1. Introduction Generally, machine tool spindle motor braking employs an energy-consumption braking method, where the motor receives DC power from both the AB phases. Using this method, stopping the spindle motor takes approximately 0.5 seconds at low speeds and approximately 2.5 seconds at high speeds. The current spindle motor braking method, as shown in Figure 1, involves first disconnecting switch KM1, then closing switch KM2 to disconnect the three-phase AC power and connect the DC power. After a 2.5-second delay, the spindle motor is considered to have stopped rotating before tool changing or other actions are performed. The time required to stop the spindle using energy-consumption braking varies depending on its rotation speed. Using the same energy-consumption braking time results in extended, unnecessary machining auxiliary time, reducing machine tool efficiency. Furthermore, if switch KM2 fails to close reliably, or if the DC power fuse trips and fails to provide DC power, the spindle motor can only decelerate under friction, requiring a long braking time. However, even after a 2.5-second delay, the machine tool's CNC system still considers the spindle motor to have stopped rotating. Performing tool changes or other actions at this time can easily lead to accidents. Therefore, we have improved the spindle braking control method. Instead of using a 2.5-second delay to determine if the spindle motor has stopped, we monitor the spindle rotation in real time. When the spindle speed drops below a certain threshold, a signal indicating that the spindle has stopped is immediately issued. 2. Spindle Speed ​​Monitoring Scheme A strip of iron is installed on the synchronous drive shaft of the motor, rotating synchronously with the motor. A proximity switch detects this strip, detecting two pulse signals per revolution. The speed is determined by detecting these pulse signals. There are two methods for detecting the pulse signals. The first approach: Count the number of pulse signals N within a certain period Tp. A PLC is a sequential controller; its program executes step-by-step from beginning to end. Each execution completes one scan cycle, and then the process repeats from the beginning. If the program has 2000 steps, with each step having an execution time of 30μs, the scan cycle is approximately 60ms, and the scan frequency is approximately 16Hz. The accurately detectable pulse frequency should be below 8Hz. When the pulse frequency of the rotational speed is greater than 16Hz (i.e., n≥480r/min), the PLC, affected by its scan frequency, cannot accurately detect the number of pulses. In severe cases, at high speeds, very few pulses may be detected, leading to a misjudgment that the motor has essentially stopped and subsequent actions are performed, causing an accident. This approach is only suitable for monitoring the low-speed rotation of the spindle. The second approach: Detect the duration T of the pulse signal being continuously "0" or "1". When n<60r/min, issue a signal indicating that the spindle has stopped. Due to the delay in PLC program execution, by the time the CNC system receives the spindle stop signal and executes the following actions, the spindle has already completely stopped rotating. The pulse signal corresponding to n=60r/min remains "0" or "1" for 0.25s. Therefore, we set the timer for detecting the pulse signal to 0.25s. Similarly, at high speeds, inaccurate pulse measurement may occur, but regardless of the severity, "0" or "1" will change at least once within 0.25s, thus accurately determining whether the spindle has stopped rotating. This scheme can be applied to the detection of spindle braking status during high-speed or low-speed spindle rotation. In practical applications, we adopted this scheme. 3. PLC Implementation of Spindle Energy Consumption Braking Control Method In the PLC design program, X20.0 is the input of the speed pulse signal, M05 is the spindle stop signal, and Y50.0 is the spindle stop completion signal. Two timers, TM1 and TM2, determine whether the X20.0 pulse signal has been continuously "0" or "1" for a set time. Once either timer reaches its set time (i.e., R100.1 or R100.2 becomes "1"), causing R100.3 to become "1". At this point, M05 becomes "1", causing Y50.0 to output "1", thus issuing a signal that the spindle braking is complete, achieving accurate determination of spindle stop. 4. Conclusion Our improved control method using a PLC to control the machine tool spindle braking reliably determines the spindle's rotation state, avoids machine tool malfunctions, saves auxiliary time for spindle machining, and further improves the machine tool's protection performance.