WPILib中的梯形运动轮廓

备注

本文介绍了梯形运动剖面的代码生成。文档将更详细地描述所涉及的概念。

备注

有关在基于命令的框架:ref:command-based framework <docs/software/commandbased/what-is-command-based:What Is “Command-Based” Programming?> , 请参阅 通过TrapezoidProfileSubsystems和TrapezoidProfileCommands进行运动分析.

备注

单独使用的“ TrapezoidProfile”类在与自定义控制器（例如具有内置PID功能的“智能”电机控制器）组合使用时最有用。要将其与WPILib的PIDController集成，请参阅 将运动分析和PID控制与ProfiledPIDController相结合.

尽管前馈和反馈控制提供了实现给定设定值的便捷方法，但我们仍然经常面临为我们的机构生成设定值的问题。尽管天真地立即将某种机制控制到所需状态的方法可能会起作用，但它通常不是最佳的。为了改善对机制的处理，我们通常希望命令机制达到一定的“设定值”序列，以便在其当前状态和所需目标状态之间平滑地内插。

To help users do this, WPILib provides a TrapezoidProfile class (Java, C++).

创建梯形轮廓

备注

在C ++中，“ TrapezoidProfile”类在用于距离测量的单位类型（可能是角度的或线性的）上模板化。传入的值*必须*具有与距离单位一致的单位，否则将引发编译时错误。有关C ++单元的更多信息，请参阅：docs / software / basic-programming / cpp-units：C ++单元库。

约束条件

备注

各种前馈帮助类 feedforward helper classes 提供了用于计算最大同时可达到的速度和机构加速度的方法。这些对于为您的``TrapezoidProfile’’计算适当的运动约束非常有用。

In order to create a trapezoidal motion profile, we must first impose some constraints on the desired motion. Namely, we must specify a maximum velocity and acceleration that the mechanism will be expected to achieve during the motion. To do this, we create an instance of the TrapezoidProfile.Constraints class (Java, C++):

JavaC++

// Creates a new set of trapezoidal motion profile constraints
// Max velocity of 10 meters per second
// Max acceleration of 20 meters per second squared
new TrapezoidProfile.Constraints(10, 20);

起始和结束状态

Next, we must specify the desired starting and ending states for our mechanisms using the TrapezoidProfile.State class (Java, C++). Each state has a position and a velocity:

JavaC++

// Creates a new state with a position of 5 meters
// and a velocity of 0 meters per second
new TrapezoidProfile.State(5, 0);

汇总

备注

C ++通常能够推断内部类的类型，因此可以将简单的初始化列表（没有类名）作为参数发送。为了清楚起见，完整的类名包含在下面的示例中。

既然我们知道如何创建一组约束和所需的开始/结束状态，我们就可以创建运动轮廓了。 TrapezoidProfile构造函数按顺序接受3个参数：约束，目标状态和初始状态。

JavaC++

// Creates a new TrapezoidProfile
// Profile will have a max vel of 5 meters per second
// Profile will have a max acceleration of 10 meters per second squared
// Profile will end stationary at 5 meters
// Profile will start stationary at zero position
TrapezoidProfile profile = new TrapezoidProfile(new TrapezoidProfile.Constraints(5, 10),
                                                new TrapezoidProfile.State(5, 0),
                                                new TrapezoidProfile.State(0, 0));

使用``TrapezoidProfile``

采样配置文件

创建了“ TrapezoidProfile”后，使用起来非常简单：要在配置文件启动后的给定时间获取配置文件状态，请调用calculate（）方法：

JavaC++

// Returns the motion profile state after 5 seconds of motion
profile.calculate(5);

使用状态

calculate方法返回一个TrapezoidProfile.State类（在构造配置文件时用于指定初始/结束状态的类）。要将其用于实际控制，只需将包含的位置和速度值传递到所需的任何控制器（例如PIDController）：

JavaC++

var setpoint = profile.calculate(elapsedTime);
controller.calculate(encoder.getDistance(), setpoint.position);

完整用法示例

备注

In this example, the profile is re-computed every timestep. This is a somewhat different usage technique than is detailed above, but works according to the same principles - the profile is sampled at a time corresponding to the loop period to get the setpoint for the next loop iteration.

在ElevatorTrapezoidProfile示例项目中提供了更完整的``TrapezoidProfile’’用法示例（Java，C ++）：

JavaC++

package edu.wpi.first.wpilibj.examples.elevatortrapezoidprofile;

import edu.wpi.first.math.controller.SimpleMotorFeedforward;
import edu.wpi.first.math.trajectory.TrapezoidProfile;
import edu.wpi.first.wpilibj.Joystick;
import edu.wpi.first.wpilibj.TimedRobot;

public class Robot extends TimedRobot {
  private static double kDt = 0.02;

  private final Joystick m_joystick = new Joystick(1);
  private final ExampleSmartMotorController m_motor = new ExampleSmartMotorController(1);
  // Note: These gains are fake, and will have to be tuned for your robot.
  private final SimpleMotorFeedforward m_feedforward = new SimpleMotorFeedforward(1, 1.5);

  private final TrapezoidProfile.Constraints m_constraints =
      new TrapezoidProfile.Constraints(1.75, 0.75);
  private TrapezoidProfile.State m_goal = new TrapezoidProfile.State();
  private TrapezoidProfile.State m_setpoint = new TrapezoidProfile.State();

  @Override
  public void robotInit() {
    // Note: These gains are fake, and will have to be tuned for your robot.
    m_motor.setPID(1.3, 0.0, 0.7);
  }

  @Override
  public void teleopPeriodic() {
    if (m_joystick.getRawButtonPressed(2)) {
      m_goal = new TrapezoidProfile.State(5, 0);
    } else if (m_joystick.getRawButtonPressed(3)) {
      m_goal = new TrapezoidProfile.State(0, 0);
    }

    // Create a motion profile with the given maximum velocity and maximum
    // acceleration constraints for the next setpoint, the desired goal, and the
    // current setpoint.
    var profile = new TrapezoidProfile(m_constraints, m_goal, m_setpoint);

    // Retrieve the profiled setpoint for the next timestep. This setpoint moves
    // toward the goal while obeying the constraints.
    m_setpoint = profile.calculate(kDt);

    // Send setpoint to offboard controller PID
    m_motor.setSetpoint(
        ExampleSmartMotorController.PIDMode.kPosition,
        m_setpoint.position,
        m_feedforward.calculate(m_setpoint.velocity) / 12.0);
  }
}