阅读说明：本技术 一种自行走剪叉式移动升降平台电气控制系统 (Electric control system of self-walking scissor-type movable lifting platform ) 是由 向未 宋璋策 邹林江 于 2019-12-03 设计创作，主要内容包括：本发明公开了一种自行走剪叉式移动升降平台电气控制系统,包括整车控制器、马达控制器、以及三相交流永磁同步电机,其中,整车控制器,用于发出使能控制信号；马达控制器与整车控制器相连,用于根据整车控制器发出的使能控制信号,输出开关信号；三相交流永磁同步电机分别与马达控制器和自行走剪叉式移动升降平台上的齿轮泵相连,用于根据马达控制器输出的开关信号,启动或停止齿轮泵动作,以带动或停止向液压系统输出动力。本发明公开的自行走剪叉式移动升降平台电气控制系统,转矩稳定、调速性能好；效率高、发热小；高效节能、大大提升整体的续航能力；防护等级高、体积小、给设计布局带来了更大的自由性和发挥空间。(The invention discloses an electric control system of a self-walking scissor-fork type mobile lifting platform, which comprises a vehicle control unit, a motor controller and a three-phase alternating current permanent magnet synchronous motor, wherein the vehicle control unit is used for sending out an enabling control signal; the motor controller is connected with the vehicle control unit and used for outputting a switching signal according to an enabling control signal sent by the vehicle control unit; the three-phase alternating current permanent magnet synchronous motor is respectively connected with the motor controller and a gear pump on the self-walking scissor type mobile lifting platform and used for starting or stopping the gear pump to act according to a switching signal output by the motor controller so as to drive or stop outputting power to the hydraulic system. The electric control system of the self-walking scissor-fork type mobile lifting platform disclosed by the invention has the advantages of stable torque and good speed regulation performance; the efficiency is high and the heat generation is small; the energy is saved efficiently, and the integral cruising ability is greatly improved; the protection level is high, the volume is small, and greater freedom and play space are brought to the design layout.)

1. An electrical control system of a self-walking scissor-type mobile lifting platform is applied to the self-walking scissor-type mobile lifting platform, the self-walking scissor-type mobile lifting platform comprises a hydraulic system, a gear pump is arranged on the hydraulic system, and the electrical control system of the self-walking scissor-type mobile lifting platform is characterized by comprising a whole vehicle controller (10), a motor controller (20) and a three-phase alternating current permanent magnet synchronous motor (30), wherein,

the vehicle control unit (10) is used for sending out an enabling control signal;

the motor controller (20) is connected with the vehicle control unit (10) and is used for outputting a switching signal according to the enabling control signal sent by the vehicle control unit (10);

the three-phase alternating current permanent magnet synchronous motor (30) is respectively connected with the motor controller (20) and a gear pump on the self-walking scissor type mobile lifting platform and used for controlling the gear pump to act according to the switching signal output by the motor controller (20) so as to drive or stop the gear pump to output power to the hydraulic system.

2. A self-propelled scissor-like mobile lift platform electrical control system as claimed in claim 1,

the motor controller (20) comprises a comparison module (21) and a control module (22),

the comparison module (21) is used for comparing the voltage in the enabling control signal sent by the vehicle control unit (10) with a preset threshold voltage;

the control module (22) is connected with the comparison module (21) and used for outputting a switching signal according to the comparison result of the comparison module (21).

3. A self-propelled scissor-like mobile lift platform electrical control system as claimed in claim 2,

the switching signal comprises a start signal and a stop signal, the control module (22) comprises a first control unit (221) and a second control unit (222),

the first control unit (221) is connected to the comparison module (21) and configured to output a start signal to activate the motor controller (20) if a voltage in the enable control signal is greater than or equal to the threshold voltage;

the second control unit (222) is connected with the comparison module (21) and used for outputting a stop signal if the voltage in the enable control signal is smaller than the threshold voltage.

4. A self-propelled scissor-like mobile lift platform electrical control system as claimed in claim 3,

the first control unit (221) further comprises a speed regulation subunit (2211),

the vehicle control unit (10) is also used for sending a speed control signal after the motor controller (20) is activated;

the speed regulation subunit (2211) is connected with the vehicle control unit (10) and is used for outputting waveforms with corresponding frequencies to the three-phase alternating current permanent magnet synchronous motor (30) according to the voltage of the speed control signal sent by the vehicle control unit (10) and regulating the rotating speed of the three-phase alternating current permanent magnet synchronous motor (30).

5. A self-propelled scissor mobile lift platform electrical control system as claimed in claim 3 or 4,

a position sensor (31) is arranged at the rotor shaft end of the three-phase alternating current permanent magnet synchronous motor (30), the motor controller (20) further comprises a voltage output module (24) and a monitoring module (23),

the voltage output module (24) is used for supplying power to the voltage output module (24);

the position sensor (31) is connected with the monitoring module (23) and is used for detecting the rotor operation information of the three-phase alternating current permanent magnet synchronous motor (30) and transmitting the rotor operation information back to the monitoring module (23);

and the monitoring module (23) is connected with the position sensor (31) and is used for monitoring the rotor rotating speed and the rotor position of the three-phase alternating current permanent magnet synchronous motor (30) according to the rotor operation information returned by the position sensor (31).

6. A self-propelled scissor-like mobile lift platform electrical control system as recited in claim 5,

the electric control system of the self-walking scissor-type mobile lifting platform also comprises a charger (40) and a rechargeable battery (50),

the charger (40) comprises a detection module (41), a charging controller (42), a charging locking line (43) and a conversion module (44), the rechargeable battery (50) comprises a battery control system (51),

the detection module (41) is used for detecting whether the charger (40) is connected with a power supply voltage or not;

the charging controller (42) is respectively connected with the detection module (41), the charging locking line (43) and the conversion module (44) and is used for disconnecting the charging locking line (43) when the detection module (41) detects that the charger (40) is connected with a power supply voltage; and controls the conversion module (44) to convert the accessed power supply voltage into an activation voltage and output the activation voltage to the battery control system (51);

the battery control system (51) is connected with the conversion module (44) and used for activating the rechargeable battery (50) according to the activation voltage output by the conversion module (44), enabling the charger (40) to establish communication with the rechargeable battery (50), and applying proper voltage and current to the charger (40) according to the self condition.

7. A self-propelled scissor-like mobile lift platform electrical control system as claimed in claim 1,

the electric control system of the self-walking scissor-type mobile lifting platform also comprises a power supply main switch (60) and a fuse (70),

the power supply main switch (60) is arranged on a negative connecting line of the rechargeable battery (50) and the motor controller (20), and the fuse (70) is arranged on a positive connecting line of the rechargeable battery (50) and the motor controller (20).

8. A self-propelled scissor-like mobile lift platform electrical control system as recited in claim 7,

the rechargeable battery (50) further comprises a relay (52) connected to the motor controller (20),

and the battery control system (51) is connected with the relay (52) and is used for supplying a voltage signal to a key output end on the charger (40) when the power supply main switch (60) is opened, controlling the relay (52) to pull in and supplying energy to the motor controller (20).

9. A self-propelled scissor-like mobile lift platform electrical control system as recited in claim 8,

the charger (40) is in communication connection with the rechargeable battery (50) through a CAN bus.

10. A self-propelled scissor-like mobile lift platform electrical control system as recited in claim 9,

the rechargeable battery (50) is in communication connection with the vehicle control unit (10) through a CAN bus.

Technical Field

The invention relates to the technical field of lifting platforms, and particularly discloses an electrical control system of a self-walking scissor-type mobile lifting platform.

Background

The self-walking scissor-type movable lifting platform can be used for high-altitude operation in various industries, and has the characteristic of self-walking, so that a large amount of time and manpower are saved for high-altitude operation. In the industry, a simple and economic direct current series excited motor is always used as a power source, and although the direct current series excited motor has large starting torque and strong overload capacity, the direct current series excited motor also has the defects of unstable torque, poor speed regulation performance, lower efficiency, larger heat generation and lower protection capacity.

Therefore, the existing self-walking scissor-type mobile lifting platform using a direct-current series excited motor as a power source has the defects of unstable torque, poor speed regulation performance, low efficiency, high heat generation and low protection capability, and is a technical problem to be solved urgently.

Disclosure of Invention

The invention provides an electrical control system of a self-walking scissor-type mobile lifting platform, and aims to solve the technical problems of unstable torque, poor speed regulation performance, low efficiency, high heat generation and low protection capability of the conventional self-walking scissor-type mobile lifting platform using a direct-current series excitation motor as a power source.

The invention discloses an electric control system of a self-walking scissor-fork type mobile lifting platform, which comprises a vehicle control unit, a motor controller and a three-phase alternating current permanent magnet synchronous motor, wherein,

the vehicle control unit is used for sending out an enabling control signal;

the motor controller is connected with the vehicle control unit and used for outputting a switching signal according to an enabling control signal sent by the vehicle control unit;

the three-phase alternating current permanent magnet synchronous motor is respectively connected with the motor controller and a gear pump on the self-walking scissor type mobile lifting platform and used for controlling the gear pump to act according to a switching signal output by the motor controller so as to drive or stop the gear pump to output power to the hydraulic system.

Further, the motor controller comprises a comparison module and a control module,

the comparison module is used for comparing the voltage in the enabling control signal sent by the whole vehicle controller with a preset threshold voltage;

the control module is connected with the comparison module and used for outputting a switching signal according to a comparison result of the comparison module.

Further, the switch signal comprises a start signal and a stop signal, the control module comprises a first control unit and a second control unit,

the first control unit is connected with the comparison module and used for outputting a starting signal and activating the motor controller to act if the voltage in the enabling control signal is greater than or equal to the threshold voltage;

the second control unit is connected with the comparison module and used for outputting a stop signal if the voltage in the enabling control signal is smaller than the threshold voltage.

Furthermore, the first control unit also comprises a speed regulation subunit,

the vehicle control unit is also used for sending a speed control signal after the motor controller is activated;

and the speed regulating subunit is connected with the vehicle control unit and used for outputting a waveform with corresponding frequency to the three-phase alternating current permanent magnet synchronous motor according to the voltage of the speed control signal sent by the vehicle control unit and regulating the rotating speed of the three-phase alternating current permanent magnet synchronous motor.

Furthermore, a position sensor is arranged at the rotor shaft end of the three-phase alternating current permanent magnet synchronous motor, the motor controller also comprises a voltage output module and a monitoring module,

the voltage output module is used for supplying power to the voltage output module;

the position sensor is connected with the monitoring module and used for detecting the rotor operation information of the three-phase alternating current permanent magnet synchronous motor and transmitting the rotor operation information back to the monitoring module;

the monitoring module is connected with the position sensor and used for monitoring the rotor rotating speed and the rotor position of the three-phase alternating current permanent magnet synchronous motor according to the rotor operation information returned by the position sensor.

Furthermore, the electric control system of the self-walking scissor-type mobile lifting platform also comprises a charger and a rechargeable battery,

the charger comprises a detection module, a charging controller, a charging locking line and a conversion module, the rechargeable battery comprises a battery control system,

the detection module is used for detecting whether the charger is connected with a power supply voltage or not;

the charging controller is respectively connected with the detection module, the charging locking line and the conversion module and is used for disconnecting the charging locking line when the detection module detects that the charger is connected with the power supply voltage; the control conversion module converts the accessed power supply voltage into an activation voltage and outputs the activation voltage to the battery control system;

the battery control system is connected with the conversion module and used for activating the rechargeable battery according to the activation voltage output by the conversion module, so that the charger and the rechargeable battery establish communication, and apply proper voltage and current to the charger according to the self condition.

Furthermore, the electric control system of the self-walking scissor-type mobile lifting platform also comprises a main power switch and a fuse,

the power supply main switch is arranged on a negative connecting wire of the rechargeable battery and the motor controller, and the fuse is arranged on a positive connecting wire of the rechargeable battery and the motor controller.

Further, the rechargeable battery also comprises a relay connected with the motor controller,

the battery control system is connected with the relay and used for supplying a voltage signal to the key output end on the charger when the power supply main switch is turned on, controlling the relay to be closed and supplying energy to the motor controller.

Further, the charger is in communication connection with the rechargeable battery through a CAN bus.

Furthermore, the rechargeable battery is in communication connection with the vehicle control unit through a CAN bus.

The self-walking scissor-type mobile lifting platform electric control system provided by the invention has the following beneficial effects:

the invention discloses an electric control system of a self-walking scissor-type mobile lifting platform, which adopts a vehicle control unit, a motor controller and a three-phase alternating current permanent magnet synchronous motor. Simultaneously, compare in traditional driving system, PMSM is efficient, generate heat for a short time, and high-efficient energy-conserving lithium cell on the collocation, holistic duration will promote greatly. In addition, the permanent magnet synchronous motor has higher IP protection level and smaller volume, and brings more freedom and exertion space for design layout. The electric control system of the self-walking scissor-fork type mobile lifting platform disclosed by the invention has the advantages of stable torque and good speed regulation performance; the efficiency is high and the heat generation is small; the energy is saved efficiently, and the integral cruising ability is greatly improved; the protection level is high, the volume is small, and greater freedom and play space are brought to the design layout.

Drawings

FIG. 1 is a functional block diagram of a first embodiment of a self-propelled scissor-type mobile lift platform electrical control system provided by the present invention;

FIG. 2 is a functional block diagram of an embodiment of the motor controller of FIG. 1;

FIG. 3 is a functional block diagram of an embodiment of the motor control module of FIG. 2;

FIG. 4 is a schematic diagram of a control module of the motor controller of FIG. 1 interacting with a three-phase AC PMSM;

FIG. 5 is a functional block diagram of a second embodiment of a self-propelled scissor-type mobile lift platform electrical control system provided by the present invention;

FIG. 6 is a schematic diagram of the control module of FIG. 5 when the charger interacts with the rechargeable battery.

The reference numbers illustrate:

10. a vehicle control unit; 20. a motor controller; 30. a three-phase alternating current permanent magnet synchronous motor; 21. a comparison module; 22. a control module; 221. a first control unit; 222. a second control unit; 2211. a speed regulation subunit; 31. a position sensor; 23. a monitoring module; 40. a charger; 50. a rechargeable battery; 41. a detection module; 42. a charge controller; 43. charging a vehicle locking line; 44. a conversion module; 51. a battery control system; 60. a power supply main switch; 70. a fuse; 52. a relay.

Detailed description of the preferred embodiments

In order to better understand the technical solution, the technical solution will be described in detail with reference to the drawings and the specific embodiments.

As shown in fig. 1, fig. 1 is a functional block diagram of a first embodiment of an electrical control system for a self-walking scissor-type mobile lifting platform provided by the present invention, in the first embodiment, the electrical control system for a self-walking scissor-type mobile lifting platform includes a vehicle controller 10, a motor controller 20, and a three-phase ac permanent magnet synchronous motor 30, wherein the vehicle controller 10 is configured to send an enable control signal; the motor controller 20 is connected with the vehicle control unit 10 and is used for outputting a switching signal according to an enabling control signal sent by the vehicle control unit 10; the three-phase alternating current permanent magnet synchronous motor 30 is respectively connected with the motor controller 20 and a gear pump on the self-walking scissor type mobile lifting platform, and is used for controlling the gear pump to act according to a switching signal output by the motor controller 20 so as to drive or stop the gear pump to output power to the hydraulic system. In this embodiment, the switching signal includes an on signal and an off signal, and the motor controller 20 correspondingly outputs the on signal or the off signal according to the voltage of the enable control signal sent by the vehicle control unit 10; the three-phase alternating current permanent magnet synchronous motor 30 controls the starting action of the gear pump according to the starting signal output by the motor controller 20 so as to drive the gear pump to output power to the hydraulic system; or the three-phase alternating current permanent magnet synchronous motor 30 controls the gear pump to stop according to the closing signal output by the motor controller 20 so as to stop the power output from the gear pump to the hydraulic system.

In the above structure, please refer to fig. 2 and fig. 3, the motor controller 20 includes a comparing module 21 and a control module 22, wherein the comparing module 21 is configured to compare a voltage in an enable control signal sent by the vehicle controller 10 with a preset threshold voltage; the control module 22 is connected to the comparison module 21 and configured to output a switching signal according to a comparison result of the comparison module 21. In this embodiment, the switching signal includes a start signal and a stop signal, the control module 22 includes a first control unit 221 and a second control unit 222, the first control unit 221 is connected to the comparison module 21, and is configured to output the start signal and activate the motor controller 20 to operate if a voltage in the enable control signal is greater than or equal to a threshold voltage; the second control unit 222 is connected to the comparing module 21, and configured to output a stop signal if the voltage in the enable control signal is smaller than the threshold voltage. Preferably, the first control unit 221 further includes a speed regulation subunit 2211, and the vehicle control unit 10 is further configured to send a speed control signal after activating the motor controller 20; and the speed regulating subunit 2211 is connected to the vehicle controller 10, and is configured to output a waveform with a corresponding frequency to the three-phase ac permanent magnet synchronous motor 30 according to a voltage of a speed control signal sent by the vehicle controller 10, so as to regulate a rotation speed of the three-phase ac permanent magnet synchronous motor 30. In the embodiment, the vehicle control unit 10 outputs a switching signal to the motor controller 20, the motor controller 20 is activated to operate, the vehicle control unit 10 outputs a speed control signal, the motor controller 20 outputs a waveform with a corresponding frequency from U, V, W three phases to the three-phase ac permanent magnet synchronous motor 30 according to the voltage in the speed control signal, and the three-phase ac permanent magnet synchronous motor 30 starts to operate and drives the gear pump to smoothly output power to the hydraulic system.

Preferably, referring to fig. 4, in the electrical control system for a self-walking scissor-type mobile lifting platform provided in this embodiment, a position sensor 31 is disposed at a rotor shaft end of the three-phase ac permanent magnet synchronous motor 30, the motor controller 20 further includes a voltage output module 24 and a monitoring module 23, and the voltage output module 24 is configured to supply power to the voltage output module 24; the position sensor 31 is connected with the monitoring module 23 and is used for detecting the rotor operation information of the three-phase alternating current permanent magnet synchronous motor 30 and transmitting the rotor operation information back to the monitoring module 23; the monitoring module 23 is connected to the position sensor 31, and is configured to monitor the rotor speed and the rotor position of the three-phase ac permanent magnet synchronous motor 30 according to the rotor operation information returned by the position sensor 31. In the present embodiment, the position sensor 31 is a hall sensor, and other sensors, such as an optoelectronic crankshaft and camshaft position sensor, are also within the protection scope of the present patent.

Further, as shown in fig. 5 and fig. 6, the electrical control system for a self-walking scissor-type mobile lifting platform provided by this embodiment further includes a charger 40 and a rechargeable battery 50, where the charger 40 includes a detection module 41, a charging controller 42, a charging locking line 43 and a conversion module 44, and the rechargeable battery 50 includes a battery control system 51, where the detection module 41 is used to detect whether the charger 40 is connected to a power supply voltage; the charging controller 42 is respectively connected to the detection module 41, the charging locking line 43 and the conversion module 44, and is configured to disconnect the charging locking line 43 when the detection module 41 detects that the charger 40 is connected to the power supply voltage; and controls the conversion module 44 to convert the accessed power supply voltage into an activation voltage and output the activation voltage to the 51; the battery control system 51 is connected to the converting module 44, and is configured to activate the rechargeable battery 50 according to the activation voltage output by the converting module 44, so that the charger 40 establishes communication with the rechargeable battery 50, and applies a suitable voltage and current to the charger 40 according to the self condition. The rechargeable battery 50 may be a lithium battery, or may be other batteries, such as a nickel metal hydride battery, and so on, and all of them are within the protection scope of this patent. In this embodiment, the rechargeable battery 50 can be charged to a suitable capacity after several different charging phases, thereby fully utilizing the charge of the battery and ensuring a long life of the battery.

In addition, the electrical control system for the self-walking scissor-fork type mobile lifting platform provided by the embodiment further comprises a power main switch 60 and a fuse 70, wherein the power main switch 60 is installed on a negative connecting line of the rechargeable battery 50 and the motor controller 20, and the fuse 70 is installed on a positive connecting line of the rechargeable battery 50 and the motor controller 20. The charger 40 is connected with the rechargeable battery 50 through CAN bus communication. The rechargeable battery 50 is in communication connection with the vehicle control unit 10 through a CAN bus. The rechargeable battery 50 further includes a relay 52 connected to the motor controller 20, and a battery control system 51 connected to the relay 52 for supplying a voltage signal to the key output of the charger 40 when the power master switch 60 is turned on, controlling the relay 52 to engage and provide power to the motor controller 20 to ensure the safety of the circuit and the self-propelled scissor-lift platform.

As shown in fig. 1 to 6, the principle of the electrical control system for the self-walking scissor-type mobile lifting platform provided by the present embodiment is as follows:

in the embodiment, the charger 40 includes a locking line with pins 4P and 5P, and the charger 40 with CAN communication and the rechargeable battery 50 provide clean and efficient energy for the whole system. The rechargeable battery 50 can communicate with the vehicle control unit 10 through the pin 1B and the pin 1C; the rechargeable battery 50 can be externally activated through pin 3P; the fuse 70 is installed on a positive connection line of the rechargeable battery 50 and the motor controller 20; the power main switch 60 is installed on the negative connection line of the rechargeable battery 50 and the motor controller 20; the motor controller 20 detects the rotating speed and the rotor position of the three-phase alternating current permanent magnet synchronous motor 30 through a position sensor 31 (a 5-wire Hall sensor); the vehicle control unit 10 sends a 24V enabling control signal to the motor controller 20; the vehicle control unit 10 sends a 0-5V speed control signal to the motor controller 20, so as to control the rotating speed of the three-phase alternating current permanent magnet synchronous motor 30.

When charging, 220V alternating current is connected into the charger 40, and the charging lock car lines 4P and 5P are disconnected, prevent to start in the charging process from walking scissors fork formula removal lift platform. The charger 40 internally draws a 12V supply to the battery control system in the rechargeable battery 50 through pins 3D and 4D. After the battery control system is activated, the charger 40 and the rechargeable battery 50 start to establish communication, and the rechargeable battery 50 can apply appropriate voltage and current to the charger 40 according to various conditions of the rechargeable battery 50. After several different charging phases, the rechargeable battery 50 can be charged to a suitable capacity to fully utilize the charge of the battery and ensure a long life of the battery.

Before the whole vehicle acts, a power supply main switch 60 is turned on, a voltage signal of 15-30V is provided for a pin 3P, a relay 52 in a rechargeable battery 50 is attracted, and energy is provided for a motor controller 20 through an electric wire with a fuse 70, so that the safety of a circuit and a self-walking scissor-fork type mobile lifting platform is guaranteed. The motor controller 20 supplies power to the position sensor 31 in the three-phase ac pm synchronous machine 30 and receives the return signal to monitor the rotational speed and rotor position of the three-phase ac pm synchronous machine 30. When the vehicle starts to operate, the vehicle control unit 10 outputs a 24V dc enable control signal to the motor controller 20 through the pin 8A, the motor controller 20 operates and activates, then the vehicle control unit 10 outputs a 0-5V dc signal to the motor controller 20 through the pin 9A, the motor controller 20 outputs a waveform with a corresponding frequency from U, V, W three phases to the three-phase ac permanent magnet synchronous motor 30 according to the voltage, and the three-phase ac permanent magnet synchronous motor 30 starts to operate and drives the gear pump to smoothly output power to the hydraulic system. When the voltage signal output to the motor controller 20 by the vehicle control unit 10 through the pin 9A changes, the rotation speed of the three-phase ac permanent magnet synchronous motor 30 also changes, so as to realize speed regulation. When the 24V dc signal output to the motor controller 20 through the pin 8A of the vehicle control unit 10 disappears or is lower than the preset threshold voltage, the motor controller 20 immediately stops outputting to the three-phase ac permanent magnet synchronous motor 30, and the three-phase ac permanent magnet synchronous motor 30 will stop rapidly.

The electric control system of the self-walking scissor-type mobile lifting platform disclosed by the embodiment is compared with the prior art, a vehicle control unit, a motor controller and a three-phase alternating-current permanent magnet synchronous motor are adopted, the self-walking scissor-type mobile lifting platform generally drives a gear pump through a motor to provide pressure for a hydraulic system to realize action, and the permanent magnet synchronous motor is stable in torque and good in speed regulation performance, so that the action can be more smooth, fluent and stable compared with the traditional power system. Simultaneously, compare in traditional driving system, PMSM is efficient, generate heat for a short time, and high-efficient energy-conserving lithium cell on the collocation, holistic duration will promote greatly. In addition, the permanent magnet synchronous motor has higher IP protection level and smaller volume, and brings more freedom and exertion space for design layout. The electric control system of the self-walking scissor-fork type mobile lifting platform disclosed by the embodiment has the advantages of stable torque and good speed regulation performance; the efficiency is high and the heat generation is small; the energy is saved efficiently, and the integral cruising ability is greatly improved; the protection level is high, the volume is small, and greater freedom and play space are brought to the design layout.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention. It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.