阅读说明：本技术 一种空调压缩机装配线及控制方法 (air conditioner compressor assembly line and control method ) 是由 兰江华 于 2019-09-19 设计创作，主要内容包括：本发明提供了一种空调压缩机装配线及控制方法,空调压缩机装配线包括：第一输送段和第二输送段,第一输送段连续配置在第二输送段输送方向的下游,第二输送段与第一输送段的输送方向相同；第二输送段用于将压缩机装配到空调外机的底盘上,第一输送段用于将压缩机的泵脚螺栓和螺母锁紧；第二输送段包括第二传送链和第二控制箱,第二控制箱用于控制第二传送链的传送速度；第一输送段包括第一传送链和第一控制箱,第一控制箱用于控制第一传送链的传送速度。本发明空调压缩机装配线的两个输送段的传送速度可独立控制,能够通过调整传送速度避免前后工件碰撞,从而杜绝泵脚螺栓歪斜的情况发生,减少空调外机产生的噪音。(The invention provides an air conditioner compressor assembly line and a control method, wherein the air conditioner compressor assembly line comprises: the conveying device comprises a first conveying section and a second conveying section, wherein the first conveying section is continuously arranged at the downstream of the conveying direction of the second conveying section, and the conveying direction of the second conveying section is the same as that of the first conveying section; the second conveying section is used for assembling the compressor to a chassis of an air conditioner external unit, and the first conveying section is used for locking a pump foot bolt and a nut of the compressor; the second conveying section comprises a second conveying chain and a second control box, and the second control box is used for controlling the conveying speed of the second conveying chain; the first conveying section comprises a first conveying chain and a first control box, and the first control box is used for controlling the conveying speed of the first conveying chain. The conveying speeds of the two conveying sections of the assembly line of the air conditioner compressor can be independently controlled, and front and rear workpieces can be prevented from colliding by adjusting the conveying speeds, so that the condition that a pump leg bolt is inclined is avoided, and noise generated by an air conditioner external unit is reduced.)

1. an air condition compressor assembly line, its characterized in that includes:

a first conveying section (100) and a second conveying section (200), the first conveying section (100) being arranged continuously downstream in the conveying direction of the second conveying section (200), the conveying direction of the second conveying section (200) being the same as the conveying direction of the first conveying section (100);

The second conveying section (200) is used for assembling the compressor to a chassis of an air conditioner external unit, and the first conveying section (100) is used for locking a pump leg bolt and a nut of the compressor;

the second conveying section (200) comprises a second conveying chain (6) and a second control box (7), and the second control box (7) is used for controlling the conveying speed of the second conveying chain (6);

The first conveying section (100) comprises a first conveying chain (1) and a first control box (2), wherein the first control box (2) is used for controlling the conveying speed of the first conveying chain (1).

2. the air conditioner compressor assembly line of claim 1,

the second conveying section (200) further comprises a second speed detection device, the workpieces positioned on the second conveying section (200) are second workpieces, the second speed detection device is used for detecting the actual conveying speed of the second workpieces, and the second control box (7) is further used for controlling the conveying speed of the second conveying chain (6) according to the detection result of the second speed detection device;

the first conveying section (100) further comprises a first speed detection device, the workpiece positioned on the first conveying section (100) is a first workpiece, the first speed detection device is used for detecting the actual conveying speed of the first workpiece, and the first control box (2) is further used for controlling the conveying speed of the first conveying chain (1) according to the detection result of the first speed detection device.

3. the air conditioner compressor assembly line of claim 2,

The second conveying section (200) further comprises a stop control device which controls the second conveying chain (6) to stop when the detection result of the first speed detection device meets a stop condition.

4. the air conditioner compressor assembly line of claim 1,

The first conveying section (100) further comprises a first emergency stop switch (5) for controlling the first transmission chain (1) and the second transmission chain (6) to stop synchronously;

the second conveying section (200) further comprises a second emergency stop switch (10) for controlling the second conveying chain (6) to stop.

5. a control method of an assembly line of an air conditioner compressor is characterized in that,

for controlling an air conditioning compressor assembly line as claimed in any one of claims 1 to 4,

the control method comprises the following steps:

and controlling a second conveying speed of the second conveying chain to be Vg, controlling a first conveying speed of the first conveying chain to be Vb, and enabling the first conveying speed and the second conveying speed to meet the relation that Vb is less than or equal to Vg.

6. The control method of an assembly line of an air conditioner compressor as claimed in claim 5,

the first conveying speed Vb is (0.07-0.12) m/s.

7. The control method of an assembly line of an air conditioner compressor as claimed in claim 5,

The workpiece positioned on the second conveying section (200) is a second workpiece, and the workpiece positioned on the first conveying section (100) is a first workpiece;

the control method further comprises the following steps:

When the first actual conveying speed of the first workpiece is different from the first conveying speed, controlling the first actual conveying speed of the first workpiece to be V1, controlling the second actual conveying speed of the second workpiece to be V2, and meeting the relation V2-V1 (0.8-1.1).

8. The control method of an assembly line of an air conditioner compressor as claimed in claim 7,

The control method further comprises the following steps:

And when the first actual conveying speed and the first conveying speed meet V1 ≤ x Vb, controlling the second conveying chain (6) to stop by a stop control device, wherein x is a stop coefficient.

9. The control method of an assembly line of an air conditioner compressor as claimed in claim 8,

The shutdown coefficient x satisfies the following formula:

in the formula (I), the compound is shown in the specification,

x represents the stop coefficient and the stop coefficient,

The deformation amount of the bolt of the pump foot is shown,

k2 represents the pump foot bolt impact deformation coefficient,

vb denotes a first conveying speed of the first conveyor chain,

V2 represents a second actual conveyance speed of workpiece No. two,

V1 represents the first actual conveyance speed of workpiece number one.

10. The control method of the assembly line of the air conditioner compressor as claimed in claim 9, wherein the shutdown coefficient x is 0.8.

Technical Field

the invention relates to the technical field of air conditioners, in particular to an assembly line of an air conditioner compressor and a control method.

background

Along with the popularization of air conditioners, consumers attach more and more importance to the use experience of products and do not meet the realization of a simple heat exchange function any more, and the operation noise of the air conditioner is an important index influencing the user experience, so that the problem of solving various noise-generating sources is particularly critical in order to improve the quality of the air conditioner.

investigation finds that the deflection of the pump foot bolt of the compressor in the prior art is an important factor causing the resonance noise of the external machine to be large, and the noise is obviously reduced after the pump foot bolt is straightened. The reason for causing the inclination of the bolt of the pump foot of the compressor is as follows: the air conditioner compressor assembly line comprises two continuous processes of a compressor positioning section and a bolt locking section, wherein the compressor positioning section is arranged in front of the bolt locking section, the compressor is assembled on a chassis of an air conditioner outer unit in the compressor positioning section, and a pump foot bolt and a nut of the compressor are locked in the bolt locking section. The assembly line runs continuously, the distance between adjacent workpieces is small, when the conveying speed of the chassis on the bolt locking section is lower than that of the chassis on the compressor positioning section, the rear workpiece can collide with the front workpiece, and thus the compressor on the rear chassis can topple, so that the pump foot bolt of the compressor is pulled askew. And the workman of bolt locking section process only can right the compressor of empting, can not follow the condition of pump foot bolt, leads to the pump foot bolt of product crooked, and crooked bolt can block the hole on chassis, makes the compressor vibration pass through the pump foot bolt and transmits to the machine, arouses resonance, and then produces the noise, influences user experience.

disclosure of Invention

the invention solves the problem that the noise of an air conditioner external unit is overlarge due to the fact that a pump leg bolt is inclined in the assembling process of a compressor.

in order to solve the above problems, the present invention provides an assembly line for an air conditioner compressor, comprising:

A first conveying section and a second conveying section, the first conveying section being continuously disposed downstream in a conveying direction of the second conveying section, the second conveying section being in the same conveying direction as the first conveying section;

The second conveying section is used for assembling the compressor to a chassis of an air conditioner external unit, and the first conveying section is used for locking a pump foot bolt and a nut of the compressor;

the second conveying section comprises a second conveying chain and a second control box, and the second control box is used for controlling the conveying speed of the second conveying chain;

the first conveying section comprises a first conveying chain and a first control box, and the first control box is used for controlling the conveying speed of the first conveying chain.

Compared with the prior art, the conveying speeds of the two conveying sections of the assembly line of the air conditioner compressor can be independently controlled, and the collision of front and rear workpieces can be avoided by adjusting the conveying speeds, so that the situation that a pump leg bolt is inclined is avoided, and the noise generated by an air conditioner external unit is reduced.

Optionally, the second conveying section further includes a second speed detection device, the workpiece located on the second conveying section is a second workpiece, the second speed detection device is configured to detect an actual conveying speed of the second workpiece, and the second control box is further configured to control a conveying speed of the second conveying chain according to a detection result of the second speed detection device; the first conveying section further comprises a first speed detection device, the workpiece positioned on the first conveying section is a first workpiece, the first speed detection device is used for detecting the actual conveying speed of the first workpiece, and the first control box is further used for controlling the conveying speed of the first conveying chain according to the detection result of the first speed detection device.

When the workman was artifical when stirring the work piece, the transfer rate of work piece is different with the transfer rate of transfer chain, sets up the actual transfer rate that speed detection device can detect the work piece at the transport section, and then control transfer rate prevents that the work piece from colliding, avoids the compressor to empty and make pump foot bolt crooked.

Optionally, the second conveying section further includes a stop control device that controls the second conveyor chain to stop when the detection result of the first speed detection device satisfies a stop condition.

when the actual conveying speed of the first workpiece is too low, the second workpiece may collide with the first workpiece to cause the compressor to topple, so that a stop control device needs to be arranged to stop the second conveying chain in time, the collision of the front workpiece and the rear workpiece is avoided, and the stable conveying of the workpieces is further guaranteed.

Optionally, the first conveying section comprises a first emergency stop switch for controlling the first transmission chain and the second transmission chain to stop synchronously; the second conveying section comprises a second emergency stop switch for controlling the second conveying chain to stop.

set up emergency stop switch and can promptly be shut down when the operating mode is unusual, and first emergency stop switch can be shut down two transport sections in step, and the second is carried the section and is continued the operation when preventing first transport section abnormal conditions from shutting down, and No. two work pieces catch up a work piece and collide, and second emergency stop switch only can make the second carry the section and shut down, can not influence first transport section operation, guarantees the independence of second transport section operation when emergency.

the invention also discloses a control method of the air conditioner compressor assembly line, which is used for controlling the air conditioner compressor assembly line and comprises the following steps:

And controlling a second conveying speed of the second conveying chain to be Vg, controlling a first conveying speed of the first conveying chain to be Vb, and enabling the first conveying speed and the second conveying speed to meet the relation that Vb is less than or equal to Vg.

The first conveying speed is controlled to be equal to or less than the second conveying speed, the second workpiece cannot catch up with the first workpiece, and the phenomenon that the compressor is toppled due to collision of the front workpiece and the rear workpiece is avoided, so that the situation that a pump leg bolt is inclined is avoided, and noise generated by an air conditioner external unit is reduced.

optionally, the first conveying speed Vb is (0.07-0.12) m/s. The assembly production rate of the compressor is ensured.

Optionally, the workpiece on the second conveying section is a second workpiece, and the workpiece on the first conveying section is a first workpiece;

the control method further comprises the following steps:

when the first actual conveying speed of the first workpiece is different from the first conveying speed, the first actual conveying speed of the first workpiece is controlled to be V1, the second actual conveying speed of the second workpiece is controlled to be V2, and the first actual conveying speed and the second actual conveying speed meet the relation V2-V1 (0.8-1.1).

Optionally, the control method further includes:

And when the first actual conveying speed and the first conveying speed meet V1 not more than x Vb, the stop control device controls the second conveying chain to stop, and x is a stop coefficient.

When the difference between the actual conveying speed of the first workpiece and the conveying speed of the first conveying chain is too large, if the impact force generated by the collision of the second workpiece with the first workpiece is large, the deformation of the pump foot after the collision is large, the noise generated by an air conditioner external unit is greatly increased, and therefore when the actual conveying speed of the first workpiece is too low, the second conveying chain needs to be stopped, and the second workpiece is prevented from overtaking the first workpiece to collide.

optionally, the shutdown coefficient x satisfies the following formula:

In the formula (I), the compound is shown in the specification,

x represents the stop coefficient and the stop coefficient,

The deformation amount of the bolt of the pump foot is shown,

k2 represents the pump foot bolt impact deformation coefficient,

vb denotes a first conveying speed of the first conveyor chain,

V2 represents a second actual conveyance speed of workpiece No. two,

v1 represents the first actual conveyance speed of workpiece number one.

The relation between the conveying speed of the workpiece and the skew degree of the bolt of the pump foot is determined by the formula, and the deformation of the pump foot needs to be controlled within 0-0.5 mm, so that the shutdown coefficient can be calculated according to the formula, the phenomenon that the press topples due to the front and back impact of the workpiece, the deformation of the bolt of the pump foot is too large, and serious resonance noise is generated is avoided.

Optionally, the shutdown coefficient x is 0.8. The shutdown coefficient is calculated according to a formula, when V1 is greater than 0.8Vb, the noise of an air conditioner external unit is qualified, so when V1 is less than or equal to 0.8Vb, the second conveying section needs to be forcibly shut down, and a second workpiece is prevented from colliding with a first workpiece.

Drawings

FIG. 1 is a schematic diagram of an assembly line collision state of an air conditioner compressor;

Fig. 2 is a schematic view of an assembly line of an air conditioner compressor in a normal operation state according to an embodiment of the invention.

description of reference numerals:

100-a first conveying section, 200-a second conveying section, 1-a first conveying chain, 2-a first control box, 3-a compressor, 4-a chassis, 5-a first emergency stop switch, 6-a second conveying chain, 7-a second control box, 8-a second compressor, 9-a second chassis, 10-a second emergency stop switch, 11-a pump foot bolt and 12-an infrared switch.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

In the description of the present invention, it should be noted that the terms "first" and "second" mentioned in the embodiments of the present invention are only used for descriptive purposes and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

terms such as "front", "rear", and the like in the embodiments of the present invention indicate terms of orientation, which are used for simplifying the description of the positional relationship based on the drawings of the specification, and do not represent that elements, devices, and the like which are referred to must operate according to the operation and method, configuration specified and defined in the specification, and such terms of orientation do not constitute limitations of the present invention.

Referring to fig. 1 and 2, an embodiment of the invention discloses an assembly line and a control method for an air conditioner compressor. The air conditioner compressor assembly line comprises a first conveying section 100 and a second conveying section 200, the conveying directions of the first conveying section 100 and the second conveying section 200 are the same, the second conveying section 200 is used for assembling a compressor on a base plate of an air conditioner external unit, the first conveying section 100 is used for locking a pump foot bolt and a nut of the compressor, the first conveying section 100 is continuously arranged at the downstream of the second conveying section 200, therefore, the assembly line operation can be realized, the first conveying section 100 enters the second conveying section 200 for fastening immediately after the compressor is positioned and assembled, and the production efficiency is improved.

the first conveying section 100 includes a first conveyor chain 1, a first control box 2, a first emergency stop switch 5, and a first speed detection device. The second conveying section 200 comprises a second conveyor chain 6, a second control box 7, a second emergency stop switch 10 and second speed detection means. In this embodiment, the first conveyor chain 1 is a plate conveyor chain, and the second conveyor chain 6 is a roller conveyor chain. The workpiece located on the first conveying section 100 is a first workpiece, the first compressor 3 and the first chassis 4 in fig. 1 and 2 form the first workpiece, the workpiece located on the second conveying section 200 is a second workpiece, and the second compressor 8 and the second chassis 9 form the second workpiece. The first control box 2 is used for controlling the conveying speed of the first conveying chain 1, the first emergency stop switch 5 is used for synchronously controlling the first conveying chain 1 and the second conveying chain 6 to stop, and the second conveying section 200 is prevented from continuously running when the first conveying section 100 stops in abnormal conditions, and a second workpiece catches up with a first workpiece to collide. The second control box 7 is used for controlling the conveying speed of the second conveying chain 6, the second emergency stop switch 10 is used for independently controlling the second conveying chain 6 to stop, the operation of the first conveying section 100 cannot be influenced, and the independence of the operation of the second conveying section 200 in an emergency situation is ensured when the compressor and the chassis which are assembled in the first conveying section 100 are conveyed to the subsequent process.

As shown in fig. 1, when the conveying speed of the first workpiece is slower than that of the second workpiece, the second workpiece can catch up with the first workpiece, the second chassis 9 collides with the first chassis 4, the second compressor 8 tilts forward under the action of inertia, the pump foot bolt 11 of the compressor is bent, the second workpiece is conveyed forward continuously, a worker in the first conveying section 100 can right the compressor and then lock the pump foot bolt 11, and the inclined pump foot bolt 11 is not straightened. The inclined pump foot bolt 11 and the compressor chassis are clamped mutually, so that vibration is transmitted to an outer machine through the bolt when the compressor runs, the outer machine generates resonance noise, and user experience is influenced. The relationship between the skew condition of the pump foot bolt 11 and the resonance noise satisfies the following formula:

In the formula (I), the compound is shown in the specification,

At represents the total noise value (dB (A)) generated by the external unit with the inclined pump leg bolt of the compressor,

A1 represents the total noise value (dB (a)) generated by the external unit with the normal pump foot bolt of the compressor,

k1 represents the coefficient of variation of the noise,

the deformation amount (mm) of the pump foot bolt 11 is shown.

Wherein, the noise variation coefficient k1 is generally between 2.0-4.0, and the noise variation coefficient is related to the weight of the compressor, when the weight of the compressor is less than or equal to 6Kg, k1 is 2.0-2.5; when the weight of the compressor is more than 6Kg and less than or equal to 10Kg, k1 is 2.5-3.0; when the weight of the compressor is more than 10Kg, k1 is 3.0-4.0.

deformation of pump foot boltnoise does not exceed standard when between 0mm ~ 0.5mm, consequently can avoid the front and back work piece collision through adjusting the transfer rate of two transport sections, and then prevent that the compressor from toppling over and making pump foot bolt 11 crooked, reduces the noise that the outer machine of air conditioner produced, promotes user experience.

however, in the actual production and assembly process, the actual conveying speed of the workpiece may be different from the conveying speed of the conveying chain, and in the first conveying section 100, a worker may stir the first workpiece, and the actual conveying speed of the workpiece may be changed, so that only the conveying speeds of the first conveying chain 1 and the second conveying chain 6 are controlled, and the situation that the second workpiece catches up with the first workpiece and collides may still occur. In the present embodiment, the first conveying section 100 is provided with first speed detecting means for detecting an actual conveying speed of the first workpiece, the first control box 2 may control a conveying speed of the first conveying chain 1 based on a detection result of the first speed detecting means, the second conveying section 200 is provided with second speed detecting means for detecting an actual conveying speed of the second workpiece, and the second control box 7 may control a conveying speed of the second conveying chain 6 based on a detection result of the second speed detecting means. The speed detection device can detect the actual conveying speed of the workpiece, and then the operation parameters of the conveying chain are adjusted according to the actual conveying speed, so that the collision of the front workpiece and the rear workpiece is prevented. The first speed detection device and the second speed detection device can be selected from equipment such as an infrared speed measurement device, a radar speed measurement device and an acoustic wave speed measurement device.

In addition, when the difference between the actual conveying speed of the first workpiece and the conveying speed of the first conveying chain 1 is too large, if the impact force generated by the collision of the second workpiece with the first workpiece is large, the deformation of the pump foot after the collision is large, and the noise generated by the air conditioner external unit is too large. Therefore, when the actual conveying speed of the first workpiece is too slow, the second conveying chain 6 needs to be stopped immediately to avoid the collision of the second workpiece with the first workpiece. The present embodiment provides stop control means in the second conveying section 200, and when the detection result of the first speed detecting means satisfies the stop condition, the stop control means controls the second conveying chain 6 to stop. In this embodiment, the stop control device is an infrared switch 12, when the transmission speed of the first transmission chain 1 and the actual transmission speed of the first workpiece satisfy the stop condition, the infrared switch 12 controls the second transmission section 200 to stop, the second transmission chain 6 stops running, and after the actual transmission speed of the first workpiece returns to normal, the infrared switch 12 controls the second transmission chain 6 to start, and the second transmission section 200 returns to normal running. And reasonable shutdown conditions are set, so that the shutdown control device can thoroughly prevent the pump foot bolt 11 from being bent due to the fact that the compressor is toppled.

the control method of the air conditioner compressor assembly line comprises the following processes:

the assembly line starts to run, the workpieces are continuously placed on the conveyor chains, the second control box 7 controls the second conveying speed Vg of the second conveyor chain 6, and the first control box 2 controls the first conveying speed Vb of the first conveyor chain 1. The workpiece is pre-positioned with the chassis and compressor at the second conveyor section 200 and then conveyed downstream to the first conveyor section 100 for nut tightening. The workpiece located on the second conveying section 200 is a second workpiece, and the workpiece located on the first conveying section 100 is a first workpiece.

The first conveying speed Vb is controlled to be (0.07-0.12) m/s, and the first conveying speed and the second conveying speed are controlled to meet the relation that Vb is less than or equal to Vg, so that the second workpiece cannot catch up with the first workpiece, the phenomenon that the compressor is toppled due to front-back collision is avoided, and the situation that the pump foot bolt 11 is inclined is avoided. In order to ensure the production efficiency, the first conveying speed is controlled to be close to the second conveying speed, and the optimal state is Vb ═ Vg, at the moment, the production efficiency is highest.

when a worker carries out a nut locking operation, the first workpiece on the first conveying section 100 may fluctuate, the actual conveying speed of the workpiece needs to be monitored and controlled, the conveying speed of the conveying chain is adjusted according to the detection result of the speed detection device, the first actual conveying speed of the first workpiece is controlled to be V1, the second actual conveying speed of the second workpiece is controlled to be V2, and the first actual conveying speed and the second actual conveying speed meet the relation V2-V1 (0.8-1.1), preferably V2-V1 (0.95-1.05). The second workpiece is ensured not to collide with the first workpiece, and the conveying speed of the second workpiece is not greatly different from that of the first workpiece, otherwise, the production efficiency is influenced.

when the first actual conveying speed V1 is not less than x Vb, the infrared switch 12 controls the second conveying chain 6 to stop, the second conveying section 200 stops, and x is a stop coefficient. The shutdown coefficient x satisfies the following formula:

In the formula (I), the compound is shown in the specification,

x represents the stop coefficient and the stop coefficient,

Indicates the deformation amount (mm) of the pump foot bolt,

k2 represents the pump foot bolt impact deformation coefficient,

vb denotes a first conveying speed (m/s) of the first conveyor chain,

V2 represents a second actual conveyance speed (m/s) of the workpiece No. two,

v1 represents the first actual conveyance speed (m/s) of the workpiece No. one.

equation 2 determines the relationship between the workpiece conveyance speed and the inclination of the pump leg bolt, and equation 1 shows that the deformation amount of the pump leg bolt needs to be controlled to 0mm to 0.5 mm. Therefore, the shutdown coefficient can be calculated according to the formula 2, so that the phenomenon that the press topples due to the front and back impact of the workpiece is avoided, the deformation of the pump foot bolt 11 is too large, and serious resonance noise is generated is avoided.

specifically, the method comprises the following steps:

∵

∴

∴Taking k2 as 2.2 and V2 as 1.1V 1;

∴X＞0.8。

When V1 is more than 0.8Vb, the assembly line of the air conditioner compressor normally runs; when V1 is less than or equal to 0.8Vb, the infrared switch 12 forcibly stops the second conveying section 200, the second workpiece does not advance any more, and the phenomenon that the second workpiece overtakes the first workpiece to collide and cause overlarge deformation of the pump foot bolt 11 is avoided; when the actual conveying speed of the first workpiece is restored to V1 > 0.8Vb, the second conveying section 200 automatically restores to normal operation. The process realizes that the assembly line of the air conditioner compressor is automatically started and stopped according to the conveying speed of the workpieces, avoids the situation that the pump foot bolt 11 is bent due to collision of the front and the rear workpieces, and controls the source of noise generated by an air conditioner external unit.

the quality of the air conditioner external unit produced by the air conditioner compressor assembly line and the control method is reliable, the phenomenon of extrusion and clamping cannot occur between the pump foot bolt 11 of the compressor and a chassis of the air conditioner external unit, vibration is prevented from being transmitted outside through the pump foot bolt 11 through normal damping of the damping foot pad during the operation of the compressor, the noise reduction target is finally achieved, and user experience is improved.

Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.