Overview
Electronics will play a major role in the control of marine drives. As already accepted in the aircraft industry, the techniques of digital computers, electronics, and network communications will make vessel control systems cheaper to build, install, and maintain. Further these electronics systems allow intelligent methods of control. Vessels so equipped will be far easier to operate. They will perform both precise and radical maneuvers safely.
The steering systems I am developing use proven electronics and mathematical control theories used in both civil and military applications. It does this in an economical way applicable to both commercial and consumer products.
Current jet as well as conventional marine drives use hydraulic systems. Pumps connected to power units supply flow of hydraulic fluid for steering and control actuators. Control valves are used to direct fluid flow rate and direction through lines leading from a control valve such as as a helm steering wheel though the vessel to the hydraulic pumps, coolers and steering actuators. Transmission controls and engine throttles can also work similarly. While these systems are generally simple in theory, in practice they lack "intelligence". They can not take into account any factors other than the operator's direct steering, throttle amount and clutch commands. They can not limit control authority of steering at high vessel speeds for safety reasons, provide vessel position keeping, autopilot functions, or nozzle controls on jets to simulate conventional outdrive systems when reversing. Long, bulky and expensive hydraulic lines are required everywhere.
Electronics can provide an effective alternative to direct hydraulic controls. Electronic proportional control valves can be inserted into this system close to the actuators that turn and control the vessel. A proportional control valve is a device that controls the flow of hydraulic fluid according to the amount of electrical current supplied to its inputs. Transistor drive circuits connected to local computer processors can intelligently command these proportional hydraulic valves. Replacing the mechanical and hydraulic lines are light, inexpensive, free topology networks. As in an office environment multiple electronic computer devices are interconnected though out the ship to share computing power, sensor information, operators interfaces and actuators. Electrical wiring is minimal. Additional network nodes can be placed anywhere to add sensors, actuators, operator controls or computer displays. Because the boat's controls are indirectly ran through a computer many enhanced operations are possible including:
- Automatic limitations on a drive's angle left or right based on power settings and boat speed.
- Position keeping.
- Automatic pilot functions.
- Enhanced docking maneuverability.
- Non-conventional operator controls such as multiaxis joysticks.
These features are impossible or impractical without an electronic control system. For reasons of marketability and product liability they are required.
Design Elements
The steering control system has been designed for networked electronic helm control from any remote locations. The system incorporates the basics of computing power to allow steering from wheel or joystick inputs. It incorporates the building blocks to allow all the aforementioned enhancements. This system includes these components: (See figure 1)
- Engine mounted hydraulic pump to supply mechanical system power.
- Hydraulic fluid cooler.
- Hydraulic pressure regulator to maintain a constant pressure regardless of engine RPM.
- 4 Way Hydraulic proportional control valve to allow electrical control of the fluid delivered to a hydraulic motor thus controlling torque applied to the steering.
- Hydraulic actuator connected to the steering.
- An encoder that returns a digital representation of the angle that the steering is pointed and any instant.
- An electronic control module attached to or near the hydraulic steering actuator and encoder.
The electronic control module is built to withstand the marine environment for temperature, humidity, salt and vibration. It is quite small in size and contains:
- A microcontroller to process commands and perform mathematical calculations.
- An electrical interface between the microcontroller and the feedback optical encoder.
- Smart power transistors to drive the proportional control valve.
- Electronics for an approved mission critical "fly-by-wire" network interface.
- A local power system power supply for the control electronics.
At the helm another module accepts input from power levers, steering wheels and joysticks, process these pieces of information and transmit commands to the steering control via the network connection. This module has the same environmental considerations as the steering control. It includes:
- A microcontroller to issue commands and accept user inputs from optical wheel position encoders or variable resistors.
- An electrical interface as in the steering controller to accept either optical encoder data from a steering wheel or joystick.
- Electronics for the "fly-by-wire" network interface.
- A local switching power system power supply for the control electronics.
A simple system consists of two electronic self contained modules, simple network and power wires, a steering input device and the hydraulic components on the drive and engine. All the assemblies are made with off the self components used in commercial industries. They are readably available and very cost effective. From a software standpoint the system is designed for field upgradability via the control network. This gives much greater flexibility in future enhancements and system repairs.
Current Design Status
Conceptual and prototype design has be completed for this steering system. A network has been selected with its associated electronics and development equipment obtained. A hydraulic proportional control valve has been selected. An optical encoder has been selected for incorporation onto the steering unit. The electrical design for the power transistors, and the optical encoder interface to a microcontroller has been completed. The control equations have been defined and verified. They are based on industry standard PID (Proportional, Integral, Differential) algorithms. The electronics at the steering wheel/joystick end are somewhat simpler and contain only a subset of the electronics needed in the steering controller.
To be completed for a functional prototype:
- Software coding implementing the control algorithm.
- Hardware design of the helm station.
- Software coding of the steering helm station.
- DC to DC power supply design or selection.
- Printed circuit board layout and assembly.
- Mechanical packaging of all the modules and sensors.
- Measurement and verification of system control forces and response times.
Upon completion of a functional prototype and software the entire system will need to be repackaged in a form conducive to production. Production units will have to allow ease of assembly, testing, repair, and be able to take physical abuses in daily use. These pre-production units will then need a period of beta testing at customer sites to verify that all components meet our goals of reliability and performance. It is estimated that there is 3 to 6 man months of work in the design phase yet to be completed for a commercial system. Another 3 months production packaging and beta testing.
Summary
This control system is general purpose and can be used in many different configurations of drives, boats, and number of and drive sizes. The same units can be used for jet and conventional drive systems. The system is designed to be extendable. Larger and larger networks of computers, GPSs, communications, sounders, radars, and user displays can be integrated. The units use a network that is specified for use by the U.S. Navy and is approved for use in aircraft control systems by the FAA. These two steering components will only be the first of an extensive line of sensor and control products.
