum wheel body unbalance amount, and at this moment, the unbalance amount aligns with the laser head, and the laser head is to unbalance amount transmission laser to carry out the accuracy to the wheel body of momentum wheel fast, conveniently and heavily.

According to some embodiments of the invention, further comprising: a vacuum cabinet defining a vacuum chamber, the body being mounted within the vacuum chamber; the air extracting device is communicated with the vacuum cavity and is used for enabling the vacuum cavity to be in a vacuum state; wherein the laser head is positioned inside the vacuum chamber; or, the laser head is located the outside of vacuum cavity, the vacuum cabinet has transparent portion, transparent portion can supply the laser to pass through.

According to some embodiments of the invention, the transparent part is made of quartz.

According to some embodiments of the invention, the air extraction device is connected to an air extraction duct communicating with the vacuum cabinet. .

According to some embodiments of the present invention, the vacuum cabinet has a sealing cover for closing or opening the vacuum chamber, and the transparent part is provided to the sealing cover.

According to some embodiments of the invention, the top of the vacuum cabinet is provided with an annular accommodating groove along the edge thereof, and the sealing groove is embedded with a sealing gasket and can abut against the inner side of the sealing cover.

According to some embodiments of the invention, the laser de-weighting apparatus comprises: the laser head is one end of the light source piece; the light source piece is arranged on the machine cabinet in a sliding mode; and the adjusting and adjusting assembly is arranged on the machine cabinet and is used for adjusting the light source part to move away from or close to the transparent part.

According to some embodiments of the invention, the rotor of the momentum wheel has an encoder, the controller of which is arranged outside the vacuum chamber.

According to the second aspect of the invention, the method for removing the weight of the momentum wheel comprises the following steps: measuring an unbalance amount of the momentum wheel; and emitting laser to the position of the unbalance of the momentum wheel so as to remove the weight of the unbalance of the momentum wheel.

The deduplication system for the momentum wheel according to the embodiment of the second aspect of the present invention has at least the following technical effects: by adopting the method, after the unbalance of the momentum wheel is measured, the laser is emitted to the position of the unbalance of the momentum wheel, so that the momentum wheel is accurately removed.

According to some embodiments of the invention, the step of measuring the amount of unbalance is performed in a vacuum environment and/or the step of de-weighting the momentum wheel is performed in a vacuum environment.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a schematic diagram of a relationship structure of a dynamic balancing machine and a laser de-weighting device according to the present invention;

FIG. 2 is a schematic diagram of the overall structure of the deduplication system of the present invention;

FIG. 3 is a schematic diagram of an exploded structure of the vacuum cabinet of the present invention;

fig. 4 is a vertical sectional view of the sealing cap of the present invention.

Reference numerals:

dynamic balancing machine 100, body 110 and mounting base 120

The device comprises a laser de-weighting device 200, a cabinet 210, a light source part 220 and a laser head 221;

the vacuum cabinet 300, the cabinet body 310, the vacuum cavity 311, the placing opening 312, the flange 313, the containing groove 314, the sealing cover 320, the sealing gasket 330, the transparent part 340, the pressure gauge 350 and the gas spring 360;

the air extracting device 400, the frame 410, the air pump 420 and the air extracting pipeline 430;

the momentum wheel 500.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

A deduplication system for a momentum wheel according to an embodiment of the present invention is described below with reference to fig. 1 and 4.

Referring to fig. 1, the deduplication system for a momentum wheel according to an embodiment of the first aspect of the present invention includes a dynamic balancer 100 and a laser deduplication device 200, where the dynamic balancer 100 includes a body 110 and a mounting base 120, and a momentum wheel 500 is mounted on the mounting base 120, where the body 110 is capable of measuring the position of the unbalance amount of the wheel body of the momentum wheel 500; meanwhile, the laser de-weighting device 200 is located at one side of the dynamic balancing machine 100, and the laser head 221 of the laser de-weighting device 200 can emit laser to the momentum wheel installed on the mounting seat to de-weight the unbalance amount of the momentum wheel.

Specifically, the momentum wheel 500 is mounted on the dynamic balancing machine 100 through the mounting seat 120, and the body 110 measures the position of the unbalance amount of the momentum wheel 500; after the unbalance amount detection is completed, the laser head 221 of the laser de-weighting device 200 emits laser to the wheel body of the momentum wheel 500, and the laser performs accurate de-weighting on the unbalance amount of the wheel body of the momentum wheel 500, so that the momentum wheel 500 required by the satellite is obtained.

Furthermore, after the unbalance amount of the momentum wheel 500 is detected, the momentum wheel 500 is controlled to rotate a certain angle by using the characteristics (common knowledge in the art) of the momentum wheel 500, the unbalance amount is rotated to face the laser head 221, and the laser head 221 performs the de-weighting of the momentum wheel 500 quickly and conveniently.

In some embodiments, referring to fig. 2 and 3, the laser de-weighting apparatus 200 further comprises a vacuum cabinet 300 and a gas-pumping device 400, the vacuum cabinet 300 is vertically disposed, the inner side of the vacuum cabinet 300 defines a vacuum chamber 311, the dynamic balancing machine 100 is vertically mounted in the vacuum chamber 311, and thus, the momentum wheel 500 is inspected in the vacuum chamber 311; meanwhile, the evacuation device 400 is installed outside the vacuum chamber 300, an evacuation line 430 is connected between the evacuation device 400 and the vacuum chamber 300, the evacuation device 400 is connected to the vacuum chamber 311 through the evacuation line 430, and the gas in the vacuum chamber 311 is evacuated through the evacuation line 430, so that the vacuum chamber 311 is in a vacuum state.

Specifically, when the momentum wheel 500 is detected, the air extractor 400 extracts air in the vacuum cavity 311, the vacuum cavity 311 is in a vacuum state, at this time, the wheel body of the momentum wheel 500 rotates in the vacuum state, the wheel body of the momentum wheel 500 does not receive external wind resistance, and the dynamic balancing machine 100 can accurately measure the position of the unbalance amount of the momentum wheel 500; in addition, in the measuring process of the momentum wheel 500, the laser de-weighting device 200 precisely removes the unbalance of the momentum wheel 500 by using laser, and the momentum wheel 500 gradually balances, so as to obtain the momentum wheel 500 required by the satellite. In summary, the weight removing system of the present embodiment has two functions of accurately measuring the unbalance amount of the momentum wheel 500 and accurately removing the weight, that is, when the balance amount of the momentum wheel 500 is measured, the weight removing of the momentum wheel 500 is simultaneously achieved.

In some embodiments, a pressure release valve is disposed on the front surface of the vacuum cabinet 300 for restoring the vacuum chamber 311 to a normal pressure, and in particular, after the weight removal by the momentum wheel 500 is completed, the pressure release valve on the upper portion of the front surface of the vacuum cabinet 300 is opened to allow the gas outside the vacuum cabinet 300 to enter the vacuum cabinet 300, so that the vacuum cabinet 300 is restored to the normal pressure, thereby facilitating the opening of the sealing cover 320 of the vacuum cabinet 300.

It is understood that the laser de-weighting apparatus 200 may be mounted within the vacuum cavity 311 with the laser head 221 of the laser de-weighting apparatus 200 facing the circumferential surface of the momentum wheel 500 body; therefore, during the detection process of the momentum wheel 500, the laser head 221 of the laser de-weighting device 200 performs de-weighting by aligning the position of the unbalance amount of the momentum wheel 500.

Also, the laser de-weighting apparatus 200 may be mounted outside the vacuum chamber 311. The vacuum cabinet 300 has a transparent part 340, and the transparent part 340 is aligned with the circumferential surface of the wheel body of the momentum wheel 500; meanwhile, the laser head 221 of the laser de-weighting device 200 is disposed outside the vacuum chamber 311, and the laser generated by the laser head 221 passes through the transparent part 340, thereby de-weighting the wheel body of the momentum wheel 500.

It will be appreciated that by locating the momentum wheel 500 outside the vacuum chamber 311, the position of the laser de-weighting device 200 may be easily adjusted depending on the body of the momentum wheel 500.

In some embodiments, the transparent part 340 is made of quartz, and the laser light passing through the transparent part 340 does not damage the transparent part 340, thereby ensuring the sealing performance of the vacuum chamber 311 and the accurate removal of the unbalance of the wheel body of the momentum wheel 500.

It should be noted that, the sidewall of the vacuum cabinet 300 is provided with a mounting hole, a lead electrically connected with the dynamic balancing machine 100 and a lead electrically connected with the momentum wheel 500 are electrically connected with a socket, and the socket is hermetically connected in the mounting hole; meanwhile, the wires of the electrical components outside the vacuum cabinet 300 are connected with plugs, and the plugs are plugged into the sockets, so that the momentum wheel 500 and the dynamic balancer 100 are electrically connected with the external electrical components.

In some embodiments, the vacuum chamber 300 includes a cabinet 310 and the sealing cover 320, the vacuum chamber 311 is a cavity inside the cabinet 310, the dynamic balancing machine 100 is installed inside the cabinet 310, the top of the cabinet 310 has a placing opening 312, and the placing opening 312 is used for installing or removing the momentum wheel 500. Meanwhile, the edge of the sealing cover 320 is provided with a rotating part which is vertically and rotatably connected to the outside of the edge of the placing opening 312 through a hinge and is switched between a first position and a second position, when the sealing cover 320 is at the first position, the sealing cover 320 is just buckled at the placing opening 312, so that the placing opening 312 is sealed; when the sealing cover 320 is in the second position, the sealing cover 320 just opens the placing opening 312, which facilitates the removal or placement of the momentum wheel 500.

The transparent part 340 is a glass plate formed by a quartz support, the central part of the sealing cover 320 is provided with a square mounting opening, and the transparent part 340 is horizontally arranged in the mounting opening and is connected with the inner wall of the mounting opening in a sealing way; since the laser de-weighting device 200 is disposed outside the vacuum cabinet 300, the laser head 221 of the laser de-weighting system is located right above the transparent portion 340, the laser head 221 faces the transparent portion 340 vertically, that is, the laser vertically penetrates through the transparent portion 340 and irradiates on the wheel body of the momentum wheel 500, and the unbalance amount of the wheel body of the momentum wheel 500 is accurately removed.

In a further embodiment, the sealing cover 320 can be further ensured to be capable of tightly sealing the vacuum cavity 311, the top of the cabinet body 310 is provided with a flange 313 which is horizontally folded outwards, the top of the flange 313 is provided with an annular edge which is positioned around the placing opening 312, the annular edge is provided with an annular accommodating groove 314, a sealing gasket 330 made of flexible rubber is embedded in the accommodating groove 314, and the sealing gasket 330 is positioned outside the accommodating groove 314; when the sealing cover 320 is engaged with the upper side of the flange 313, the sealing gasket 330 is deformed accordingly and abuts against the inner side of the sealing cover 300, thereby sealing the gap between the sealing cover 320 and the flange 313 tightly and keeping the vacuum chamber 311 in a vacuum state.

In some embodiments, the sealing cover 320 is further fastened to the flange 313, and a plurality of fasteners are uniformly distributed around the flange 321, wherein the fasteners include a screw rod vertically and rotatably connected to the flange, and a locking member abutting against the upper surface of the sealing cover 320 is threadedly connected to the screw rod.

In some embodiments, the sealing cover 320 is further conveniently opened, the gas spring 360 is arranged between the sealing cover 320 and the cabinet body 310, specifically, the first mounting seat is fixedly arranged on the base of the cabinet body 310, the second mounting seat is fixedly arranged on the sealing cover, the gas spring 360 is connected between the first mounting seat and the second mounting seat, the lower end of the gas spring 360 is vertically and rotatably connected to the first mounting seat, and the upper end of the gas spring 360 is vertically and rotatably connected to the second mounting seat, so that when the sealing cover 320 is opened, the gas spring 360 gradually extends, the sealing cover 320 can be pushed to rotate upwards, and the sealing cover 320 is further conveniently opened.

In some embodiments, a pressure gauge 350 is disposed on an upper portion of a sidewall of the cabinet 310, and the indication of the pressure gauge 350 is used to determine a vacuum condition in the vacuum chamber 311, and an unbalance amount of the wheel body of the momentum wheel 500 is detected when the vacuum condition of the vacuum chamber 311 reaches a standard.

In some embodiments, the laser de-weighting device 200 includes a cabinet 210 and a light source 220, the cabinet 210 is vertically disposed and separated from the vacuum cabinet 300, the light source 220 is horizontally disposed on the cabinet 210, the laser head 221 is an end of the light source 220 and vertically faces the transparent portion 340, so that the laser passes through the transparent portion 340 and irradiates on the wheel body of the momentum wheel 500, and the wheel body of the momentum wheel 500 is precisely de-weighted.

Further, the light source unit 220 is vertically slidably connected to the cabinet 210, and an adjusting assembly (not shown) is disposed on the cabinet 210, and the adjusting assembly adjusts the light source unit 220 to vertically slide, that is, the laser head 221 moves away from or close to the sealing cover 320. When the wheel body of the momentum wheel 500 is removed, the adjusting assembly adjusts the light source part 220 to slide vertically according to the condition of the momentum wheel 500, and the laser head 221 is adjusted to an adaptive position, so that the wheel body of the momentum wheel 500 is accurately removed; meanwhile, when it is required to open the vacuum chamber 311, the sealing cover 320 is rotated upward and opened, thereby mounting the momentum wheel 500 on the mount 120 of the dynamic balancer 100 or taking out the momentum wheel 500 on the dynamic balancer 100; however, since the laser head 221 is closer to the sealing cover 320, the adjusting component adjusts the light source part 220 to move away from the sealing cover 320, so that when the light sealing cover 320 is opened, the sealing cover 320 is prevented from touching the light source part 220, and further subsequent use of the light source part 220 is prevented from being affected.

In a further embodiment, the adjusting assembly includes a stepping motor, a screw rod, and a sliding seat (not shown in the figure), the screw rod is vertically disposed in the cabinet 210 and rotatably connected to the cabinet 210, the sliding seat is vertically slidably connected to the cabinet 210, a portion of the sliding seat is screwed to the screw rod, the light source element 220 is fixedly mounted to another portion of the sliding seat, and a driving shaft of the stepping motor is fixedly connected to one end of the screw rod through a coupling. Specifically, the stepping motor drives the screw to rotate, and the sliding seat is in threaded connection with the screw, so that the sliding seat vertically slides to drive the light source piece 220 to vertically slide.

In addition, the stepping motor may be a rotation knob, and the user rotates the lead screw by rotating the knob, thereby adjusting the light source unit 220.

In some embodiments, an encoder (not shown) is disposed on the rotor of the momentum wheel 500, a controller of the encoder is located outside the vacuum chamber 300, the encoder is controlled by the controller, the encoder controls the rotor to precisely rotate the momentum wheel 500 within a certain angle, so that the unbalance amount of the wheel body of the momentum wheel 500 rotates upwards to an upward state, and the laser generated by the laser head 221 passes through the transparent part 340 and precisely removes the unbalance amount.

In some embodiments, the air-extracting apparatus 400 includes a frame 410 and an air pump 420, wherein the frame 410 is disposed vertically, the air pump 420 is mounted on the frame 410, and an end of the air-extracting duct 430 away from the vacuum chamber 300 is connected to the air pump 420, so as to perform air-extracting and air-discharging of the vacuum chamber 311.

It will be appreciated that the gas evacuation device 400, vacuum cabinet 300 and laser de-weighting device 200 are provided separately and independently, thereby facilitating maintenance or replacement of the gas evacuation device 400, vacuum cabinet 300 and laser de-weighting device 200, respectively.

The method for removing the weight of the momentum wheel according to the embodiment of the second aspect of the invention specifically comprises the following steps:

step 1, measuring the unbalance amount of the momentum wheel 500 in a vacuum environment.

And 2, emitting laser to the position of the unbalance of the momentum wheel 500 in a vacuum environment to remove the unbalance of the momentum wheel 500.

Specifically, the momentum wheel 500 is mounted on the dynamic balancing machine 100, that is, the momentum wheel 500 is mounted on the mounting seat 120 of the body 110 and the sealing cover 320 is closed, and the momentum wheel 500 is enclosed in the vacuum chamber 311. The air pump 420 is activated, and the air pump 420 pumps air out of the vacuum chamber 311 through the air pumping line 430, so that the vacuum chamber 311 is a vacuum environment, thereby providing a vacuum environment for the measurement of the unbalance amount of the momentum wheel 500. The dynamic balancer 100 is started, and the unbalance amount of the dynamic balancer 100 is accurately measured in a vacuum environment in the rotating process of the wheel body of the momentum wheel 500. After the unbalance amount is measured, the controller controls the rotor of the momentum wheel 500 to rotate through the encoder, the wheel body of the momentum wheel 500 is rotated, the unbalance amount on the wheel body of the momentum wheel 500 is adjusted to face the laser head 221, at the moment, the light source part 220 is started, the light source part 220 emits laser to the unbalance amount through the laser head 221, the laser penetrates through the transparent part 340 and further irradiates on the wheel body of the momentum wheel 500, the unbalance amount of the momentum wheel 500 is removed, and the momentum wheel 500 required by a satellite is obtained.

It can be understood that, the dynamic balancing machine 100 measures the unbalance amount of the momentum wheel 500 in a vacuum environment, and the momentum wheel 500 does not receive external wind resistance, so as to accurately measure the unbalance amount; in addition, the dynamic balancing machine 100 performs the weight removal of the momentum wheel 500 body in the vacuum environment, the weight removal of the momentum wheel 500 is convenient, and the weight removal efficiency of the momentum wheel 500 body is improved.

In the description of the present specification, reference to the description of the terms "one embodiment," "some embodiments," "an illustrative embodiment," "an example," "a specific example," or "some examples" or the like means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

While embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.