Block Diagram of an Automatic Steering System with Auto-Pilot and Valve Operated Steering Gear
An automatic steering system, also known as autopilot, utilizes various components to maintain a set course for a vessel. Here’s a block diagram outlining its operation:
Blocks:
- Course Reference System (CRS):
- This block provides a reference for the desired course. It can be a:
- Gyrocompass: Senses the vessel’s heading based on Earth’s rotation.
- GPS (Global Positioning System): Provides highly accurate position information.
- Combination of both: For enhanced accuracy and redundancy.
- This block provides a reference for the desired course. It can be a:
- Course Setter:
- This allows the operator to input the desired course (heading) for the autopilot to follow.
- Heading Sensor:
- Senses the vessel’s actual heading information. This can be:
- Gyrocompass output (if separate from CRS).
- GPS derived heading: Utilizing position data and course over ground (COG).
- Senses the vessel’s actual heading information. This can be:
- Autopilot Controller:
- This is the “brain” of the system. It compares the desired course (from CRS and Course Setter) with the actual heading (from Heading Sensor).
- Based on the difference (course error), the controller calculates the necessary rudder adjustments to minimize the error and maintain the desired course.
- Common control algorithms used include Proportional-Integral-Derivative (PID) control.
- Rudder Command Signal:
- The autopilot controller generates a control signal based on the calculated rudder adjustment. This signal can be:
- Electrical signal: Sent to a servo motor driving a valve.
- Hydraulic signal: Controls a pilot valve in a hydraulic system.
- The autopilot controller generates a control signal based on the calculated rudder adjustment. This signal can be:
- Valve Operated Steering Gear:
- This block translates the control signal from the autopilot into physical movement of the rudder. It can be:
- Electro-hydraulic system: An electric motor drives a pump that pressurizes hydraulic fluid. A servo valve, controlled by the autopilot’s signal, directs the fluid flow to rams that move the rudder.
- Electro-pneumatic system: A solenoid valve, controlled by the autopilot’s electrical signal, directs compressed air to actuators that move the rudder.
- This block translates the control signal from the autopilot into physical movement of the rudder. It can be:
- Feedback Loop:
- The actual rudder position (often sensed by a rudder angle sensor) can be fed back to the autopilot controller. This feedback helps to ensure accurate and precise rudder adjustments.
Overall Operation:
- The operator sets the desired course using the Course Setter.
- The CRS and Heading Sensor provide continuous information about the desired and actual headings, respectively.
- The autopilot controller compares these headings and calculates the course error.
- Based on the error, the controller generates a rudder command signal.
- The valve-operated steering gear translates this signal into rudder movement.
- (Optional) The actual rudder position is fed back to the controller for improved accuracy.
This continuous cycle of comparison, calculation, and adjustment allows the autopilot to maintain the set course automatically, reducing workload for the crew and improving navigational efficiency.