如何使用 Tkinter 为步进电机系统实现停止按钮？

Question

我有一个关于在Tkinter 中使用停止按钮的问题。

对于一个实验，我必须设置一个使用两个步进电机工作的 X/Y 平台。 arduino 程序完美运行。唯一的问题是，当我激活将舞台驱动到各种坐标的启动功能时，它会冻结。现在的问题是它必须连续运行数周，并且需要一个停止按钮来应对紧急情况并停止步进电机。停止按钮必须做两件事：它必须停止步进驱动电机，它必须打破tkinter.after 循环。但是，由于冻结，无法点击按钮。

这是我的代码：

import tkinter as tk
import serial

ser = serial.Serial('COM5', 115200)

running = False

def quit():
    """Function that closes the serial port and destroys the root of the GUI"""
    global root
    ser.close()
    root.destroy()
    
def route():
    """Writes coordinates to the arduino, which in return drives the stepper motors"""
    if running == True:
        # The g line stands for go to!
        ser.write(b'g115000\r\n')
        root.after(50)
        ser.write(b'g225000\r\n')
        root.after(30000)
        ser.write(b'g1400\r\n')
        root.after(50)
        ser.write(b'g2500\r\n')
        
    root.after(12000,route())

    
def zeroing():
    """Zeros the program, this is necessary for the stage to 
    calibrate it's boundary conditions"""
    #zeros the stage so that it is ready to use!
    varLabel.set("zeroing, please move away from the stage")
    #the z command zeros the motors for boundary business
    ser.write(b'z\r\n')
    
def run_program():
    """Runs the function Route and sets running to True (not a good start/stop system)"""
    #starts the program, but only after you zero the stage
    global running
    running = True
    varLabel.set("Program running")
    route()

def stop_program():
    """Sets the running flag to False and sends a stop command to the arduino"""
    #stops the program immediately
    global running
    running = False
    varLabel.set("Program stopped,please zero before continuing")
    #the s byte is a command that stops the stepper motors
    ser.write(b's\r\n')
    

if __name__== "__main__":
    root = tk.Tk()

    canvas1 = tk.Canvas(root, width=800, height=400)
    canvas1.pack()

    root.title('XY-stage controller')

    #instructions
    instructions = tk.Label(root,text='Enter the amount of hours you want your measurements to last in the text box.'
                            '\n Click on run program to start a measurement session.'
                            '\n Click on stop incase of an emergency or if it is wanted to stop the program.',
                            font = "Raleway")
                        
    instructions.pack(side='bottom')

    # initialize active labels
    varLabel = tk.IntVar()
    tkLabel = tk.Label(textvariable=varLabel,)
    tkLabel.pack(side='top')


    # Buttons for initializing a bunch of good functions

    zerobutton = tk.IntVar()
    tkrunprogram= tk.Button(
        root,
        text='Zero', 
        command = zeroing,
        height = 4,
        fg = "black",
        width = 10,
        bg = 'gray',
        bd = 5,
        activebackground = 'green'
        )
    tkrunprogram.pack(side='top')

    runprogbutton = tk.IntVar()
    tkrunprogram= tk.Button(
        root,
        text='Run Program', 
        command = run_program,
        height = 4,
        fg = "black",
        width = 10,
        bg = 'gray',
        bd = 5,
        activebackground = 'green'
        )
    tkrunprogram.pack(side='top')
    
    stopbutton = tk.IntVar()
    tkstopprog= tk.Button(
        root,
        text='Stop Program', 
        command = stop_program,
        height = 4,
        fg = "black",
        width = 10,
        bg = 'gray',
        bd = 5,
        activebackground = 'red'
        )
    tkstopprog.pack(side='top')

    Buttonquit = tk.IntVar()
    tkButtonQuit = tk.Button(
        root,
        text='Quit', 
        command = quit,
        height = 4,
        fg = "black",
        width = 10,
        bg = 'yellow',
        bd = 5
        )

    # initialize an entry box
    entry1 = tk.Entry(root)
    durbox = canvas1.create_window(400, 200, window=entry1)
    tkButtonQuit.pack(side='top')
    
    root.mainloop()

最后的 after 命令将引入 60 分钟的暂停，这将使程序冻结 60 分钟。希望有一个简单的解决方案来中断该功能！

提前谢谢你！

Answer 1

您可以使用多线程。在单独的线程中进行所有通信，并确保不要在子线程中更新 GUI 组件。

这是一个最小的例子：

import serial
import tkinter as tk
from threading import Thread
import time


def start():
    global running
    stop()
    btn.config(text="Stop", command=stop)
    running = True
    info_label["text"] = "Starting..."

    thread = Thread(target=run, daemon=True)
    thread.start()

def run():
    ser = serial.Serial("COM5", 115200, timeout=2)

    while running:
        ser.write(b'g115000\r\n')
        time.sleep(50)
        ser.write(b'g225000\r\n')
        time.sleep(30000)
        ser.write(b'g1400\r\n')
        time.sleep(50)
        ser.write(b'g2500\r\n')
    
    ser.write(b's\r\n')
    ser.close()

def stop():
    global running
    running = False
    info_label["text"] = "Stopped"
    btn.config(text="Start", command=start)


root = tk.Tk()
running = False

info_label = tk.Label(root, text="INFO:")
info_label.pack()

btn = tk.Button(root, text="Start", command=start)
btn.pack()

root.mainloop()

Answer 2

after(x000) 实际上与time.sleep(x) 相同 - 它使整个应用程序进入睡眠状态。作为一般经验法则，您永远不应该在与 GUI 相同的线程中执行此操作。然而，这并不意味着您需要使用线程。

tkinter 的after 方法让您可以安排命令在未来运行。如果您正在运行的命令很快，例如通过串行连接发送几个字节，那么这确实是您所需要的。与使用线程相比，它更简单，开销也更少。

例如，您的route 函数可能可以这样写：

def route():
    if running == True:
        # immediately write this:
        ser.write(b'g115000\r\n')

        # after 50ms, write this:
        root.after(50, ser.write, b'g225000')
 
        # after 30 more seconds, write this
        root.after(50+30000, ser.write, b'g1400\r\n')

        # and then after 50ms more, write this
        root.after(50+30000+50, ser.write, b'g2500\r\n')

        # and finally, after 12 seconds, do it all again
        root.after(50+30000+50+12000,route)

一旦你调用了这个，你就不需要再调用它，你也不需要在一个线程中调用它。它只是将一些工作放在一个队列中，这些工作将在未来的某个时间得到处理。

由于每次调用root.after都会返回一个id，你可以保存这些id，以便在想要停止一切的情况下，你可以在每个保存的id上调用after_cancel。

另一种方法是将作业定义为一系列延迟，然后是要写入的字节。例如：

job = (
    (0, b'g115000\r\n'),
    (50, b'g225000'),
    (30000, b'g1400\r\n'),
    (50, b'g2500\r\n'),
)

然后，您的 route 函数可能看起来像这样（未经测试，但这非常接近）

def route(job):
    global after_id
    delay = 0
    for (delta, data) in job:
        delay += delta
        root.after(delay, ser.write, data)
    delay += 12000
    root.after(delay, route, job)

该主题有很多变体。例如，您可以创建一个实现此逻辑的Job 类，或者job 可以包含命令而不是数据。重点是，您可以定义一个数据结构来定义要完成的工作，然后使用after 来安排该工作。