Dual input servo coupled control sticks

Details Dual input servo coupled control sticks Dual input servo coupled control sticks

2001-03-22

2002-10-01

Dang, Khanh (Department: 2832)

Electricity: motive power systems

Positional servo systems

With compensating features

C318S618000, C244S191000, C244S07600R, C244S223000

Reexamination Certificate

active

06459228

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an active control system for providing desired force versus displacement characteristics to a pair of manual input devices such as the flight control sticks operated by a pilot and co-pilot flying an aircraft. In addition to providing a desired force versus displacement profile for the input devices, the active control system further acts to reflect manual inputs applied at one of the input devices at the other of the two input devices. Additionally, inputs from an outside source, such as an autopilot signal, can be used to reflect motion onto both control sticks. Variable gain velocity damping is also provided to reduce oscillations at or near a zero or null position.
In many applications it is desirable to impart tactile feedback to users of manually operated input devices. For example, in mechanically linked systems, tactile feedback to the operator is provided as a result of the force required to move the mechanical parts associated with the system. In electronically controlled systems, however, the physical interrelationship between the input device and the mechanical components acted upon is replaced by electrical signals generated by sensors in the input device which signal actuators to act on the mechanical components. In such systems, the force versus displacement characteristics of the input device have no direct relationship to the systems being controlled. It is thus desirable to generate mechanical forces to be applied to the input device to emulate mechanically linked systems. Such emulation provides the operator with tactile feedback regarding the state of the system and the effects of his or her input actions. Heretofore, self-centering control sticks having force versus displacement characteristics that emulate mechanical systems have employed mechanical spring arrangements or active servo control systems.
Aircraft flight control systems are an application where it is particularly important to provide accurate tactile feedback to the pilot or co-pilot operating a control stick or yoke which electrically interfaces with the mechanical systems for controlling the flight control surfaces of the aircraft. Such “fly by wire” systems employ various sensors to determine the position of and/or force applied to the control stick in order to translate the pilot's input commands into electrical signals for controlling the flight control surfaces of the aircraft. In many aircraft, dual control sticks are provided, one to be operated by the pilot and a second to be operated by a co-pilot. In cases where there are dual control sticks, it is desirable that actions taken on either one of the control sticks are reflected in the other control stick in the form of a force supplied to the second control stick in the direction of the action taken on the first control stick.
An active control system for providing variable force feel characteristics to a pair of manual input control stick is disclosed in U.S. Pat. No. 5,291,113 to Hegg et al. According to the system disclosed there, a desired force versus displacement profile is provided in which the magnitude of the control stick displacement is proportional to the force applied in order to emulate a purely mechanically linked system. The system includes a pair of control sticks each of which is directly coupled through a gimble to a motor in a conventional manner. A position signal from the first input device is fed back and combined with an autopilot or center position signal to create an error signal. This error signal is amplified and input to servo control electronics to generate excitation currents for a motor coupled to the control stick. Thus, this position feedback loop causes the motor to drive the control stick in a direction to reduce the amount of error between the position commanded by the autopilot signal and the actual position of the control stick. The gain of the amplifier that acts on the difference between the stick position and the autopilot reference command in Hegg, et al. is fixed, and serves to define the mechanical spring rate being emulated, resulting in a single force-versus-displacement gradient profile.
A second position signal generated from the position of the second control stick is also fed back and summed with the position signal from the first control stick. This signal is also amplified and summed with the error signal input to the servo controller driving the motor coupled to the first control stick. The signal representing the combined position signal from the first and second control sticks is amplified to a far greater extent than the error signal between the autopilot signal in the position of the first control stick. Thus, the position error signal between the first and second control sticks will dominate over the position error signal between the autopilot signal and the first control sticks. The motor coupled to the first control stick will drive the first control stick to a position intended to eliminate the position error between the first and second control sticks, as well as attempting to reconcile the position between the first control stick and the position commanded by the autopilot signal, with elimination of the position error between the two control sticks predominating.
The position signals from both the first and second control sticks are also in fed into the servo control electronics driving the motor coupled to the second control stick. Thus, displacement of the first control stick will also be reflected back to the second control stick. Discrepancies between the autopilot signal and the second control stick are rectified by having the second control stick follow the position of the first control stick. The operational characteristics of such a system are poor since the system relies on the reconciled position of one stick as the signal to drive the other. This can cause poor frequency response, lag in position tracking, poor coupling and poor feel.
A second embodiment disclosed by Hegg et al. further describes a torque sensor for generating a signal representative of the torque applied to the first and second control sticks. These signals are fed back and summed with the position error signals which are input to the servo control electronics driving the motors which are coupled to the first and second control sticks.
Another example of an active control system for controlling the force feel characteristics of a manual input device such as a flight control stick is disclosed in U.S. Pat. No. 5,347,204 Gregory et al. A system is disclosed there for providing variable damping to a servo control system in order to prevent oscillations due to motor torque and high gain characteristics at or near the center position. A signal representing the angular velocity of the control stick is combined with the position error signal which is supplied to the servo control electronics driving the motor coupled to the control stick. The velocity feedback signal is subjected to position dependent scaling which provides a variable rate gain which is dependent on the angular position of the control stick. The position dependent scaling is implemented via an amplifier inserted in the velocity feedback loop. The gain of the amplifier is established by a pair of resistors connected in parallel between one of the inputs and the output of the amplifier. A position dependent switch is connected in series with one of the resistors such that when the control sticks is positioned within a first position range the switch is open, and the gain of the amplifier is determined by only one of the resistors connected across the input and output of the amplifier. When the control stick is in a second position range, the switch is closed and the gain of the amplifier is determined by the parallel combination of the two resistors. Thus, a higher gain setting for the feedback amplifier may be established when the control stick is near the zero position to provide higher rate damping for the overall servo loop when the control stick is near the zero

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