111 lines
5.0 KiB
Matlab
111 lines
5.0 KiB
Matlab
classdef AHRS < handle
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%% Public properties
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properties (Access = public)
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SamplePeriod = 1/256;
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Quaternion = [1 0 0 0]; % output quaternion describing the sensor relative to the Earth
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Kp = 2; % proportional gain
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Ki = 0; % integral gain
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KpInit = 200; % proportional gain used during initialisation
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InitPeriod = 5; % initialisation period in seconds
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end
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%% Private properties
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properties (Access = private)
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q = [1 0 0 0]; % internal quaternion describing the Earth relative to the sensor
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IntError = [0 0 0]'; % integral error
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KpRamped; % internal proportional gain used to ramp during initialisation
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end
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%% Public methods
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methods (Access = public)
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function obj = AHRS(varargin)
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for i = 1:2:nargin
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if strcmp(varargin{i}, 'SamplePeriod'), obj.SamplePeriod = varargin{i+1};
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elseif strcmp(varargin{i}, 'Quaternion')
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obj.Quaternion = varargin{i+1};
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obj.q = quaternConj(obj.Quaternion);
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elseif strcmp(varargin{i}, 'Kp'), obj.Kp = varargin{i+1};
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elseif strcmp(varargin{i}, 'Ki'), obj.Ki = varargin{i+1};
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elseif strcmp(varargin{i}, 'KpInit'), obj.KpInit = varargin{i+1};
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elseif strcmp(varargin{i}, 'InitPeriod'), obj.InitPeriod = varargin{i+1};
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else error('Invalid argument');
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end
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obj.KpRamped = obj.KpInit;
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end;
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end
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function obj = Update(obj, Gyroscope, Accelerometer, Magnetometer)
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error('This method is unimplemented');
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end
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function obj = UpdateIMU(obj, Gyroscope, Accelerometer)
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% Normalise accelerometer measurement
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if(norm(Accelerometer) == 0) % handle NaN
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warning(0, 'Accelerometer magnitude is zero. Algorithm update aborted.');
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return;
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else
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Accelerometer = Accelerometer / norm(Accelerometer); % normalise measurement
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end
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% Compute error between estimated and measured direction of gravity
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v = [2*(obj.q(2)*obj.q(4) - obj.q(1)*obj.q(3))
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2*(obj.q(1)*obj.q(2) + obj.q(3)*obj.q(4))
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obj.q(1)^2 - obj.q(2)^2 - obj.q(3)^2 + obj.q(4)^2]; % estimated direction of gravity
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error = cross(v, Accelerometer');
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% % Compute ramped Kp value used during init period
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% if(obj.KpRamped > obj.Kp)
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% obj.IntError = [0 0 0]';
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% obj.KpRamped = obj.KpRamped - (obj.KpInit - obj.Kp) / (obj.InitPeriod / obj.SamplePeriod);
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% else % init period complete
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% obj.KpRamped = obj.Kp;
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obj.IntError = obj.IntError + error; % compute integral feedback terms (only outside of init period)
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% end
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% Apply feedback terms
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Ref = Gyroscope - (obj.Kp*error + obj.Ki*obj.IntError)';
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% Compute rate of change of quaternion
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pDot = 0.5 * obj.quaternProd(obj.q, [0 Ref(1) Ref(2) Ref(3)]); % compute rate of change of quaternion
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obj.q = obj.q + pDot * obj.SamplePeriod; % integrate rate of change of quaternion
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obj.q = obj.q / norm(obj.q); % normalise quaternion
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% Store conjugate
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obj.Quaternion = obj.quaternConj(obj.q);
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end
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function obj = Reset(obj)
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obj.KpRamped = obj.KpInit; % start Kp ramp-down
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obj.IntError = [0 0 0]'; % reset integral terms
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obj.q = [1 0 0 0]; % set quaternion to alignment
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end
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% function obj = StepDownKp(obj, Kp)
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% obj.KpRamped = Kp;
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% obj.Kp = Kp;
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% end
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end
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%% Get/set methods
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methods
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function obj = set.Quaternion(obj, value)
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if(norm(value) == 0)
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error('Quaternion magnitude cannot be zero.');
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end
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value = value / norm(value);
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obj.Quaternion = value;
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obj.q = obj.quaternConj(value);
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end
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end
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%% Private methods
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methods (Access = private)
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function ab = quaternProd(obj, a, b)
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ab(:,1) = a(:,1).*b(:,1)-a(:,2).*b(:,2)-a(:,3).*b(:,3)-a(:,4).*b(:,4);
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ab(:,2) = a(:,1).*b(:,2)+a(:,2).*b(:,1)+a(:,3).*b(:,4)-a(:,4).*b(:,3);
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ab(:,3) = a(:,1).*b(:,3)-a(:,2).*b(:,4)+a(:,3).*b(:,1)+a(:,4).*b(:,2);
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ab(:,4) = a(:,1).*b(:,4)+a(:,2).*b(:,3)-a(:,3).*b(:,2)+a(:,4).*b(:,1);
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end
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function qConj = quaternConj(obj, q)
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qConj = [q(:,1) -q(:,2) -q(:,3) -q(:,4)];
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end
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end
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end |