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Dependencies:   mbed FastIO FastPWM USBDevice

Plunger/rotarySensor.h@102:41d49e78c253, 2019-12-02 (annotated)

Committer:
mjr
Date:
Mon Dec 02 02:01:30 2019 +0000
Revision:
102:41d49e78c253
Parent:
100:1ff35c07217c
Child:
103:dec22cd65b2a
AEAT-6012 plunger sensor now working

Who changed what in which revision?

UserRevisionLine numberNew contents of line
mjr 100:1ff35c07217c 1 // Plunger sensor implementation for rotary absolute encoders
mjr 100:1ff35c07217c 2 //
mjr 100:1ff35c07217c 3 // This implements the plunger interfaces for rotary absolute encoders. A
mjr 100:1ff35c07217c 4 // rotary encoder measures the angle of a rotating shaft. For plunger sensing,
mjr 100:1ff35c07217c 5 // we can convert the plunger's linear motion into angular motion using a
mjr 100:1ff35c07217c 6 // mechanical linkage between the plunger rod and a rotating shaft positioned
mjr 100:1ff35c07217c 7 // at a fixed point, somewhere nearby, but off of the plunger's axis:
mjr 100:1ff35c07217c 8 //
mjr 100:1ff35c07217c 9 // =X=======================|=== <- plunger, X = connector attachment point
mjr 100:1ff35c07217c 10 // \
mjr 100:1ff35c07217c 11 // \ <- connector between plunger and shaft
mjr 100:1ff35c07217c 12 // \
mjr 100:1ff35c07217c 13 // * <- rotating shaft, at a fixed position
mjr 100:1ff35c07217c 14 //
mjr 100:1ff35c07217c 15 // As the plunger moves, the angle of the connector relative to the fixed
mjr 100:1ff35c07217c 16 // shaft position changes in a predictable way, so by measuring the rotational
mjr 100:1ff35c07217c 17 // position of the shaft at any given time, we can infer the plunger's
mjr 100:1ff35c07217c 18 // linear position.
mjr 100:1ff35c07217c 19 //
mjr 100:1ff35c07217c 20 // (Note that the mechanical diagram is simplified for ASCII art purposes.
mjr 100:1ff35c07217c 21 // What's not shown is that the distance between the rotating shaft and the
mjr 100:1ff35c07217c 22 // "X" connection point on the plunger varies as the plunger moves, so the
mjr 100:1ff35c07217c 23 // mechanical linkage requires some way to accommodate that changing length.
mjr 100:1ff35c07217c 24 // One way is to use a spring as the linkage; another is to use a rigid
mjr 100:1ff35c07217c 25 // connector with a sliding coupling at one or the other end. We leave
mjr 100:1ff35c07217c 26 // these details up to the mechanical design; the software isn't affected
mjr 100:1ff35c07217c 27 // as long as the basic relationship between linear and angular motion as
mjr 100:1ff35c07217c 28 // shown in the diagram be achieved.)
mjr 100:1ff35c07217c 29 //
mjr 100:1ff35c07217c 30 //
mjr 100:1ff35c07217c 31 // Translating the angle to a linear position
mjr 100:1ff35c07217c 32 //
mjr 100:1ff35c07217c 33 // There are two complications to translating the angular reading back to
mjr 100:1ff35c07217c 34 // a linear plunger position.
mjr 100:1ff35c07217c 35 //
mjr 100:1ff35c07217c 36 // 1. We have to consider the sensor's zero point to be arbitrary. That means
mjr 100:1ff35c07217c 37 // that the zero point could be somewhere within the plunger's travel range,
mjr 100:1ff35c07217c 38 // so readings might "wrap" - e.g., we might see a series of readings when
mjr 100:1ff35c07217c 39 // the plunger is moving in one direction like 4050, 4070, 4090, 14, 34 (note
mjr 100:1ff35c07217c 40 // how we've "wrapped" past the 4096 boundary).
mjr 100:1ff35c07217c 41 //
mjr 100:1ff35c07217c 42 // To deal with this, we have to make a couple of assumptions:
mjr 100:1ff35c07217c 43 //
mjr 100:1ff35c07217c 44 // - The park position is at about 1/6 of the overall travel range
mjr 100:1ff35c07217c 45 // - The total angular travel range is less than one full revolution
mjr 100:1ff35c07217c 46 //
mjr 100:1ff35c07217c 47 // With those assumptions in hand, we can bias the raw readings to the
mjr 100:1ff35c07217c 48 // park position, and then take them modulo the raw scale. That will
mjr 100:1ff35c07217c 49 // ensure that readings wrap properly, regardless of where the raw zero
mjr 100:1ff35c07217c 50 // point lies.
mjr 100:1ff35c07217c 51 //
mjr 100:1ff35c07217c 52 // 2. Going back to the original diagram, you can see that the angle doesn't
mjr 100:1ff35c07217c 53 // vary linearly with the plunger position. It actually varies sinusoidally.
mjr 100:1ff35c07217c 54 // Let's use the vertical line between the plunger and the rotation point as
mjr 100:1ff35c07217c 55 // the zero-degree reference point. To figure the plunger position, then,
mjr 100:1ff35c07217c 56 // we need to figure the difference between the raw angle reading and the
mjr 100:1ff35c07217c 57 // zero-degree point; call this theta. Let L be the position of the plunger
mjr 100:1ff35c07217c 58 // relative to the vertical reference point, let D be the length of the
mjr 100:1ff35c07217c 59 // vertical reference point line, and let H by the distance from the rotation
mjr 100:1ff35c07217c 60 // point to the plunger connection point. This is a right triangle with
mjr 100:1ff35c07217c 61 // hypotenuse H and sides L and D. D is a constant, because the rotation
mjr 100:1ff35c07217c 62 // point never moves, and the plunger never moves vertically. Thus we can
mjr 100:1ff35c07217c 63 // calculate D = H*cos(theta) and L = H*sin(theta). D is a constant, so
mjr 100:1ff35c07217c 64 // we can figure H = D/cos(theta) hence L = D*sin(theta)/cos(theta) or
mjr 100:1ff35c07217c 65 // D*tan(theta). If we wanted to know the true position in real-world
mjr 100:1ff35c07217c 66 // units, we'd have to know D, but only need arbitrary linear units, so
mjr 100:1ff35c07217c 67 // we can choose whatever value for D we find convenient: in particular,
mjr 100:1ff35c07217c 68 // a value that gives us the desired range and resolution for the final
mjr 100:1ff35c07217c 69 // result.
mjr 100:1ff35c07217c 70 //
mjr 100:1ff35c07217c 71 // Note that the tangent diverges at +/-90 degrees, but that's not a problem
mjr 100:1ff35c07217c 72 // for the mechanical setup we've described, as the motion is inherently
mjr 100:1ff35c07217c 73 // limited to stay within this range.
mjr 100:1ff35c07217c 74 //
mjr 100:1ff35c07217c 75 // There's still one big piece missing here: we somehow have to know where
mjr 100:1ff35c07217c 76 // that vertical zero point lies. That's something we can only learn by
mjr 100:1ff35c07217c 77 // calibration. Unfortunately, we don't have a good way to detect this
mjr 100:1ff35c07217c 78 // directly. We *could* ask the user to look inside the cabinet and press
mjr 100:1ff35c07217c 79 // a button when the needle is straight up, but that seems too cumbersome.
mjr 100:1ff35c07217c 80 // What we'll do instead is provide some mechanical installation guidelines
mjr 100:1ff35c07217c 81 // about where the rotation point should be positioned, and then use the
mjr 100:1ff35c07217c 82 // full range to deduce the vertical position.
mjr 100:1ff35c07217c 83 //
mjr 100:1ff35c07217c 84 // The full range we actually have after calibration consists of the park
mjr 100:1ff35c07217c 85 // position and the maximum retracted position. We could in principle also
mjr 100:1ff35c07217c 86 // calibrate the maximum forward position, but that can't be read as reliably
mjr 100:1ff35c07217c 87 // as the other two, because the barrel spring makes it difficult for the
mjr 100:1ff35c07217c 88 // user to be sure they've pushed it all the way forward. Since we can
mjr 100:1ff35c07217c 89 // extract the information we need from the park and max retract positions,
mjr 100:1ff35c07217c 90 // it's better to rely on those alone and not ask for information that the
mjr 100:1ff35c07217c 91 // user can't as easily provide. Given these positions, AND the assumption
mjr 100:1ff35c07217c 92 // that the rotation point is at the midpoint of the plunger travel range,
mjr 100:1ff35c07217c 93 // we can do some rather grungy trig work to come up with a formula for the
mjr 100:1ff35c07217c 94 // angle between the park position and the vertical:
mjr 100:1ff35c07217c 95 //
mjr 100:1ff35c07217c 96 // let C1 = 1 1/32" (distance from midpoint to park),
mjr 100:1ff35c07217c 97 // C2 = 1 17/32" (distance from midpoint to max retract),
mjr 100:1ff35c07217c 98 // C = C2/C1 = 1.48484849,
mjr 100:1ff35c07217c 99 // alpha = angle from park to vertical,
mjr 100:1ff35c07217c 100 // beta = angle from max retract to vertical
mjr 100:1ff35c07217c 101 // theta = alpha + beta = angle from park to max retract, known from calibration,
mjr 100:1ff35c07217c 102 // T = tan(theta);
mjr 100:1ff35c07217c 103 //
mjr 100:1ff35c07217c 104 // then
mjr 100:1ff35c07217c 105 // alpha = atan(sqrt(4*T*T*C + C^2 + 2*C + 1) - C - 1)/(2*T*C))
mjr 100:1ff35c07217c 106 //
mjr 100:1ff35c07217c 107 // Did I mention this was grungy? At any rate, everything going into this
mjr 100:1ff35c07217c 108 // formula is either constant or known from the calibration, so we can
mjr 100:1ff35c07217c 109 // pre-compute alpha and store it after each calibration operation. And
mjr 100:1ff35c07217c 110 // knowing alpha, we can translate an angle reading from the sensor to an
mjr 100:1ff35c07217c 111 // angle relative to the vertical, which we can plug into D*tan(angle) to
mjr 100:1ff35c07217c 112 // get a linear reading.
mjr 100:1ff35c07217c 113 //
mjr 100:1ff35c07217c 114 // If you're wondering how we derived that ugly formula, read on. Start
mjr 100:1ff35c07217c 115 // with the basic relationships D*tan(alpha) = C1 and D*tan(beta) = C2.
mjr 100:1ff35c07217c 116 // This lets us write tan(beta) in terms of tan(alpha) as
mjr 100:1ff35c07217c 117 // C2/C1*tan(alpha) = C*tan(alpha). We can combine this with an identity
mjr 100:1ff35c07217c 118 // for the tan of a sum of angles:
mjr 100:1ff35c07217c 119 //
mjr 100:1ff35c07217c 120 // tan(alpha + beta) = (tan(alpha) + tan(beta))/(1 - tan(alpha)*tan(beta))
mjr 100:1ff35c07217c 121 //
mjr 100:1ff35c07217c 122 // to obtain:
mjr 100:1ff35c07217c 123 //
mjr 100:1ff35c07217c 124 // tan(theta) = tan(alpha + beta) = (1 + C*tan(alpha))/(1 - C*tan^2(alpha))
mjr 100:1ff35c07217c 125 //
mjr 100:1ff35c07217c 126 // Everything here except alpha is known, so we now have a quadratic equation
mjr 100:1ff35c07217c 127 // for tan(alpha). We can solve that by cranking through the normal algorithm
mjr 100:1ff35c07217c 128 // for solving a quadratic equation, arriving at the solution above.
mjr 100:1ff35c07217c 129 //
mjr 100:1ff35c07217c 130 //
mjr 100:1ff35c07217c 131 // Choosing an install position
mjr 100:1ff35c07217c 132 //
mjr 100:1ff35c07217c 133 // There are two competing factors in choosing the optimal "D". On the one
mjr 100:1ff35c07217c 134 // hand, you'd like D to be as large as possible, to maximum linearity of the
mjr 100:1ff35c07217c 135 // tan function used to translate angle to linear position. Higher linearity
mjr 100:1ff35c07217c 136 // gives us greater immunity to variations in the precise centering of the
mjr 100:1ff35c07217c 137 // rotation axis in the plunger travel range. tan() is pretty linear within
mjr 100:1ff35c07217c 138 // about +/- 30 degrees. On the other hand, you'd like D to be as small as
mjr 100:1ff35c07217c 139 // possible so that we get the largest overall angle range. Our sensor has
mjr 100:1ff35c07217c 140 // a fixed angular resolution, so the more of the overall circle we use, the
mjr 100:1ff35c07217c 141 // more sensor increments we have over the range, and thus the better
mjr 100:1ff35c07217c 142 // effective linear resolution.
mjr 100:1ff35c07217c 143 //
mjr 100:1ff35c07217c 144 // Let's do some calculations for various "D" values (vertical distance
mjr 100:1ff35c07217c 145 // between rotation point and plunger rod). For the effective DPI, we'll
mjr 100:1ff35c07217c 146 // 12-bit angular resolution, per the AEAT-6012 sensor.
mjr 100:1ff35c07217c 147 //
mjr 100:1ff35c07217c 148 // D theta(max) eff dpi theta(park)
mjr 100:1ff35c07217c 149 // -----------------------------------------------
mjr 100:1ff35c07217c 150 // 1 17/32" 45 deg 341 34 deg
mjr 100:1ff35c07217c 151 // 2" 37 deg 280 27 deg
mjr 100:1ff35c07217c 152 // 2 21/32" 30 deg 228 21 deg
mjr 100:1ff35c07217c 153 // 3 1/4" 25 deg 190 17 deg
mjr 100:1ff35c07217c 154 // 4 3/16" 20 deg 152 14 deg
mjr 100:1ff35c07217c 155 //
mjr 100:1ff35c07217c 156 // I'd consider 50 dpi to be the minimum for acceptable performance, 100 dpi
mjr 100:1ff35c07217c 157 // to be excellent, and anything above 300 dpi to be diminishing returns. So
mjr 100:1ff35c07217c 158 // for a 12-bit sensor, 2" looks like the sweet spot. It doesn't take us far
mjr 100:1ff35c07217c 159 // outside of the +/-30 deg zone of tan() linearity, and it achieves almost
mjr 100:1ff35c07217c 160 // 300 dpi of effective linear resolution. I'd stop there are not try to
mjr 100:1ff35c07217c 161 // push the angular resolution higher with a shorter D; with the 45 deg
mjr 100:1ff35c07217c 162 // theta(max) at D = 1-17/32", we'd get a lovely DPI level of 341, but at
mjr 100:1ff35c07217c 163 // the cost of getting pretty non-linear around the ends of the plunger
mjr 100:1ff35c07217c 164 // travel. Our math corrects for the non-linearity, but the more of that
mjr 100:1ff35c07217c 165 // correction we need, the more sensitive the whole contraption becomes to
mjr 100:1ff35c07217c 166 // getting the sensor positioning exactly right. The closer we can stay to
mjr 100:1ff35c07217c 167 // the linear approximation, the more tolerant we are of inexact sensor
mjr 100:1ff35c07217c 168 // positioning.
mjr 100:1ff35c07217c 169 //
mjr 100:1ff35c07217c 170 //
mjr 100:1ff35c07217c 171 // Supported sensors
mjr 100:1ff35c07217c 172 //
mjr 100:1ff35c07217c 173 // * AEAT-6012-A06. This is a magnetic absolute encoder with 12-bit
mjr 100:1ff35c07217c 174 // resolution. It linearly encodes one full (360 degree) rotation in
mjr 100:1ff35c07217c 175 // 4096 increments, so each increment represents 360/4096 = .088 degrees.
mjr 100:1ff35c07217c 176 //
mjr 100:1ff35c07217c 177 // The base class doesn't actually care much about the sensor type; all it
mjr 100:1ff35c07217c 178 // needs from the sensor is an angle reading represented on an arbitrary
mjr 100:1ff35c07217c 179 // linear scale. ("Linear" in the angle, so that one increment represents
mjr 100:1ff35c07217c 180 // a fixed number of degrees of arc. The full scale can represent one full
mjr 100:1ff35c07217c 181 // turn but doesn't have to, as long as the scale is linear over the range
mjr 100:1ff35c07217c 182 // covered.) To add new sensor types, you just need to add the code to
mjr 100:1ff35c07217c 183 // interface to the physical sensor and return its reading on an arbitrary
mjr 100:1ff35c07217c 184 // linear scale.
mjr 100:1ff35c07217c 185
mjr 100:1ff35c07217c 186 #ifndef _ROTARYSENSOR_H_
mjr 100:1ff35c07217c 187 #define _ROTARYSENSOR_H_
mjr 100:1ff35c07217c 188
mjr 100:1ff35c07217c 189 #include "FastInterruptIn.h"
mjr 100:1ff35c07217c 190 #include "AEAT6012.h"
mjr 100:1ff35c07217c 191
mjr 100:1ff35c07217c 192 // The conversion from raw sensor reading to linear position involves a
mjr 100:1ff35c07217c 193 // bunch of translations to different scales and unit systems. To help
mjr 100:1ff35c07217c 194 // keep things straight, let's give each scale a name:
mjr 100:1ff35c07217c 195 //
mjr 100:1ff35c07217c 196 // * "Raw" refers to the readings directly from the sensor. These are
mjr 102:41d49e78c253 197 // unsigned ints in the range 0..maRawxAngle, and represent angles in a
mjr 102:41d49e78c253 198 // unit system where one increment equals 360/maxRawAngle degrees. The
mjr 100:1ff35c07217c 199 // zero point is arbitrary, determined by the physical orientation
mjr 100:1ff35c07217c 200 // of the sensor.
mjr 100:1ff35c07217c 201 //
mjr 100:1ff35c07217c 202 // * "Biased" refers to angular units with a zero point equal to the
mjr 100:1ff35c07217c 203 // park position. This uses the same units as the "raw" system, but
mjr 100:1ff35c07217c 204 // the zero point is adjusted so that 0 always means the park position.
mjr 100:1ff35c07217c 205 // Negative values are forward of the park position. This scale is
mjr 100:1ff35c07217c 206 // also adjusted for wrapping, by ensuring that the value lies in the
mjr 100:1ff35c07217c 207 // range -(maximum forward excursion) to +(scale max - max fwd excursion).
mjr 100:1ff35c07217c 208 // Any values below or above the range are bumped up or down (respectively)
mjr 100:1ff35c07217c 209 // to wrap them back into the range.
mjr 100:1ff35c07217c 210 //
mjr 100:1ff35c07217c 211 // * "Linear" refers to the final linear results, in joystick units, on
mjr 100:1ff35c07217c 212 // the abstract integer scale from 0..65535 used by the generic plunger
mjr 100:1ff35c07217c 213 // base class.
mjr 100:1ff35c07217c 214 //
mjr 100:1ff35c07217c 215 class PlungerSensorRotary: public PlungerSensor
mjr 100:1ff35c07217c 216 {
mjr 100:1ff35c07217c 217 public:
mjr 102:41d49e78c253 218 PlungerSensorRotary(int maxRawAngle, float radiansPerSensorUnit) :
mjr 100:1ff35c07217c 219 PlungerSensor(65535),
mjr 102:41d49e78c253 220 maxRawAngle(maxRawAngle),
mjr 100:1ff35c07217c 221 radiansPerSensorUnit(radiansPerSensorUnit)
mjr 100:1ff35c07217c 222 {
mjr 100:1ff35c07217c 223 // start our sample timer with an arbitrary zero point of now
mjr 100:1ff35c07217c 224 timer.start();
mjr 100:1ff35c07217c 225
mjr 100:1ff35c07217c 226 // clear the timing statistics
mjr 100:1ff35c07217c 227 nReads = 0;
mjr 100:1ff35c07217c 228 totalReadTime = 0;
mjr 100:1ff35c07217c 229
mjr 100:1ff35c07217c 230 // Pre-calculate the maximum forward excursion distance, in raw
mjr 100:1ff35c07217c 231 // units. For our reference mechanical setup with "D" in a likely
mjr 100:1ff35c07217c 232 // range, theta(max) is always about 10 degrees higher than
mjr 100:1ff35c07217c 233 // theta(park). 10 degrees is about 1/36 of the overall circle,
mjr 100:1ff35c07217c 234 // which is the same as 1/36 of the sensor scale. To be
mjr 100:1ff35c07217c 235 // conservative, allow for about 3X that, so allow 1/12 of scale
mjr 100:1ff35c07217c 236 // as the maximum forward excursion. For wrapping purposes, we'll
mjr 100:1ff35c07217c 237 // consider any reading outside of the range from -(excursion)
mjr 102:41d49e78c253 238 // to +(maxRawAngle - excursion) to be wrapped.
mjr 102:41d49e78c253 239 maxForwardExcursionRaw = maxRawAngle/12;
mjr 100:1ff35c07217c 240
mjr 100:1ff35c07217c 241 // reset the calibration counters
mjr 100:1ff35c07217c 242 biasedMinObserved = biasedMaxObserved = 0;
mjr 100:1ff35c07217c 243 }
mjr 100:1ff35c07217c 244
mjr 100:1ff35c07217c 245 // Restore the saved calibration at startup
mjr 100:1ff35c07217c 246 virtual void restoreCalibration(Config &cfg)
mjr 100:1ff35c07217c 247 {
mjr 100:1ff35c07217c 248 // only proceed if there's calibration data to retrieve
mjr 100:1ff35c07217c 249 if (cfg.plunger.cal.calibrated)
mjr 100:1ff35c07217c 250 {
mjr 100:1ff35c07217c 251 // we store the raw park angle in raw0
mjr 100:1ff35c07217c 252 rawParkAngle = cfg.plunger.cal.raw0;
mjr 100:1ff35c07217c 253
mjr 100:1ff35c07217c 254 // we store biased max angle in raw1
mjr 100:1ff35c07217c 255 biasedMax = cfg.plunger.cal.raw1;
mjr 100:1ff35c07217c 256 }
mjr 100:1ff35c07217c 257 else
mjr 100:1ff35c07217c 258 {
mjr 100:1ff35c07217c 259 // Use the current sensor reading as the initial guess at the
mjr 100:1ff35c07217c 260 // park position. The system is usually powered up with the
mjr 100:1ff35c07217c 261 // plunger at the neutral position, so this is a good guess in
mjr 100:1ff35c07217c 262 // most cases. If the plunger has been calibrated, we'll restore
mjr 100:1ff35c07217c 263 // the better guess when we restore the configuration later on in
mjr 100:1ff35c07217c 264 // the initialization process.
mjr 100:1ff35c07217c 265 rawParkAngle = 0;
mjr 100:1ff35c07217c 266 readSensor(rawParkAngle);
mjr 100:1ff35c07217c 267
mjr 100:1ff35c07217c 268 // Set an initial wild guess at a range equal to +/-35 degrees.
mjr 100:1ff35c07217c 269 // Note that this is in the "biased" coordinate system - raw
mjr 100:1ff35c07217c 270 // units, but relative to the park angle. The park angle is
mjr 102:41d49e78c253 271 // about -25 degrees in this setup.
mjr 102:41d49e78c253 272 biasedMax = (35 + 25) * maxRawAngle/360;
mjr 100:1ff35c07217c 273 }
mjr 100:1ff35c07217c 274
mjr 100:1ff35c07217c 275 // recalculate the vertical angle
mjr 100:1ff35c07217c 276 updateAlpha();
mjr 100:1ff35c07217c 277 }
mjr 100:1ff35c07217c 278
mjr 100:1ff35c07217c 279 // Begin calibration
mjr 100:1ff35c07217c 280 virtual void beginCalibration(Config &)
mjr 100:1ff35c07217c 281 {
mjr 100:1ff35c07217c 282 // Calibration starts out with the plunger at the park position, so
mjr 100:1ff35c07217c 283 // we can take the current sensor reading to be the park position.
mjr 100:1ff35c07217c 284 rawParkAngle = 0;
mjr 100:1ff35c07217c 285 readSensor(rawParkAngle);
mjr 100:1ff35c07217c 286
mjr 100:1ff35c07217c 287 // Reset the observed calibration counters
mjr 100:1ff35c07217c 288 biasedMinObserved = biasedMaxObserved = 0;
mjr 100:1ff35c07217c 289 }
mjr 100:1ff35c07217c 290
mjr 100:1ff35c07217c 291 // End calibration
mjr 100:1ff35c07217c 292 virtual void endCalibration(Config &cfg)
mjr 100:1ff35c07217c 293 {
mjr 100:1ff35c07217c 294 // apply the observed maximum angle
mjr 100:1ff35c07217c 295 biasedMax = biasedMaxObserved;
mjr 100:1ff35c07217c 296
mjr 100:1ff35c07217c 297 // recalculate the vertical angle
mjr 100:1ff35c07217c 298 updateAlpha();
mjr 100:1ff35c07217c 299
mjr 100:1ff35c07217c 300 // save our raw configuration data
mjr 100:1ff35c07217c 301 cfg.plunger.cal.raw0 = static_cast<uint16_t>(rawParkAngle);
mjr 100:1ff35c07217c 302 cfg.plunger.cal.raw1 = static_cast<uint16_t>(biasedMax);
mjr 100:1ff35c07217c 303
mjr 100:1ff35c07217c 304 // Refigure the range for the generic code
mjr 100:1ff35c07217c 305 cfg.plunger.cal.min = biasedAngleToLinear(biasedMinObserved);
mjr 100:1ff35c07217c 306 cfg.plunger.cal.max = biasedAngleToLinear(biasedMaxObserved);
mjr 100:1ff35c07217c 307 cfg.plunger.cal.zero = biasedAngleToLinear(0);
mjr 100:1ff35c07217c 308 }
mjr 100:1ff35c07217c 309
mjr 100:1ff35c07217c 310 // figure the average scan time in microseconds
mjr 100:1ff35c07217c 311 virtual uint32_t getAvgScanTime()
mjr 100:1ff35c07217c 312 {
mjr 100:1ff35c07217c 313 return nReads == 0 ? 0 : static_cast<uint32_t>(totalReadTime / nReads);
mjr 100:1ff35c07217c 314 }
mjr 100:1ff35c07217c 315
mjr 100:1ff35c07217c 316 // read the sensor
mjr 100:1ff35c07217c 317 virtual bool readRaw(PlungerReading &r)
mjr 100:1ff35c07217c 318 {
mjr 100:1ff35c07217c 319 // note the starting time for the reading
mjr 100:1ff35c07217c 320 uint32_t t0 = timer.read_us();
mjr 100:1ff35c07217c 321
mjr 100:1ff35c07217c 322 // read the angular position
mjr 100:1ff35c07217c 323 int angle;
mjr 100:1ff35c07217c 324 if (!readSensor(angle))
mjr 100:1ff35c07217c 325 return false;
mjr 102:41d49e78c253 326
mjr 100:1ff35c07217c 327 // Refigure the angle relative to the raw park position. This
mjr 100:1ff35c07217c 328 // is the "biased" angle.
mjr 100:1ff35c07217c 329 angle -= rawParkAngle;
mjr 100:1ff35c07217c 330
mjr 100:1ff35c07217c 331 // Adjust for wrapping.
mjr 100:1ff35c07217c 332 //
mjr 100:1ff35c07217c 333 // An angular sensor reports the position on a circular scale, for
mjr 100:1ff35c07217c 334 // obvious reasons, so there's some point along the circle where the
mjr 100:1ff35c07217c 335 // angle is zero. One tick before that point reads as the maximum
mjr 100:1ff35c07217c 336 // angle on the scale, so we say that the scale "wraps" at that point.
mjr 100:1ff35c07217c 337 //
mjr 100:1ff35c07217c 338 // To correct for this, we can look to the layout of the mechanical
mjr 100:1ff35c07217c 339 // setup to constrain the values. Consider anything below the maximum
mjr 100:1ff35c07217c 340 // forward exclusion to be wrapped on the low side, and consider
mjr 100:1ff35c07217c 341 // anything outside of the complementary range on the high side to
mjr 100:1ff35c07217c 342 // be wrapped on the high side.
mjr 102:41d49e78c253 343 if (angle < -maxForwardExcursionRaw)
mjr 102:41d49e78c253 344 angle += maxRawAngle;
mjr 102:41d49e78c253 345 else if (angle >= maxRawAngle - maxForwardExcursionRaw)
mjr 102:41d49e78c253 346 angle -= maxRawAngle;
mjr 100:1ff35c07217c 347
mjr 100:1ff35c07217c 348 // Note if this is the highest/lowest observed reading on the biased
mjr 100:1ff35c07217c 349 // scale since the last calibration started.
mjr 100:1ff35c07217c 350 if (angle > biasedMaxObserved)
mjr 100:1ff35c07217c 351 biasedMaxObserved = angle;
mjr 100:1ff35c07217c 352 if (angle < biasedMinObserved)
mjr 100:1ff35c07217c 353 biasedMinObserved = angle;
mjr 100:1ff35c07217c 354
mjr 100:1ff35c07217c 355 // figure the linear result
mjr 100:1ff35c07217c 356 r.pos = biasedAngleToLinear(angle);
mjr 102:41d49e78c253 357
mjr 100:1ff35c07217c 358 // Set the timestamp on the reading to right now
mjr 100:1ff35c07217c 359 uint32_t now = timer.read_us();
mjr 100:1ff35c07217c 360 r.t = now;
mjr 100:1ff35c07217c 361
mjr 100:1ff35c07217c 362 // count the read statistics
mjr 100:1ff35c07217c 363 totalReadTime += now - t0;
mjr 100:1ff35c07217c 364 nReads += 1;
mjr 100:1ff35c07217c 365
mjr 100:1ff35c07217c 366 // success
mjr 100:1ff35c07217c 367 return true;
mjr 100:1ff35c07217c 368 }
mjr 100:1ff35c07217c 369
mjr 100:1ff35c07217c 370 private:
mjr 100:1ff35c07217c 371 // Read the underlying sensor - implemented by the hardware-specific
mjr 100:1ff35c07217c 372 // subclasses. Returns true on success, false if the sensor can't
mjr 100:1ff35c07217c 373 // be read. The angle is returned in raw sensor units.
mjr 100:1ff35c07217c 374 virtual bool readSensor(int &angle) = 0;
mjr 100:1ff35c07217c 375
mjr 100:1ff35c07217c 376 // Convert a biased angle value to a linear reading
mjr 100:1ff35c07217c 377 int biasedAngleToLinear(int angle)
mjr 100:1ff35c07217c 378 {
mjr 100:1ff35c07217c 379 // Translate to an angle relative to the vertical, in sensor units
mjr 102:41d49e78c253 380 float theta = static_cast<float>(angle)*radiansPerSensorUnit - alpha;
mjr 100:1ff35c07217c 381
mjr 102:41d49e78c253 382 // Calculate the linear position relative to the vertical. Zero
mjr 102:41d49e78c253 383 // is right at the intersection of the vertical line from the
mjr 102:41d49e78c253 384 // sensor rotation center to the plunger axis; positive numbers
mjr 102:41d49e78c253 385 // are behind the vertical (more retracted).
mjr 102:41d49e78c253 386 int linearPos = static_cast<int>(tanf(theta) * linearScaleFactor);
mjr 100:1ff35c07217c 387
mjr 102:41d49e78c253 388 // Finally, figure the offset. The vertical is the halfway point
mjr 102:41d49e78c253 389 // of the plunger motion, so we want to put it at half of the raw
mjr 102:41d49e78c253 390 // scale of 0..65535.
mjr 102:41d49e78c253 391 return linearPos + 32767;
mjr 100:1ff35c07217c 392 }
mjr 100:1ff35c07217c 393
mjr 100:1ff35c07217c 394 // Update the estimation of the vertical angle, based on the angle
mjr 100:1ff35c07217c 395 // between the park position and maximum retraction point.
mjr 100:1ff35c07217c 396 void updateAlpha()
mjr 100:1ff35c07217c 397 {
mjr 100:1ff35c07217c 398 // See the comments at the top of the file for details on this
mjr 100:1ff35c07217c 399 // formula. This figures the angle between the park position
mjr 100:1ff35c07217c 400 // and the vertical by applying the known constraints of the
mjr 100:1ff35c07217c 401 // mechanical setup: the known length of a standard plunger,
mjr 100:1ff35c07217c 402 // and the requirement that the rotation axis be placed at
mjr 100:1ff35c07217c 403 // roughly the midpoint of the plunger travel.
mjr 100:1ff35c07217c 404 const float C = 1.4848489f; // 1-17/32" / 1-1/32"
mjr 102:41d49e78c253 405 float maxInRadians = static_cast<float>(biasedMax) * radiansPerSensorUnit;
mjr 102:41d49e78c253 406 float T = tanf(maxInRadians);
mjr 102:41d49e78c253 407 alpha = atanf((sqrtf(4*T*T*C + C*C + 2*C + 1) - C - 1)/(2*T*C));
mjr 102:41d49e78c253 408
mjr 102:41d49e78c253 409 // While we're at it, figure the linear conversion factor. Alpha
mjr 102:41d49e78c253 410 // represents the angle from the park position to the midpoint,
mjr 102:41d49e78c253 411 // which in the real world represents about 31/32", or just less
mjr 102:41d49e78c253 412 // then 1/3 of the overall travel. We want to normalize this to
mjr 102:41d49e78c253 413 // the corresponding fraction of our 0..65535 abstract linear unit
mjr 102:41d49e78c253 414 // system. To avoid overflow, normalize to a slightly smaller
mjr 102:41d49e78c253 415 // scale.
mjr 100:1ff35c07217c 416 const float safeMax = 60000.0f;
mjr 102:41d49e78c253 417 const float alphaInLinearUnits = safeMax * .316327f; // 31/22" / 3-1/16"
mjr 102:41d49e78c253 418 linearScaleFactor = static_cast<int>(alphaInLinearUnits / tanf(alpha));
mjr 100:1ff35c07217c 419 }
mjr 100:1ff35c07217c 420
mjr 100:1ff35c07217c 421 // Maximum raw angular reading from the sensor. The sensor's readings
mjr 102:41d49e78c253 422 // will always be on a scale from 0..maxRawAngle.
mjr 102:41d49e78c253 423 int maxRawAngle;
mjr 100:1ff35c07217c 424
mjr 100:1ff35c07217c 425 // Radians per sensor unit. This is a constant for the sensor.
mjr 100:1ff35c07217c 426 float radiansPerSensorUnit;
mjr 100:1ff35c07217c 427
mjr 100:1ff35c07217c 428 // Pre-calculated value of the maximum forward excursion, in raw units.
mjr 102:41d49e78c253 429 int maxForwardExcursionRaw;
mjr 100:1ff35c07217c 430
mjr 100:1ff35c07217c 431 // Raw reading at the park position. We use this to handle "wrapping",
mjr 100:1ff35c07217c 432 // if the sensor's raw zero reading position is within the plunger travel
mjr 100:1ff35c07217c 433 // range. All readings are taken to be within
mjr 100:1ff35c07217c 434 int rawParkAngle;
mjr 100:1ff35c07217c 435
mjr 100:1ff35c07217c 436 // Biased maximum angle. This is the angle at the maximum retracted
mjr 100:1ff35c07217c 437 // position, in biased units (sensor units, relative to the park angle).
mjr 100:1ff35c07217c 438 int biasedMax;
mjr 100:1ff35c07217c 439
mjr 100:1ff35c07217c 440 // Mininum and maximum angle observed since last calibration start, on
mjr 100:1ff35c07217c 441 // the biased scale
mjr 100:1ff35c07217c 442 int biasedMinObserved;
mjr 100:1ff35c07217c 443 int biasedMaxObserved;
mjr 100:1ff35c07217c 444
mjr 100:1ff35c07217c 445 // The "alpha" angle - the angle between the park position and the
mjr 100:1ff35c07217c 446 // vertical line between the rotation axis and the plunger. This is
mjr 102:41d49e78c253 447 // represented in radians.
mjr 102:41d49e78c253 448 float alpha;
mjr 100:1ff35c07217c 449
mjr 100:1ff35c07217c 450 // The linear scaling factor, applied in our trig calculation from
mjr 100:1ff35c07217c 451 // angle to linear position. This corresponds to the distance from
mjr 100:1ff35c07217c 452 // the rotation center to the plunger rod, but since the linear result
mjr 100:1ff35c07217c 453 // is in abstract joystick units, this distance is likewise in abstract
mjr 100:1ff35c07217c 454 // units. The value isn't chosen to correspond to any real-world
mjr 100:1ff35c07217c 455 // distance units, but rather to yield a joystick result that takes
mjr 100:1ff35c07217c 456 // advantage of most of the available axis range, to minimize rounding
mjr 100:1ff35c07217c 457 // errors when converting between scales.
mjr 100:1ff35c07217c 458 float linearScaleFactor;
mjr 100:1ff35c07217c 459
mjr 100:1ff35c07217c 460 // timer for input timestamps and read timing measurements
mjr 100:1ff35c07217c 461 Timer timer;
mjr 100:1ff35c07217c 462
mjr 100:1ff35c07217c 463 // read timing statistics
mjr 100:1ff35c07217c 464 uint64_t totalReadTime;
mjr 100:1ff35c07217c 465 uint64_t nReads;
mjr 100:1ff35c07217c 466
mjr 100:1ff35c07217c 467 // Keep track of when calibration is in progress. The calibration
mjr 100:1ff35c07217c 468 // procedure is usually handled by the generic main loop code, but
mjr 100:1ff35c07217c 469 // in this case, we have to keep track of some of the raw sensor
mjr 100:1ff35c07217c 470 // data during calibration for our own internal purposes.
mjr 100:1ff35c07217c 471 bool calibrating;
mjr 100:1ff35c07217c 472 };
mjr 100:1ff35c07217c 473
mjr 100:1ff35c07217c 474 // Specialization for the AEAT-601X sensors
mjr 100:1ff35c07217c 475 template<int nDataBits> class PlungerSensorAEAT601X : public PlungerSensorRotary
mjr 100:1ff35c07217c 476 {
mjr 100:1ff35c07217c 477 public:
mjr 100:1ff35c07217c 478 PlungerSensorAEAT601X(PinName csPin, PinName clkPin, PinName doPin) :
mjr 100:1ff35c07217c 479 PlungerSensorRotary((1 << nDataBits) - 1, 6.283185f/((1 << nDataBits) - 1)),
mjr 100:1ff35c07217c 480 aeat(csPin, clkPin, doPin)
mjr 100:1ff35c07217c 481 {
mjr 100:1ff35c07217c 482 // Make sure the sensor has had time to finish initializing.
mjr 100:1ff35c07217c 483 // Power-up time (tCF) from the data sheet is 20ms for the 12-bit
mjr 100:1ff35c07217c 484 // version, 50ms for the 10-bit version.
mjr 100:1ff35c07217c 485 wait_ms(nDataBits == 12 ? 20 :
mjr 100:1ff35c07217c 486 nDataBits == 10 ? 50 :
mjr 100:1ff35c07217c 487 50);
mjr 100:1ff35c07217c 488 }
mjr 100:1ff35c07217c 489
mjr 100:1ff35c07217c 490 // read the angle
mjr 100:1ff35c07217c 491 virtual bool readSensor(int &angle)
mjr 100:1ff35c07217c 492 {
mjr 100:1ff35c07217c 493 angle = aeat.readAngle();
mjr 100:1ff35c07217c 494 return true;
mjr 100:1ff35c07217c 495 }
mjr 100:1ff35c07217c 496
mjr 100:1ff35c07217c 497 protected:
mjr 100:1ff35c07217c 498 // physical sensor interface
mjr 100:1ff35c07217c 499 AEAT601X<nDataBits> aeat;
mjr 100:1ff35c07217c 500 };
mjr 100:1ff35c07217c 501
mjr 100:1ff35c07217c 502 #endif