SYSTEM FOR CONTROLLING WATERCRAFT AND WATERCRAFT

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese Patent Application No. 2024-201120 filed on Nov. 18, 2024. The entire contents of this application are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to systems for controlling watercraft and watercraft.

2. Description of the Related Art

A position keeping control for keeping a watercraft located at a target spot has been known as a control executed for a watercraft in an automated watercraft operation (see Japan Laid-open Patent Application Publication No. 2023-068838). In the position keeping control, the watercraft, when separated from the target spot, is kept at the target spot as follows: the watercraft is caused to perform bow turning such that the stern or bow thereof is oriented to the target spot, and then the watercraft is moved in the back-and-forth direction.

In the conventional position keeping control, the magnitude of a thrust to be generated by a marine propulsion device is controlled in accordance with the amount of displacement of the watercraft with respect to the target spot in the back-and-forth direction. Because of this, if the watercraft is displaced by a small amount from the target spot in the back-and-forth direction, the thrust to be generated by the marine propulsion device is reduced in magnitude. Thus, it is difficult to cause the watercraft to perform bow turning and it takes time for the watercraft to reach the target spot in some cases. On the other hand, for instance, it can be also assumed that the watercraft is caused to perform bow turning, with the thrust being increased in magnitude. In this case, however, the watercraft is displaced by a large amount from the target spot in the back-and-forth direction. Thus, there is a concern that the accuracy of the position keeping control deteriorates.

SUMMARY OF THE INVENTION

Example embodiments of the present invention enable watercraft to be easily kept at a target spot in a position keeping control executed in an automated watercraft operation and enhance the accuracy of the position keeping control.

A system according to an example embodiment of the present disclosure relates to a system for controlling a watercraft and includes a marine propulsion device and a controller. The marine propulsion device is configured to generate a thrust to propel the watercraft. The marine propulsion device includes an upper portion, a lower portion pivotable about an axis of a steering axle with respect to the upper portion, and a propeller on the lower portion. The controller is configured or programed to execute a position keeping control to control the marine propulsion device such that the watercraft is kept at a target spot by directing either a bow or stern of the watercraft to the target spot and then moving the watercraft toward the target spot. The position keeping control includes a bow turning control to direct either the bow or stern of the watercraft to the target spot. The bow turning control of the position keeping control includes a first bow turning control and a second bow turning control. The first bow turning control controls an output of the marine propulsion device, a rotational direction of the propeller, and a rudder angle to be within a predetermined angular range based on information regarding the target spot of the watercraft and information regarding a position of the watercraft. The second bow turning control controls the rotational direction of the propeller and the rudder angle to be a first angle greater than a maximum rudder angle of the predetermined angular range based on the information regarding the target spot of the watercraft and the information regarding the position of the watercraft. The controller is configured or programed to execute the second bow turning control when predetermined conditions are satisfied in the bow turning control of the position keeping control, and the controller is configured or programmed to execute the first bow turning control when the predetermined conditions are not satisfied in the bow turning control of the position keeping control, the predetermined conditions being a predetermined condition that a difference between a target compass direction of the target spot and a compass direction of the watercraft is greater than or equal to a predetermined value and a predetermined condition that the output of the marine propulsion device is less than or equal to a predetermined first output.

In a system according an example embodiment of the present invention, the lower portion is pivotable about the axis of the steering axle with respect to the upper portion. Thus, the marine propulsion device is able to have a wider range of rudder angles than, for instance, a type of marine propulsion device in which lower portion pivots together with the upper portion. Additionally, in the bow turning control of the position keeping control, the controller is configured or programmed to execute the second bow turning control to control the rudder angle to be the first angle greater than the maximum rudder angle in the first bow turning control when the following predetermined conditions are satisfied: the predetermined condition that the difference between the target compass direction of the target spot and the compass direction of the watercraft is greater than or equal to the predetermined value and the condition that the output of the marine propulsion device is less than or equal to the predetermined first output. In the second bow turning control, the watercraft is able to perform bow turning substantially on the spot. Thus, even when the watercraft is displaced from the target spot by a small amount in the back-and-forth direction, the watercraft is able to perform bow turning toward the target spot, while the watercraft is prevented from being greatly displaced in the back-and-forth direction. As a result, in the position keeping control, the watercraft is able to be easily kept at the target spot. Additionally, it is possible to enhance the accuracy of the position keeping control.

According to example embodiments of the present invention, watercraft are able to be easily kept at a target spot in a position keeping control executed in an automated watercraft operation. Additionally, it is possible to enhance the accuracy of the position keeping control.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the example embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a watercraft to which a marine propulsion device is mounted according to an example embodiment of the present invention.

FIG. 2 is a side view of the marine propulsion device.

FIG. 3 is a diagram for explaining an electric motor.

FIG. 4 is a schematic diagram showing a configuration of a watercraft operating system.

FIG. 5 is a front view of a joystick.

FIG. 6 is a diagram showing a series of motions of the watercraft during a position keeping control.

FIG. 7 is a flowchart showing a series of processes to be executed by a watercraft operating controller.

FIG. 8 is a plan view of a watercraft to which marine propulsion devices are mounted according to another example embodiment of the present invention.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

Example embodiments of the present invention will be hereinafter explained with reference to drawings. FIG. 1 is a perspective view of a watercraft 10 including a watercraft operating system 100 according to the example embodiment of the present invention. The watercraft 10 includes a hull 2 and a marine propulsion device 3. More specifically, the watercraft 10 includes a single marine propulsion device 3. In the present example embodiment, the marine propulsion device 3 is an electric outboard motor. The marine propulsion device 3 is attached to the stern of the hull 2 of the watercraft 10. The marine propulsion device 3 is located on the stern in the middle of the watercraft 10 in the right-and-left direction. The marine propulsion device 3 generates a thrust to propel the watercraft 10.

FIG. 2 is a side view of the marine propulsion device 3. The marine propulsion device 3 is attached to the hull 2 through a bracket 11. The marine propulsion device 3 is supported by the bracket 11.

The marine propulsion device 3 includes an upper portion 12, a lower portion 13, a propeller 14, a steering device 15, and an electric motor 16 (see FIG. 3). The upper portion 12 is attached to the bracket 11. The lower portion 13 is disposed below the bracket 11. The lower portion 13 is pivotable about the axis of a steering axle 15a (to be described below) with respect to the upper portion 12. The lower portion 13 includes a case portion 13a and a duct 13b. The case portion 13a is integral with the duct 13b. The duct 13b is disposed below the case portion 13a. The duct 13b has a tubular shape. The propeller 14 is disposed on the duct 13b of the lower portion 13. The propeller 14 generates the thrust when rotated by the driving force of the electric motor 16.

The steering device 15 is configured to pivot the lower portion 13. By pivoting the lower portion 13, the steering device 15 changes the orientation of the thrust generated by the rotation of the propeller 14. The steering device 15 includes the steering axle 15a. The steering axle 15a extends in the up-and-down direction. The steering axle 15a is connected to the upper portion 12 and the duct 13b of the lower portion 13. The steering device 15 includes a motor (not shown in the drawings) to rotate the steering axle 15a about the axis thereof. It should be noted that in the present example embodiment, the lower portion 13 of the marine propulsion device 3 is pivotable in the right-and-left direction within an angular range of about 140 degrees (70 degrees on the right side and 70 degrees on the left side), for example. Because of this, the steering device 15 is configured to pivot the lower portion 13 within the angular range of at least 140 degrees, for example.

The electric motor 16 is driven when supplied with electric power from a battery (not shown in the drawings) disposed in the hull 2. The electric motor 16 includes a stator portion 16a and a rotor portion 16b. The stator portion 16a is fixed to the duct 13b. The stator portion 16a includes a coil (not shown in the drawings). The rotor portion 16b is fixed to the propeller 14. The stator portion 16a is disposed opposite to the rotor portion 16b. The rotor portion 16b includes a plurality of magnets (not shown in the drawings). When the coil of the stator portion 16a is electrified, the propeller 14 is rotated together with the rotor portion 16b.

FIG. 4 is a schematic diagram showing a configuration of the watercraft operating system 100. The marine propulsion device 3 includes a motor controller 17 and a steering controller 18. The motor controller 17 and the steering controller 18 may include control circuits, each of which includes a processor such as a CPU (Central Processing Unit) and memories such as a RAM (Random Access Memory) and a ROM (Read-Only Memory). The motor controller 17 stores programs and data to control the electric motor 16. The motor controller 17 controls the rotational direction and the output of the electric motor 16 in accordance with a command signal outputted thereto from a watercraft operating controller 30 (to be described below).

The steering controller 18 is configured or programmed to control the driving of the steering device 15 in accordance with a command signal outputted thereto from the watercraft operating controller 30. The steering controller 18 stores programs and data to control the steering device 15.

The watercraft operating system 100 includes a steering wheel 24, a remote controller 25, a joystick 26, and a thrust selector 27. The steering wheel 24, the remote controller 25, the joystick 26, and the thrust selector 27 are disposed in a cockpit 10b of the watercraft 10. The cockpit 10b is located farther forward than a center of gravity of the watercraft 10 in the back-and-forth direction. The steering wheel 24, the remote controller 25, the joystick 26, and the thrust selector 27 are manually operable.

The steering wheel 24 enables a vessel operator to manipulate the turning direction of the watercraft 10. The steering wheel 24 includes a sensor 24a. The sensor 24a outputs a steering signal indicating the operating direction and the operating amount of the steering wheel 24.

The remote controller 25 includes a throttle lever 25a. The throttle lever 25a enables the vessel operator to regulate the magnitude of the thrust generated by the marine propulsion device 3. The throttle lever 25a also enables the vessel operator to switch the direction of the thrust generated by the marine propulsion device 3 between a forward moving direction and a rearward moving direction. The throttle lever 25a is operable from a neutral position to a forward moving position and a rearward moving position. The neutral position is an intermediate position between the forward moving position and the rearward moving position. The throttle lever 25a includes a sensor 25b. The sensor 25b outputs a throttle signal indicating the operating direction and the operating amount of the throttle lever 25a.

The joystick 26 is tiltable from the neutral position in the back-and-forth direction and the right-and-left direction (sideways direction). In other words, the joystick 26 is tiltable in all compass directions. The joystick 26 is rotatable about a rotational axis Ax1. In other words, the joystick 26 is operable to twist clockwise and counterclockwise about the rotational axis Ax1. The joystick 26 includes a sensor 26a. The sensor 26a outputs an operating signal according to the operation of the joystick 26. The operating signal contains information regarding the tilt direction and the tilt amount of the joystick 26. The operating signal also contains information regarding the twist direction and the twist amount of the joystick 26. The rudder angle, the magnitude of the output, and the direction of the output of the marine propulsion device 3 are controlled in accordance with the tilt amount and the tilt direction of the joystick 26.

FIG. 5 is a front view of the joystick 26. The joystick 26 includes a joystick button 26b and a position keeping button 31b. The joystick button 26b switches between the following modes: a joystick mode to operate the watercraft 10 using the joystick 26 and a normal mode to operate the watercraft 10 using the remote controller 25 and the steering wheel 24. The position keeping button 31b receives an operation to start the position keeping control and an operation to end the position keeping control.

The thrust selector 27 is provided on the joystick 26. The thrust selector 27 is used in the joystick mode. The thrust selector 27 is operable to select one of a plurality of thrust levels. For example, the thrust selector 27 is able to select one of five-stage thrust levels, including of levels 1 to 5, as the thrust level to operate the watercraft 100 with the joystick 26.

The upper limit of the thrust (maximum thrust) generated by the marine propulsion device 3 increases with an increase in the thrust levels. In other words, the output of the marine propulsion device 3, the magnitude of which depends on the tilt amount of the joystick 26, increases with an increase in the thrust levels.

The thrust selector 27 includes a plus switch 27a and a minus switch 27b. When the plus switch 27a is pressed once, the thrust level at the present stage is increased by one stage. When the minus switch 27b is pressed once, the thrust level at the present stage is reduced by one stage. The thrust selector 27 outputs a setting signal indicating the thrust level selected in accordance with such an operation by the vessel operator as described herein. It should be noted that the thrust selector 27 is not limited to switches, and alternatively, may be a touchscreen or the like.

The watercraft operating system 100 includes the watercraft operating controller 30. The watercraft operating controller 30 includes a processor such as a CPU and memories such as a RAM and a ROM. The watercraft operating controller 30 stores programs and data to control the marine propulsion device 3. The watercraft operating controller 30 is connected to the motor controller 17 and the steering controller 18 through wired or wireless communication. The watercraft operating controller 30 is connected to the steering wheel 24, the remote controller 25, the joystick 26, and the thrust selector 27 through wired or wireless communication.

The watercraft operating controller 30 outputs command signals to the motor controller 17 and the steering controller 18 based on signals outputted thereto from the sensors 24a and 25b. The watercraft operating controller 30 controls the rudder angle, the magnitude of the output, and the direction of the output of the marine propulsion device 3 through the motor controller 17 and the steering controller 18. The watercraft operating controller 30 controls the direction of the output of the marine propulsion device 3 by controlling the rotational direction of the propeller 14.

The watercraft operating controller 30 receives an operating signal outputted thereto from the thrust selector 27. The watercraft operating controller 30 controls the rudder angle, the magnitude of the output, and the direction of the output of the marine propulsion device 3 in accordance with the selected thrust level, the tilt direction of the joystick 26, and the tilt amount of the joystick 26. The watercraft operating controller 30 controls the marine propulsion device 3 to generate a thrust with a magnitude depending on the tilt amount of the joystick 26 (but not exceeding the upper limit to be set based on the selected thrust level) in a direction corresponding to the tilt direction of the joystick 26. The watercraft operating controller 30 increases the output of the marine propulsion device 3, the magnitude of which depends on the tilt amount of the joystick 26, with the increase in thrust levels.

The watercraft operating controller 30 changes the rudder angle of the marine propulsion device 3 such that the watercraft 10 performs bow turning in a direction corresponding to the twist direction of the joystick 26. The watercraft operating controller 30 causes the marine propulsion device 3 to generate a thrust in accordance with the twist amount of the joystick 26.

The watercraft operating controller 30 changes the rudder angle of the marine propulsion device 3 such that the watercraft 10 turns in accordance with operating the joystick 26 to not only tilt forward or rearward but also twist. At this time, the watercraft operating controller 30 causes the marine propulsion device 3 to generate a thrust in accordance with the tilt amount of the joystick 26 and changes the rudder angle of the marine propulsion device 3 such that the watercraft 10 turns in a direction corresponding to the twist direction of the joystick 26.

The watercraft operating system 100 includes a position sensor 31 and a compass sensor 32. The position sensor 31 may be, for instance, a receiver for a GNSS (Global Navigation Satellite System) such as a GPS (Global Positioning System). The position sensor 31 outputs a signal indicating the present position of the watercraft 10. The position sensor 31 is connected to the watercraft operating controller 30 in a communicable manner. The watercraft operating controller 30 obtains the position of the watercraft 10 based on the signal outputted thereto from the position sensor 31.

The compass sensor 32 detects the present compass direction of the watercraft 10. The compass sensor 32 includes, for instance, an IMU (Inertial Measurement Unit). The compass sensor 32 is connected to the watercraft operating controller 30 in a communicable manner.

For example, when receiving an operating signal to be outputted in accordance with an operation of the position keeping button 31b, the watercraft operating controller 30 executes a position keeping control to control the marine propulsion device 3 such that the watercraft 10 is kept at a target spot P0 (see FIG. 6). For example, the target spot P0 is a position where the watercraft 10 has been located at a point in time when the watercraft operating controller 30 received the operating signal from the position keeping button 31b. In the position keeping control, the watercraft operating controller 30 controls the marine propulsion device 3 such that the watercraft 10 is kept at the target spot P0 by directing the bow or stern of the watercraft 10 to the target spot P0 and then moving the watercraft 10 toward the target spot P0. In the position keeping control, the watercraft operating controller 30 causes the watercraft 10 to move toward the target spot P0, for instance, when a distance from a present position P1 of the watercraft 10 to the target spot P0 exceeds a predetermined distance.

In the position keeping control, the watercraft operating controller 30 controls the magnitude of the thrust to be generated by the marine propulsion device 3 in accordance with the amount of displacement of the watercraft 10 from the target spot P0 in the back-and-forth direction. during the position keeping control, the thrust to be generated by the marine propulsion device 3 is controlled to be reduced in magnitude with a reduction in the amount of displacement of the watercraft 10 from the target spot P0 in the back-and-forth direction.

The position keeping control includes a bow turning control to direct the bow or stern of the watercraft 10 to the target spot P0. In the bow turning control, which one of the bow and the stern of the watercraft 10 should be directed to the target spot P0 may be selected by the vessel operator, or alternatively, may be determined by the watercraft operating controller 30 in an automated manner in accordance with a result or results detected by the compass sensor and/or so forth.

The bow turning control includes a first bow turning control and a second bow turning control. In the first bow turning control, based on information regarding the target spot P0 of the watercraft 10 and information regarding the position of the watercraft 10, the output of the marine propulsion device 3 and the rotational direction of the propeller 14 are controlled, while the rudder angle of the marine propulsion device 3 is controlled to be within a predetermined angular range. The predetermined angular range may be, for instance, an angular range of about 80 degrees (about 40 degrees on the right side and about 40 degrees on the left side).

In the second bow turning control, based on the information regarding the target spot P0 of the watercraft 10 and the information regarding the position of the watercraft 10, the rotational direction of the propeller 14 is controlled, while the rudder angle of the marine propulsion device 3 is controlled to be a first angle greater than the maximum angle of the predetermined angular range. FIG. 6 is a diagram schematically showing a series of motions of the watercraft 10 in the second bow turning control. In the second bow turning control, the rudder angle of the marine propulsion device 3 is controlled to be an angle greater than the maximum rudder angle (herein set as 40 degrees, for example) up to which the marine propulsion device 3 is pivotable in the first bow turning control. The first angle may be, for instance, 70 degrees. In the present example embodiment, the first angle is the maximum rudder angle up to which the lower portion 13 of the marine propulsion device 3 is pivotable. In the second bow turning control, the watercraft 10 is able to perform bow turning about the center of gravity thereof substantially on the spot.

Regarding the position keeping control shown in FIG. 6, the watercraft 10 is caused to perform bow turning such that the bow thereof is oriented to the target spot P0 in the second bow turning control. Here, the watercraft operating controller 30 turns the rudder angle rightward by 70 degrees, for example, and controls the rotational direction of the propeller 14 so as to generate a thrust in the rearward moving direction.

The first angle is preferably set to be greater than or equal to about 60 degrees and less than or equal to about 80 degrees, for example. With the first angle being set, while the bow turning of the watercraft 10 is made in the second bow turning control, the operator of the watercraft 10 feels as if the watercraft 10 is bow turning about the cockpit 10b.

The watercraft operating controller 30 executes the second bow turning control when the following predetermined conditions are satisfied in the bow turning control of the position keeping control: a predetermined condition that a difference between a target compass direction of the target spot and a compass direction of the watercraft is greater than or equal to a predetermined value, and a predetermined condition that the output of the marine propulsion device 3 is less than or equal to a predetermined first output. Contrarily, when the predetermined conditions are not satisfied, the watercraft operating controller 30 executes the first bow turning control. The predetermined conditions are satisfied, for instance, when the watercraft is displaced from the target spot by a small amount in the back-and-forth direction such that the thrust required for the bow turning of the watercraft 10 is small in magnitude. It should be noted that, when the predetermined conditions are satisfied during execution of the first bow turning control, the watercraft operating controller 30 executes the second bow turning control instead of executing the first bow turning control.

The predetermined value may be, for instance, 10 degrees. The predetermined first output is set in accordance with, for instance, a thrust to be generated by the marine propulsion device 3 when the watercraft 10 is displaced from the target spot by a small amount in the back-and-forth direction.

In the second bow turning control, the watercraft operating controller 30 controls the output of the marine propulsion device 3 to be a predetermined second output. In the second bow turning control, the watercraft operating controller 30 changes the magnitude of the predetermined second output in accordance with the thrust level selected by the thrust selector 27. In the second bow turning control, the watercraft operating controller 30 increases the magnitude of the predetermined second output with an increase in the thrust levels.

In the second bow turning control, when the rudder angle is changed to be a first angle, the watercraft operating controller 30 stops the output of the marine propulsion device 3 until the rudder angle exceeds a second angle that is greater than a predetermined angular range and is less than the first angle. The second angle may be, for instance, 60 degrees. In other words, in the second bow turning control, when the rudder angle is changed from an angle within the predetermined angular range to the second angle, the watercraft operating controller 30 stops the output of the marine propulsion device 3 until the rudder angle is changed from the angle within the predetermined angular range to the first angle. Accordingly, the marine propulsion device 3 is prevented from generating a thrust in the back-and-forth direction until the rudder angle is changed from the angle within the predetermined angular range to the second angle. Thus, the watercraft 10 is prevented from being displaced in the back-and-forth direction.

FIG. 7 is a flowchart showing a series of processes of the position keeping control to be executed by the watercraft operating controller 30. In step S1, it is determined whether or not the distance from the present position P1 of the watercraft 10 to the target spot P0 exceeds a predetermined value. When it is determined that the distance exceeds the predetermined value, the watercraft operating controller 30 executes a process in step 2.

In step S2, the watercraft operating controller 30 determines whether or not the predetermined conditions described above are satisfied. When it is determined that the predetermined conditions are satisfied, the watercraft operating controller 30 executes the second bow turning control (step S3). When it is determined that the predetermined conditions are not satisfied, the watercraft operating controller 30 executes the first bow turning control (step S6).

In steps S4 and S7, the watercraft operating controller 30 determines whether or not either the bow or stern of the watercraft 10 is oriented to the target spot. In steps S4 and S7, when it is determined that either the bow or stern of the watercraft 10 is oriented to the target spot, the watercraft operating controller 30 causes the watercraft 10 to move toward the target spot in the back-and-forth direction.

In step S4, when it is determined that either the bow or stern of the watercraft 10 is not oriented to the target spot, the watercraft operating controller 30 continues executing the second bow turning control. In step S7, when it is determined that either the bow or stern of the watercraft 10 is not oriented to the target spot, the watercraft operating controller 30 continues executing the first bow turning control. It should be noted that, when the predetermined conditions are satisfied during execution of the first bow turning control, the watercraft operating controller 30 executes the second bow turning control instead of executing the first bow turning control.

In the watercraft operating system 100 according to the present example embodiment explained above, the lower portion 13 is pivotable about the axis of the steering axle 15a with respect to the upper portion 12. Thus, the marine propulsion device 3 is able to have a wider range of rudder angles than, for instance, a type of marine propulsion device in which the lower portion 13 is pivoted together with the upper portion 12. Additionally, in the bow turning control of the position keeping control, the watercraft operating controller 30 executes the second bow turning control to control the rudder angle to be the first angle greater than the maximum rudder angle set in the first bow turning control when the following predetermined conditions are satisfied: a condition that a difference between the target compass direction of the target spot and the compass direction of the watercraft is greater than or equal to the predetermined value, and a condition that the output of the marine propulsion device 3 is less than or equal to the predetermined first output. In the second bow turning control, the watercraft 10 is able to perform bow turning substantially on the spot. Thus, even when the watercraft 10 is displaced from the target spot by a small amount in the back-and-forth direction, the watercraft 10 is able to perform bow turning toward the target spot, while the watercraft 10 is prevented from being greatly displaced in the back-and-forth direction. As a result, in the position keeping control, the watercraft 10 is able to be easily kept at the target spot. Additionally, it is made possible to enhance the accuracy of the position keeping control.

Example embodiments of the present invention have been explained above. However, the present invention is not limited to the example embodiments described above and a variety of changes can be made without departing from the gist of the present invention.

As shown in FIG. 8, the watercraft operating system 100 may further include a primary propulsion device 40. The primary propulsion device 40 may be an outboard motor including an internal combustion engine, or alternatively, an electric outboard motor. The primary propulsion device 40 is disposed on the stern in the middle of the watercraft 10 in the right-and-left direction. In this case, the marine propulsion device 3 may function as an auxiliary propulsion device disposed on the stern toward one side of the watercraft 10 in the right-and-left direction.

The pivotable range of the lower portion 13 of the marine propulsion device 3 is not limited to that described in the example embodiments described above. For example, the lower portion 13 may be pivotable in the right-and-left direction within an angular range of about 180 degrees (about 90 degrees on the right side and about 90 degrees on the left side) or an angular range of about 120 degrees (about 60 degrees on the right side and about 60 degrees on the left side.

While example embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.