This is a library for processing encoder
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ENCODER_PROCESSOR.cpp
00001 /** 00002 * Note: This is a cross-platform version which is separated from hardware. 00003 * --------------------------------------------------------------------------- 00004 * This module is modified by Chun-Feng Huang for abstracting and more functionality. 00005 * Modified by: Chun-Feng Huang 00006 * E-mail: bens0516@gmail.com 00007 * 00008 */ 00009 00010 //----------------------------------// 00011 /** 00012 * @author Aaron Berk 00013 * 00014 * @section LICENSE 00015 * 00016 * Copyright (c) 2010 ARM Limited 00017 * 00018 * Permission is hereby granted, free of charge, to any person obtaining a copy 00019 * of this software and associated documentation files (the "Software"), to deal 00020 * in the Software without restriction, including without limitation the rights 00021 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 00022 * copies of the Software, and to permit persons to whom the Software is 00023 * furnished to do so, subject to the following conditions: 00024 * 00025 * The above copyright notice and this permission notice shall be included in 00026 * all copies or substantial portions of the Software. 00027 * 00028 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 00029 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 00030 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 00031 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 00032 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 00033 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 00034 * THE SOFTWARE. 00035 * 00036 * @section DESCRIPTION 00037 * 00038 * Quadrature Encoder Interface. 00039 * 00040 * A quadrature encoder consists of two code tracks on a disc which are 90 00041 * degrees out of phase. It can be used to determine how far a wheel has 00042 * rotated, relative to a known starting position. 00043 * 00044 * Only one code track changes at a time leading to a more robust system than 00045 * a single track, because any jitter around any edge won't cause a state 00046 * change as the other track will remain constant. 00047 * 00048 * Encoders can be a homebrew affair, consisting of infrared emitters/receivers 00049 * and paper code tracks consisting of alternating black and white sections; 00050 * alternatively, complete disk and PCB emitter/receiver encoder systems can 00051 * be bought, but the interface, regardless of implementation is the same. 00052 * 00053 * +-----+ +-----+ +-----+ 00054 * Channel A | ^ | | | | | 00055 * ---+ ^ +-----+ +-----+ +----- 00056 * ^ ^ 00057 * ^ +-----+ +-----+ +-----+ 00058 * Channel B ^ | | | | | | 00059 * ------+ +-----+ +-----+ +----- 00060 * ^ ^ 00061 * ^ ^ 00062 * 90deg 00063 * 00064 * The interface uses X2 encoding by default which calculates the pulse count 00065 * based on reading the current state after each rising and falling edge of 00066 * channel A. 00067 * 00068 * +-----+ +-----+ +-----+ 00069 * Channel A | | | | | | 00070 * ---+ +-----+ +-----+ +----- 00071 * ^ ^ ^ ^ ^ 00072 * ^ +-----+ ^ +-----+ ^ +-----+ 00073 * Channel B ^ | ^ | ^ | ^ | ^ | | 00074 * ------+ ^ +-----+ ^ +-----+ +-- 00075 * ^ ^ ^ ^ ^ 00076 * ^ ^ ^ ^ ^ 00077 * Pulse count 0 1 2 3 4 5 ... 00078 * 00079 * This interface can also use X4 encoding which calculates the pulse count 00080 * based on reading the current state after each rising and falling edge of 00081 * either channel. 00082 * 00083 * +-----+ +-----+ +-----+ 00084 * Channel A | | | | | | 00085 * ---+ +-----+ +-----+ +----- 00086 * ^ ^ ^ ^ ^ 00087 * ^ +-----+ ^ +-----+ ^ +-----+ 00088 * Channel B ^ | ^ | ^ | ^ | ^ | | 00089 * ------+ ^ +-----+ ^ +-----+ +-- 00090 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 00091 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 00092 * Pulse count 0 1 2 3 4 5 6 7 8 9 ... 00093 * 00094 * It defaults 00095 * 00096 * An optional index channel can be used which determines when a full 00097 * revolution has occured. 00098 * 00099 * If a 4 pules per revolution encoder was used, with X4 encoding, 00100 * the following would be observed. 00101 * 00102 * +-----+ +-----+ +-----+ 00103 * Channel A | | | | | | 00104 * ---+ +-----+ +-----+ +----- 00105 * ^ ^ ^ ^ ^ 00106 * ^ +-----+ ^ +-----+ ^ +-----+ 00107 * Channel B ^ | ^ | ^ | ^ | ^ | | 00108 * ------+ ^ +-----+ ^ +-----+ +-- 00109 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 00110 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 00111 * ^ ^ ^ +--+ ^ ^ +--+ ^ 00112 * ^ ^ ^ | | ^ ^ | | ^ 00113 * Index ------------+ +--------+ +----------- 00114 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 00115 * Pulse count 0 1 2 3 4 5 6 7 8 9 ... 00116 * Rev. count 0 1 2 00117 * 00118 * Rotational position in degrees can be calculated by: 00119 * 00120 * (pulse count / X * N) * 360 00121 * 00122 * Where X is the encoding type [e.g. X4 encoding => X=4], and N is the number 00123 * of pulses per revolution. 00124 * 00125 * Linear position can be calculated by: 00126 * 00127 * (pulse count / X * N) * (1 / PPI) 00128 * 00129 * Where X is encoding type [e.g. X4 encoding => X=44], N is the number of 00130 * pulses per revolution, and PPI is pulses per inch, or the equivalent for 00131 * any other unit of displacement. PPI can be calculated by taking the 00132 * circumference of the wheel or encoder disk and dividing it by the number 00133 * of pulses per revolution. 00134 */ 00135 00136 /** 00137 * Includes 00138 */ 00139 #include "ENCODER_PROCESSOR.h" 00140 00141 ENCODER_PROCESSOR::ENCODER_PROCESSOR(int pulsesPerRevolution_in, int size_MA_window_in, double sampling_time_in, Encoding encoding): 00142 pulsesPerRevolution(pulsesPerRevolution_in), size_MA_window(size_MA_window_in), Ts(sampling_time_in) 00143 { 00144 // 00145 is_initiated = false; 00146 00147 00148 // 00149 MA_window.assign(size_MA_window, 0); 00150 00151 delta_count = 0; 00152 idx_MA_array = 0; 00153 00154 00155 pulses_ = 0; 00156 revolutions_ = 0; 00157 encoding_ = encoding; 00158 00159 // Findout what the current state is. 00160 // int chanA = channelA_.read(); 00161 // int chanB = channelB_.read(); 00162 00163 //2-bit state. 00164 encoderState_now = 0; // (chanA << 1) | (chanB); 00165 encoderState_pre = encoderState_now; 00166 00167 // Attaching call back function 00168 //X2 encoding uses interrupts on only channel A. 00169 //X4 encoding uses interrupts on channel A and on channel B. 00170 00171 00172 // Unit transformation 00173 // Rotational speed 00174 count_2_rad_s = 1.0/(pulsesPerRevolution*1.0)*6.2831852/Ts/(size_MA_window*1.0); 00175 count_2_deg_s = 1.0/(pulsesPerRevolution*1.0)*360.0/Ts/(size_MA_window*1.0); 00176 // Angle 00177 count_2_rad = 1.0/(pulsesPerRevolution*1.0)*6.2831852; 00178 count_2_deg = 1.0/(pulsesPerRevolution*1.0)*360.0; 00179 } 00180 00181 // Process control 00182 void ENCODER_PROCESSOR::reset(void) { 00183 00184 pulses_ = 0; 00185 revolutions_ = 0; 00186 00187 } 00188 00189 // Encode (call Back) 00190 ///////////////////////// 00191 // +-------------+ 00192 // | X2 Encoding | 00193 // +-------------+ 00194 // 00195 // When observing states two patterns will appear: 00196 // 00197 // Counter clockwise rotation: 00198 // 00199 // 10 -> 01 -> 10 -> 01 -> ... 00200 // 00201 // Clockwise rotation: 00202 // 00203 // 11 -> 00 -> 11 -> 00 -> ... 00204 // 00205 // We consider counter clockwise rotation to be "forward" and 00206 // counter clockwise to be "backward". Therefore pulse count will increase 00207 // during counter clockwise rotation and decrease during clockwise rotation. 00208 // 00209 // +-------------+ 00210 // | X4 Encoding | 00211 // +-------------+ 00212 // 00213 // There are four possible states for a quadrature encoder which correspond to 00214 // 2-bit gray code. 00215 // 00216 // A state change is only valid if of only one bit has changed. 00217 // A state change is invalid if both bits have changed. 00218 // 00219 // Clockwise Rotation -> 00220 // (The bits are constructed as "AB") 00221 // 00 01 11 10 00 00222 // 00223 // <- Counter Clockwise Rotation 00224 // 00225 // If we observe any valid state changes going from left to right, we have 00226 // moved one pulse clockwise [we will consider this "backward" or "negative"]. 00227 // 00228 // If we observe any valid state changes going from right to left we have 00229 // moved one pulse counter clockwise [we will consider this "forward" or 00230 // "positive"]. 00231 // 00232 // We might enter an invalid state for a number of reasons which are hard to 00233 // predict - if this is the case, it is generally safe to ignore it, update 00234 // the state and carry on, with the error correcting itself shortly after. 00235 00236 00237 //---------------------------------------------// 00238 // Call-back function for both pin A and pin B interupt (rise and fall) 00239 void ENCODER_PROCESSOR::IntrCB_pulseUpdate(int phase_A, int phase_B) { 00240 00241 if (!is_initiated){ 00242 //2-bit state. 00243 encoderState_now = (phase_A << 1) | (phase_B); // AB 00244 encoderState_pre = encoderState_now; 00245 // 00246 is_initiated = true; 00247 // 00248 return; 00249 } 00250 00251 //--------------------------------// 00252 int change = 0; 00253 00254 //2-bit state. 00255 encoderState_now = (phase_A << 1) | (phase_B); // AB 00256 00257 if (encoding_ == X2_ENCODING) { 00258 00259 //11->00->11->00 is counter clockwise rotation or "forward". 00260 if ((encoderState_pre == 0x3 && encoderState_now == 0x0) || 00261 (encoderState_pre == 0x0 && encoderState_now == 0x3)) { 00262 00263 pulses_++; 00264 00265 } 00266 //10->01->10->01 is clockwise rotation or "backward". 00267 else if ((encoderState_pre == 0x2 && encoderState_now == 0x1) || 00268 (encoderState_pre == 0x1 && encoderState_now == 0x2)) { 00269 00270 pulses_--; 00271 00272 } 00273 00274 } else{ // if (encoding_ == X4_ENCODING) { 00275 00276 //Entered a new valid state. 00277 if (((encoderState_now ^ encoderState_pre) != INVALID) && (encoderState_now != encoderState_pre)) { 00278 // 2 bit state. 00279 // (Right hand bit of prev) XOR (left hand bit of current) 00280 // B_(n-1) xor A_n (because of the 90deg phase shift and A is leading B when rotates clockwise) 00281 // gives 0 if clockwise rotation and 1 if counter clockwise rotation. 00282 change = (encoderState_pre & PREV_MASK) ^ ((encoderState_now & CURR_MASK) >> 1); 00283 00284 if (change == 0) { 00285 change = -1; 00286 } 00287 00288 pulses_ -= change; 00289 } 00290 00291 } 00292 00293 encoderState_pre = encoderState_now; 00294 00295 } 00296 // (Un-necessary) Call-back function for index-pin interupt 00297 void ENCODER_PROCESSOR::IntrCB_indexUpdate(void) { 00298 revolutions_++; 00299 } 00300 //---------------------------------------------// 00301 00302 00303 00304 //---------------------------------------------// 00305 // Iterate at each timer interupt 00306 void ENCODER_PROCESSOR::iterateOnce(){ // Moving average: calculating the speed of the motor for feedback control 00307 // new input 00308 MA_window[idx_MA_array] = pulses_; 00309 00310 // idx_next: Actually, it is the oldest one. 00311 size_t idx_next = idx_MA_array + 1; 00312 if(idx_next > (size_MA_window - 1) ){idx_next = 0;} 00313 // Calculate the total number of pulses within the period 00314 delta_count = (MA_window[idx_MA_array] - MA_window[idx_next]); 00315 // 00316 idx_MA_array ++; 00317 if(idx_MA_array > (size_MA_window -1) ){idx_MA_array = 0;} 00318 } 00319 //---------------------------------------------// 00320 00321 00322 // Get states 00323 int ENCODER_PROCESSOR::getEncoderState(void) { 00324 return encoderState_now; 00325 } 00326 00327 int ENCODER_PROCESSOR::getPulses(void) { 00328 return pulses_; 00329 } 00330 00331 int ENCODER_PROCESSOR::getRevolutions(void) { 00332 return revolutions_; 00333 } 00334 00335 // Get results 00336 // Rotational speed 00337 double ENCODER_PROCESSOR::getAngularSpeed(){ 00338 return delta_count*count_2_rad_s; 00339 } 00340 00341 double ENCODER_PROCESSOR::getAngularSpeed_deg_s(){ 00342 return delta_count*count_2_deg_s; 00343 } 00344 // Angle 00345 double ENCODER_PROCESSOR::getAngle(bool is_ranged){ // rad, if is_ranged, return 0~2*PI 00346 // 00347 int pulse_temp = this->pulses_; 00348 // 00349 if (is_ranged){ 00350 revolutions_ = pulse_temp/pulsesPerRevolution; 00351 return (pulse_temp % pulsesPerRevolution)*count_2_rad; 00352 }else{ 00353 return (pulse_temp*count_2_rad); 00354 } 00355 } 00356 double ENCODER_PROCESSOR::getAngle_deg(bool is_ranged){ // deg, if is_ranged, return 0~360 00357 // 00358 int pulse_temp = this->pulses_; 00359 // 00360 if (is_ranged){ 00361 revolutions_ = pulse_temp/pulsesPerRevolution; 00362 return (pulse_temp % pulsesPerRevolution)*count_2_deg; 00363 }else{ 00364 return (pulse_temp*count_2_deg); 00365 } 00366 }
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