Lab10 Preview Report - Jian-PingWang/EE2405 GitHub Wiki

Topics

  • Motor controls with microcontrollers
  • Compass sensors

Motor controls with microcontrollers

  • Introduction

由於馬達控制專用數位訊號處理器主要支援大型離線馬達(off-line motor)，其成本對 於小型馬達控制系統通常太高，這使得小型通用微控制器在多數情形下已成為小型馬達控制應用的最低成本解決方案。

  • Related parts of our labs

本次 lab 將學習 servo control，也就是一種 programmable electric motors 的基本操作。

Servos are controlled by sending them a pulse of variable width. The control wire is used to send this pulse. The parameters for this pulse are that it has a minimum pulse, a maximum pulse, and a repetition rate. Given the rotation constraints of the servo, neutral is defined to be the position where the servo has exactly the same amount of potential rotation in the clockwise direction as it does in the counter clockwise direction. It is important to note that different servos will have different constraints on their rotation but they all have a neutral position, and that position is always around 1.5 milliseconds (ms).

The angle is determined by the duration of a pulse that is applied to the control wire. This is called Pulse width Modulation. The servo expects to see a pulse every 20 ms. The length of the pulse will determine how far the motor turns. For example, a 1.5 ms pulse will make the motor turn to the 90 degree position (neutral position).

When these servos are commanded to move they will move to the position and hold that position. If an external force pushes against the servo while the servo is holding a position, the servo will resist from moving out of that position. The maximum amount of force the servo can exert is the torque rating of the servo. Servos will not hold their position forever though; the position pulse must be repeated to instruct the servo to stay in position.

  • Questions about the topic or our lab

目前尚無。

Compass sensors

  • Introduction

三維電子羅盤由三維磁阻感測器、雙軸傾角感測器和MCU構成。三維磁阻感測器用來測量地球磁場，傾角感測器是在磁力儀非水平狀態時進行補償；MCU處理磁力儀和傾角感測器的信號以及數據輸出和軟鐵、硬鐵補償。該磁力儀是採用三個互相垂直的磁阻感測器，每個軸向上的感測器檢測在該方向上的地 磁場強度。向前的方向稱為x方向的感測器檢測地磁場在x方向的矢量值；向左或Y方向的感測器檢測地磁場在Y方向的矢量值；向下或Z方向的感測器檢測地磁場在Z方向的矢量值。每個方向的感測器的靈敏度都已根據在該方向上 地磁場的分矢量調整到最佳點，並具有非常低的橫軸靈敏度。感測器產生的模擬輸出信號進行放大後送入MCU進行處理。磁場測量範圍為±2Gauss。通過採用12位 A/D轉換器，磁力儀能夠分辨出小於1mGauss的磁場變化量，我們便可通過該高分辨力來準確測量出200-300mGauss的X和Y方向的磁場強度，不論是在赤道上的向上變化還是在南北極的更低值位置。

而在整個補償技術中Z軸向的矢量扮演一個非常重要的角色。要正確運用這些值，俯仰和側傾角的數字必須時刻更新。採用雙軸寬線性量程範圍、高解析度、溫漂係數低的陶瓷基體電解質感測器來測量俯仰角和側傾角，傾角數值經過電路板上的溫度感測器補償后得出的。

  • Related parts of our labs

本次 lab 將學習 HMC5883L 的基本操作與原理。

  • Questions about the topic or our lab

目前尚無。