阅读说明：本技术 一种带减震的超薄agv用差速驱动装置 (Take absorbing ultra-thin differential drive for AGV ) 是由 庞军舰 曹辉 朴永灿 黄大巍 李传州 于 2021-03-12 设计创作，主要内容包括：本发明公开了一种带减震的超薄AGV用差速驱动装置,包括旋转摆动机构、驱动行走机构、直线导轨与弹簧减震机构,所述驱动行走机构为两套,所述直线导轨为四条,所述弹簧减震机构为四套,所述旋转摆动机构的四角均铰接一个所述的弹簧减震机构的上端,两套所述的驱动行走机构为中心对称安装,四套所述的弹簧减震机构的下端分别铰接由两套驱动行走机构组成的四边形的四角,四条所述的直线导轨分为两组,每组所述的直线导轨分别固定安装驱动行走机构的内侧壁；模块化设计,便于组装；结构紧凑,荷载能力强,两套驱动装置成组使用,增加可驱动载荷；整体高度低,适用于强。采用此装置,AGV本体高度可做到120mm以下。为低底盘汽车搬运AGV提供一种解决方案。(The invention discloses a shock-absorbing differential driving device for an ultrathin AGV (automatic guided vehicle), which comprises two sets of driving and traveling mechanisms, four sets of linear guide rails and four sets of spring shock-absorbing mechanisms, wherein the four corners of each driving and traveling mechanism are hinged with the upper end of one spring shock-absorbing mechanism, the two sets of driving and traveling mechanisms are installed in a centrosymmetric manner, the lower ends of the four sets of spring shock-absorbing mechanisms are respectively hinged with the four corners of a quadrangle formed by the two sets of driving and traveling mechanisms, the four sets of linear guide rails are divided into two sets, and the inner side walls of the driving and traveling mechanisms are respectively and fixedly installed on each set of linear guide rails; the modular design is convenient for assembly; the structure is compact, the load capacity is strong, and the two sets of driving devices are used in a group, so that the drivable load is increased; the whole height is low, and the device is suitable for strong. By adopting the device, the height of the AGV body can be below 120 mm. A solution is provided for transporting an AGV by a low-chassis automobile.)

1. The utility model provides a take absorbing ultra-thin differential drive device for AGV, includes rotary swing mechanism (1), drive running gear (2), linear guide (3) and spring damper (4), drive running gear (2) are two sets, linear guide (3) are four, spring damper (4) are four sets, its characterized in that: the four corners of rotatory swing mechanism (1) all articulate one the upper end of spring damper (4), two sets of actuating running gear (2) install for central symmetry, four sets of spring damper (4) the lower extreme articulate the tetragonal four corners of constituteing by two sets of actuating running gear (2) respectively, four linear guide (3) divide into two sets ofly, every group linear guide (3) the inside wall of fixed mounting actuating running gear (2) respectively, the lateral wall and the linear guide (3) sliding fit of rotatory swing structure (1).

2. The differential drive apparatus of claim 1, wherein: rotatory swing mechanism (1) supports (11), supporting seat (12) and swing seat (13) including the gyration, the gyration supports the up end of (11) fixed mounting and supporting seat (12), the both ears seat centre gripping swing seat (13) of supporting seat (12), the lateral wall of swing seat (13) rotates installs gleitbretter bearing (14), oscillating axle (15) are installed to gleitbretter bearing (14) internal rotation, the ear seat of card (16) fixed mounting supporting seat (12) is passed through to the outer end of oscillating axle (15).

3. The differential drive apparatus of claim 2, wherein: slewing bearing (11) include outer loop (111) and inner ring (112), outer loop (111) and inner ring (112) slip ring cover installation, the connecting hole has all been seted up with inner ring (112) in outer loop (111), the connecting hole of outer loop (111) passes through screw rod fixed mounting supporting seat (12) up end, the outside AGV structure of screw rod fixed connection is passed through to the connecting hole of inner ring (112).

4. The differential drive apparatus of claim 1, wherein: the driving travelling mechanism (2) comprises a motor (21), a reduction gearbox (22) and a travelling wheel (23), the output end of the motor (21) is directly connected with the input end of the reduction gearbox (22), the motor (21) is perpendicular to the reduction gearbox (22), the travelling wheel (23) is fixedly provided with the output end of the reduction gearbox (22), and the output end of the reduction gearbox (22) is opposite to the motor (21).

5. The differential drive apparatus of claim 1, wherein: the output ends of the two sets of driving walking mechanisms (2) are positioned on the same axis, and the axis is vertically intersected with the rotating shaft of the rotary swing mechanism (1).

6. The differential drive apparatus of claim 4, wherein: the reduction gearbox (22) comprises a box body (221), a first gear pair (222), a second gear pair (223), a rolling bearing (224), a first transmission shaft (225), a second transmission shaft (226), an end cover (227), a first shaft sleeve (228) and a second shaft sleeve (229), wherein the first gear pair comprises a first pinion (2221) and a first gearwheel (2222), the second gear pair (223) comprises a second pinion (2231) and a second gearwheel (2232), the first pinion (2221) is connected with the output end of the motor reducer (21) through a shaft key, the first gearwheel (2222) and the second pinion (2231) are fixedly installed on the first transmission shaft (225) through shaft keys, the second gearwheel (2232) is fixedly installed on the second transmission shaft (226) through a shaft key, the left end of the second transmission shaft (226) rotates to penetrate through the side wall of the box body (221) and then is fixedly installed with a travelling wheel (23), the right end of the second transmission shaft (226) rotates the other side wall of the installation box body (221), the two ends of the first transmission shaft (225) respectively rotate the side wall of the installation box body (221), a rolling bearing (224) is arranged between the first transmission shaft (225) and the second transmission shaft (226) and the box body (221), the first transmission shaft (225) is sleeved with a first shaft sleeve (228), the second transmission shaft (226) is sleeved with a second shaft sleeve (229), and end covers (227) are clamped at the outer ends of the first transmission shaft (225) and the second transmission shaft (226).

7. The differential drive apparatus of claim 6, wherein: the box body (221) comprises a travelling wheel mounting plate (2211), a motor mounting plate (2212), a first side plate (2213), a second side plate (2214), an upper cover plate (2215), a lower cover plate (2216) and an organic glass plate (2217), wherein the travelling wheel mounting plate (2211) is parallel to the motor mounting plate (2212), the first side plate (2214) is parallel to the second side plate (2215), the upper cover plate (2215) is parallel to the lower cover plate (2216), the edge of the travelling wheel mounting plate (2211), the edge of the motor mounting plate (2212), the edge of the first side plate (2213), the edge of the second side plate (2214), the edge of the upper cover plate (2215) and the edge of the lower cover plate (2216) are fixedly mounted with each other, an observation window is formed in the upper cover plate (2215), and the organic glass plate (2217) is embedded in the observation window.

8. The differential drive apparatus of claim 1, wherein: the spring damping mechanism (4) comprises a spring guide pin (41), a guide pin seat (42), a guide pin sleeve (43), a spring (44), a thin round nut (45), a first hinge pin (46) and a second hinge pin (47), one end of the spring guide pin (41) is screwed at one end of the guide pin seat (42), one end of the guide pin sleeve (43) is a sleeve, the sleeve is slidably mounted with the other end of the spring guide pin (42), the spring (44) is clamped between the guide pin seat (42) and the guide pin sleeve (43), the guide pin sleeve (43) and the spring guide pin (41) are sleeved with the spring (44), the thin round nut (45) is screwed on the outer wall of the sleeve of the guide pin sleeve (43), the number of the thin round nuts (45) is two, a first boss is integrally formed at the other end of the guide pin seat (42), and the first hinge pin (46) is embedded in the first boss, and a second boss is integrally formed at the other end of the guide pin sleeve (43), and a second hinge pin (47) is embedded in the second boss.

9. The differential drive apparatus of claim 2, wherein: the upper edge of the side wall of the swinging seat (13) is fixedly provided with a polyurethane block (17), and the upper surface of the polyurethane block (17) is in contact with the lower end surface of the supporting seat (12).

10. The differential drive apparatus of claim 8, wherein: and nylon gaskets (48) are clamped on the first bosses of the guide pin seats (42) and the second bosses of the guide pin sleeves (43).

Technical Field

The invention relates to the technical field of AGV, in particular to a differential driving device with shock absorption function for an ultrathin AGV.

Background

At present, an AGV which can automatically drill into a vehicle bottom and lift a tire is urgently needed by a parking system and an automobile factory, particularly, the AGV is used for carrying automobiles with the body not higher than 120mm and the lifting capacity of 3 tons and is used for carrying various types of automobiles in different places. This type of AGV has high demands on the differential drive. The differential drive device of the existing AGV has the following defects: low height and high load capacity can not possess simultaneously, and the differential drive arrangement load capacity of low height is than weak, and some have cancelled damper in order to reduce the height moreover, and this kind of differential drive arrangement is often used for little load low height AGV. The differential driving device with high load capacity has a relatively high structure, and is commonly used for high-load AGV with low requirement on height.

Disclosure of Invention

The invention aims to provide a differential driving device with shock absorption for an ultrathin AGV, which aims to solve the problems in the background technology.

In order to achieve the purpose, the invention provides the following technical scheme:

the utility model provides a take absorbing ultra-thin differential drive device for AGV, includes rotatory swing mechanism, driving running gear, linear guide and spring damper, driving running gear is two sets, linear guide is four, spring damper is four sets, rotatory swing mechanism's four corners all articulates one spring damper's upper end, two sets driving running gear install for central symmetry, four sets spring damper's lower extreme articulate the tetragonal four corners of constituteing by two sets of driving running gear respectively, four linear guide divide into two sets ofly, every group linear guide fixed mounting driving running gear's inside wall respectively, rotatory swing structure's lateral wall and linear guide sliding fit.

Preferably, rotatory swing mechanism includes that the gyration is supported, supporting seat and swing seat, the gyration is supported the up end of fixed mounting and supporting seat, the both ears seat centre gripping swing seat of supporting seat, swing seat's lateral wall rotates and installs the gleitbretter bearing, the oscillating axle is installed to the gleitbretter bearing internal rotation, the ear seat of card fixed mounting supporting seat is passed through to the outer end of oscillating axle.

Preferably, slewing bearing includes outer loop and inner ring, outer loop and inner ring slip ring cover installation, the connecting hole has all been seted up to outer loop and inner ring, the connecting hole of outer loop passes through screw rod fixed mounting supporting seat up end, the outside AGV structure of screw rod fixed connection is passed through to inner ring connecting hole.

Preferably, the driving travelling mechanism comprises a motor, a reduction gearbox and a travelling wheel, the output end of the motor is directly connected with the input end of the reduction gearbox, the motor is perpendicular to the reduction gearbox, the travelling wheel is fixedly installed at the output end of the reduction gearbox, and the output end of the reduction gearbox is opposite to the motor.

Preferably, the output ends of the two sets of driving travelling mechanisms are positioned on the same axis, and the axis is vertically intersected with the rotating shaft of the rotary swing mechanism.

Preferably, the reduction gearbox comprises a box body, a first gear pair, a second gear pair, a rolling bearing, a first transmission shaft, a second transmission shaft, an end cover, a first shaft sleeve and a second shaft sleeve, the first gear pair comprises a first pinion and a first gearwheel, the second gear pair comprises a second pinion and a second gearwheel, the first pinion is connected with the output end of the motor reducer through a shaft key, the first gearwheel and the second pinion are fixedly arranged on the first transmission shaft through a shaft key, the second gearwheel is fixedly arranged on the second transmission shaft through a shaft key, a walking wheel is fixedly arranged at the left end of the second transmission shaft after the left end of the second transmission shaft rotatably penetrates through the side wall of the box body, the other side wall of the box body is rotatably arranged at the right end of the second transmission shaft, the two ends of the first transmission shaft are respectively rotatably arranged on the side wall of the box body, and the rolling bearing is arranged between the first transmission shaft and the box body, the first transmission shaft is sleeved with a first shaft sleeve, the second transmission shaft is sleeved with a second shaft sleeve, and end covers are clamped at the outer ends of the first transmission shaft and the second transmission shaft.

Preferably, the box includes walking wheel mounting panel, motor mounting panel, first curb plate, second curb plate, upper cover plate, lower apron and organic glass board, the walking wheel mounting panel is parallel to each other with the motor mounting panel, first curb plate is parallel to each other with the second curb plate, the upper cover plate is parallel to each other with the lower apron, the edge of walking wheel mounting panel, the edge of motor mounting panel, the edge of first curb plate, the edge of second curb plate, the edge of upper cover plate and the mutual fixed mounting in edge of lower apron, the observation window has been seted up to the upper cover plate, organic glass board inlays and adorns in the observation window.

Preferably, the spring damping mechanism comprises a spring guide pin, a guide pin seat, a guide pin sleeve, a spring, a thin round nut, a first hinge pin and a second hinge pin, one end of the spring guide pin is screwed at one end of the guide pin seat, one end of the guide pin sleeve is a sleeve, the sleeve and the other end of the spring guide pin are slidably mounted, the spring is clamped between the guide pin seat and the guide pin sleeve, the spring is sleeved on the guide pin sleeve and the spring guide pin, the thin round nut is screwed on the outer wall of the sleeve of the guide pin sleeve, the number of the thin round nuts is two, a first boss is integrally formed at the other end of the guide pin seat, the first boss is embedded with the first hinge pin, a second boss is integrally formed at the other end of the guide pin sleeve, and the second hinge pin is embedded with the second hinge pin.

Preferably, a polyurethane block is fixedly mounted on the upper edge of the side wall of the swinging seat, and the upper surface of the polyurethane block contacts with the lower end surface of the supporting seat.

Preferably, the first boss of the guide pin seat and the second boss of the guide pin sleeve are both clamped with nylon gaskets.

Compared with the prior art, the invention has the beneficial effects that:

1, modular design, convenient to assemble.

2. Compact structure, load capacity is strong, and two sets of drive arrangement use in groups, increase and to drive load.

3. The whole height is low, and the device is suitable for strong. By adopting the device, the height of the AGV body can be below 120 mm. A solution is provided for transporting an AGV by a low-chassis automobile.

Drawings

FIG. 1 is a perspective view of an embodiment of the present invention;

FIG. 2 is an exploded view of a rotary oscillating mechanism provided by an embodiment of the present invention;

FIG. 3 is a top view provided by an embodiment of the present invention;

FIG. 4 is an exploded view of a propulsion unit according to an embodiment of the present invention;

fig. 5 is a sectional view of a spring damper mechanism according to an embodiment of the present invention.

In the figure: a rotary swing mechanism-1, a rotary support-11, an outer ring-111, an inner ring-112, a supporting seat-12, a swing seat-13, a sliding vane bearing-14, a swing shaft-15, a card-16, a polyurethane block-17, a driving walking mechanism-2, a motor-21, a reduction box-22, a box body-221, a walking wheel mounting plate-2211, a motor mounting plate-2212, a first side plate-2213, a second side plate-2214, an upper cover plate-2215, a lower cover plate-2216, an organic glass plate-2217, a first gear pair-222, a first pinion-2221, a first bull gear-2222, a second gear pair-223, a second pinion-2231, a second bull gear-2232, a rolling bearing-224, a first transmission shaft-225, a second pinion-2231, The device comprises a second transmission shaft-226, an end cover-227, a first shaft sleeve-228, a second shaft sleeve-229, a traveling wheel-23, a linear guide rail-3, a spring damping mechanism-4, a spring guide pin-41, a guide pin seat-42, a guide pin sleeve-43, a spring-44, a thin round nut-45, a first hinge pin-46, a second hinge pin-47 and a nylon gasket-48.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1-5, the present invention provides a technical solution: the utility model provides a take absorbing ultra-thin differential drive device for AGV, includes rotatory swing mechanism 1, drive running gear 2, linear guide 3 and spring damper 4, drive running gear 2 is two sets, linear guide 3 is four, spring damper 4 is four sets, the four corners of rotatory swing mechanism 1 is all articulated one spring damper 4's upper end, two sets drive running gear 2 install for central symmetry, four sets spring damper 4's lower extreme articulate the tetragonal four corners of constituteing by two sets of drive running gear 2 respectively, four linear guide 3 divide into two sets ofly, every group linear guide 3 respectively fixed mounting drive running gear 2's inside wall, rotatory swing mechanism 1's lateral wall and linear guide 3 sliding fit.

An external frame body can be formed by the two sets of driving travelling mechanisms 2, the rotating and swinging mechanisms 1 are effectively supported and installed, the linear slide rails 3 linearly limit the sliding of the rotating and swinging mechanisms 1, and the spring damping mechanisms 4 buffer the bumping and shaking generated in the middle layer in the movement process of the device.

Specifically, rotatory swing mechanism 1 includes that the gyration supports 11, supporting seat 12 and swing seat 13, the gyration supports 1 fixed mounting and the up end of supporting seat 12, swing seat 13 is held to two ears seat centre grippings of supporting seat 12, swing seat 13's lateral wall rotates and installs gleitbretter bearing 14, oscillating axle 15 is installed to gleitbretter bearing 14 internal rotation, card 16 fixed mounting supporting seat 12's ear seat is passed through to oscillating axle 15's outer end.

The gyration is supported 11 and is made to connect more conveniently through self structural feature, avoids the substructure to turn to and produces internal stress simultaneously, produces the influence to superstructure, and is connected through gleitbretter bearing 14 and swing axle 15 between supporting seat 12 and swing seat 13 for when swing seat 13 carries out the swing on the level, supporting seat 12 can keep original gesture.

Specifically, slewing bearing 11 includes outer loop 111 and inner ring 112, outer loop 111 and inner ring 112 slip ring cover installation, outer loop 111 and inner ring 112 have all seted up the connecting hole, the connecting hole of outer loop 111 passes through screw rod fixed mounting supporting seat 12 up end, the outside AGV structure of screw rod fixed connection is passed through to the connecting hole of inner ring 112.

The outer ring 111 and the inner ring 112 are sleeved in a rotating mode, so that the whole body can rotate relatively, and the flexibility of connection is improved.

Specifically, the driving travelling mechanism 2 comprises a motor 21, a reduction gearbox 22 and a travelling wheel 23, the output end of the motor 21 is directly connected with the input end of the reduction gearbox 22, the motor 21 is perpendicular to the reduction gearbox 22, the travelling wheel 23 is fixedly provided with the output end of the reduction gearbox 22, and the output end of the reduction gearbox 22 is opposite to the motor 21.

The motor 21 provides power for the movement of the device, the reduction box 22 reduces the speed of the power output by the motor 21, and the walking wheels 23 change the power output by the reduction box into driving force.

Specifically, the output ends of the two sets of the driving and traveling mechanisms 2 are located on the same axis, and the axis is vertically intersected with the rotating shaft of the rotary swing mechanism 1.

The center of gravity of the load of the whole device is coincided and set, so that the load can be effectively and uniformly distributed.

Specifically, the reduction gearbox 22 includes a box 221, a first gear pair 222, a second gear pair 223, a rolling bearing 224, a first transmission shaft 225, a second transmission shaft 226, an end cover 227, a first shaft sleeve 228 and a second shaft sleeve 229, the first gear pair includes a first pinion 2221 and a first gearwheel 2222, the second gear pair 223 includes a second pinion 2231 and a second gearwheel 2232, the first pinion 2221 is connected with the output end of the motor reducer 21 through a shaft key, the first gearwheel 2222 and the second pinion 2231 are both fixedly mounted on the first transmission shaft 225 through a shaft key, the second gearwheel 2232 is fixedly mounted on the second transmission shaft 226 through a shaft key, the left end of the second transmission shaft 226 rotatably penetrates through the side wall of the box 221 and is fixedly mounted with a traveling wheel 23, the other side wall of the box 221 is rotatably mounted on the right end of the second transmission shaft 226, the two ends of the first transmission shaft 225 are rotatably mounted on the side wall of the box 221, rolling bearings 224 are arranged between the first transmission shaft 225 and the second transmission shaft 226 and the box body 221, a first shaft sleeve 228 is sleeved on the first transmission shaft 225, a second shaft sleeve 229 is sleeved on the second transmission shaft 226, and end covers 227 are clamped at the outer ends of the first transmission shaft 225 and the second transmission shaft 226.

The first gear pair 222, the second gear pair 223, the first transmission shaft 225, and the second transmission shaft 226 constitute a two-stage reduction gear, and the ball bearing 224 can reduce friction force, and the first bushing 228 and the second bushing 229 can limit their corresponding gears.

Specifically, the box 221 includes a traveling wheel mounting plate 2211, a motor mounting plate 2212, a first side plate 2213, a second side plate 2214, an upper cover plate 2215, a lower cover plate 2216 and an organic glass plate 2217, the traveling wheel mounting plate 2211 and the motor mounting plate 2212 are parallel to each other, the first side plate 2214 and the second side plate 2215 are parallel to each other, the upper cover plate 2215 and the lower cover plate 2216 are parallel to each other, an edge of the traveling wheel mounting plate 2211, an edge of the motor mounting plate 2212, an edge of the first side plate 2213, an edge of the second side plate 2214, an edge of the upper cover plate 2215 and an edge of the lower cover plate 2216 are fixedly mounted to each other, the upper cover plate 2215 is provided with an observation window, and the organic glass plate 2217.

The travelling wheel mounting plate 2211, the motor mounting plate 2212, the first side plate 2213, the second side plate 2214, the upper cover plate 2215 and the lower cover plate 2216 form a complete shell structure, the internal structure is born and protected, and the observation window is convenient to observe and overhaul.

Specifically, the spring damper mechanism 4 includes a spring guide pin 41, a guide pin holder 42, a guide pin bush 43, a spring 44, a thin round nut 45, a first hinge pin 46 and a second hinge pin 47, one end of the spring guide pin 41 is screwed to one end of the guide pin seat 42, one end of the guide pin sleeve 43 is a sleeve, and the sleeve and the other end of the spring guide pin 42 are installed in a sliding way, a spring 44 is clamped between the guide pin seat 42 and the guide pin sleeve 43, the spring 44 is sleeved with the guide pin sleeve 43 and the spring guide pin 41, the outer wall of the sleeve of the guide pin sleeve 43 is screwed with a thin round nut 45, the number of the thin round nuts 45 is two, the other end of the guide pin seat 42 is integrally formed with a first boss, and a first hinge pin 46 is fitted to the first boss, a second boss is integrally formed at the other end of the guide pin boss 43, and a second hinge pin 47 is fitted to the second boss.

The spring guide pin 41, the guide pin seat 42, the guide pin sleeve 43 and the spring 44 form a main spring damping structure, limit connection is conducted simultaneously, the damping stress direction is limited, the thin round nut 45 can conduct pretightening force adjustment on the spring 44, the first hinge pin 46 is hinged to the side wall of the reduction gearbox 22, and the second hinge pin 47 is hinged to the supporting seat 12.

Specifically, a polyurethane block 17 is fixedly mounted on the upper edge of the side wall of the swing seat 13, and the upper surface of the polyurethane block 17 contacts the lower end surface of the support seat 12.

The polyurethane block 17 is used for isolation, so that the swinging seat 13 is prevented from being in direct contact with the supporting seat 12, and high noise is generated.

Specifically, a nylon washer 48 is interposed between the first boss of the guide pin boss 42 and the second boss of the guide pin boss 43.

The hinging process is additionally clamped.

The working principle is as follows: after the device and the AGV frame are assembled, the motors 21 in the two sets of driving travelling mechanisms 2 are independently adjusted according to different working requirements, the rotating speeds during the execution are the same, the rotating speeds during the turning are different, the device rotates, the structural characteristics of the rotating support 11 are utilized, the rotating torque force is eliminated, when the device jolts, the device vibrates through the spring damping mechanism 4 to eliminate, and meanwhile, the swinging generated is offset through the connecting structure of the swinging seat 13 and the supporting seat 12.

In the description of the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "fixed" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral part; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The standard parts used in the invention can be purchased from the market, the special-shaped parts can be customized according to the description of the specification and the accompanying drawings, the specific connection mode of each part adopts conventional means such as mature bolts, rivets, welding and the like in the prior art, the machines, the parts and equipment adopt conventional models in the prior art, and the circuit connection adopts the conventional connection mode in the prior art, so that the detailed description is omitted.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.