Encoder Calibration System

This document details the implementation of an encoder calibration system for precise stepper motor position control.

1. System Overview

Basic Architecture

class EncoderBase {
    typedef struct {
        uint16_t rawAngle;          // raw data
        uint16_t rectifiedAngle;    // calibrated rawAngle data
        bool rectifyValid;
    } AngleData_t;
 
    const int32_t RESOLUTION = ((int32_t)((0x00000001U) << 14)); // 16384 points
};

Key features:

• 14-bit resolution (16384 positions)
• Raw and calibrated angle tracking
• Validation system for calibration data

2. Calibration Process

State Machine

typedef enum {
    CALI_DISABLE = 0x00,
    CALI_FORWARD_PREPARE,
    CALI_FORWARD_MEASURE,
    CALI_BACKWARD_RETURN,
    CALI_BACKWARD_GAP_DISMISS,
    CALI_BACKWARD_MEASURE,
    CALI_CALCULATING,
} State_t;

Calibration steps:

1. Forward preparation
2. Forward measurement
3. Backward return
4. Gap dismissal
5. Backward measurement
6. Data calculation

3. Measurement System

Data Collection

static const int32_t MOTOR_ONE_CIRCLE_HARD_STEPS = 200;   // 1.8° steps
static const uint8_t SAMPLE_COUNTS_PER_STEP = 16;
static const uint8_t AUTO_CALIB_SPEED = 2;
static const uint8_t FINE_TUNE_CALIB_SPEED = 1;

Features:

• Multiple samples per step
• Bi-directional measurement
• Automatic speed control
• Fine-tuning capabilities

Data Processing

int32_t CycleDataAverage(const uint16_t* _data, uint16_t _length, int32_t _cyc)
{
    // Cycle-aware averaging algorithm
    // Handles wraparound cases
    // Ensures consistent results
}

4. Validation System

Error Checking

typedef enum {
    CALI_NO_ERROR = 0x00,
    CALI_ERROR_AVERAGE_DIR,
    CALI_ERROR_AVERAGE_CONTINUTY,
    CALI_ERROR_PHASE_STEP,
    CALI_ERROR_ANALYSIS_QUANTITY,
} Error_t;

Validation checks:

• Direction consistency
• Data continuity
• Phase stepping
• Quantity analysis

Data Validation

void CalibrationDataCheck()
{
    // Check data direction
    // Verify data continuity
    // Validate step consistency
    // Confirm measurement accuracy
}

5. MT6816 Encoder Implementation

Initialization

bool MT6816Base::Init()
{
    SpiInit();
    UpdateAngle();
    
    // Validate calibration data
    angleData.rectifyValid = true;
    for (uint32_t i = 0; i < RESOLUTION; i++) {
        if (quickCaliDataPtr[i] == 0xFFFF)
            angleData.rectifyValid = false;
    }
}

Features:

• SPI communication setup
• Calibration data validation
• Quick lookup table initialization

Angle Reading

uint16_t MT6816Base::UpdateAngle()
{
    // Read raw angle data
    // Apply parity checking
    // Perform angle correction
    // Return calibrated value
}

6. Flash Management

Data Storage

void TickMainLoop()
{
    // Calculate calibration data
    ClearFlash();
    BeginWriteFlash();
    // Store calibration values
    EndWriteFlash();
}

Features:

• Safe flash writing
• Data integrity checks
• Error recovery
• System reset after calibration

7. Key Algorithms

Cycle Arithmetic

static uint32_t CycleMod(uint32_t _a, uint32_t _b)
static int32_t CycleSubtract(int32_t _a, int32_t _b, int32_t _cyc)
static int32_t CycleAverage(int32_t _a, int32_t _b, int32_t _cyc)

Implements:

• Modular arithmetic
• Wraparound handling
• Averaging with cycle awareness
• Delta calculations

8. System Benefits

1. Accuracy

   • High-resolution measurement
   • Multiple samples per position
   • Bi-directional validation
   • Error compensation

2. Reliability

   • Comprehensive error checking
   • Data validation
   • Flash data persistence
   • Recovery mechanisms

3. Performance

   • Fast angle updates
   • Efficient lookup table
   • Optimized calculations
   • Quick calibration process

4. Flexibility

   • Adaptable to different encoders
   • Configurable parameters
   • Multiple validation methods
   • Extensible architecture

This implementation provides a robust foundation for precise position feedback in stepper motor applications requiring high accuracy and reliability.