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Use of Linear Stepper Motors in the Control of Roller Engine Speed Author: Li Heqing, Sany Heavy Industry Road Machinery Research Institute Source: Design Innovation. A fully hydraulic double-drum roller is a construction device used in modern road construction to compact the pavement so that it meets the desired levels of density and smoothness. Since a road roller primarily operates by means of its movement and vibration, its traveling speed and excitation force determine the quality of the construction. As the engine that provides the driving force, its operating condition and efficiency directly affect the overall performance and lifespan of the roller ； Its operating speed directly affects the overall output power of the machine. To improve the overall performance and efficiency of the roller, as well as to make the most of the engine’s ability for continuous speed regulation, we achieve these goals by implementing closed-loop control over the engine speed in order to automatically adjust it. During normal operation, a double-drum roller is in three different states: static rolling movement, vibratory movement, and high-speed movement while changing locations. These three states require different power outputs from the engine. The signals from the control lever, gear switch, and vibration switch are fed into the PLC; through logical relationships between these signals, the appropriate engine speed can be determined. Additionally, the PLC receives pulse signals from the speed sensor located on the engine’s flywheel housing. Both sets of signals are sent to the PLC’s PID regulator, which, after performing certain calculations, outputs high-speed pulse signals and direction signals to the driver. The driver then converts these signals into two sets of drive pulses with a 180° phase difference, which are sent to the linear stepper motor. The motor rotates by a certain angle, causing the spline shaft to move linearly in the corresponding direction, thereby moving the engine’s throttle lever to the exact desired position. This ensures that the engine operates at the specified speed, thus achieving an optimal match between the engine’s power output and the required power demand. Currently, the drive devices used in electronically controlled throttle systems on the market include linear proportional solenoids, swing stepper motors, and linear stepper motors. A comparative analysis is as follows: Linear proportional solenoids: They have a simple structure, require no maintenance, offer high reliability, respond quickly, and enable precise control of displacement. They are controlled using PWM pulse signals with a low pulse frequency of 500 Hz; moreover, they must be equipped with overload protection mechanisms at their limit positions. Based on the above analysis, we ultimately chose linear stepper motors. By improving the accuracy of installation fit, implementing high-idle speed limit protection and software-based protection mechanisms, not only is precise control of constant speed achieved with a control accuracy of ±20 RPM, but the service life is also increased; as a result, the products have been able to operate for 1,000 hours without any failures. During the operation of the YZC12 II fully hydraulic double-drum roller, if there is a sudden change in load and the engine speed exceeds or falls below the allowable operating range, it may cause severe damage to the equipment. Therefore, it is necessary to employ various methods for soft speed limitation as a form of protection, as well as mechanical speed limits as a form of hard protection. During the engine speed-up and speed regulation process, the real-time speed value is fed back to the PLC, which then performs high-speed counting; the stepper motor rotates in the forward direction, causing the high-speed counter to increase its count ； When the stepper motor rotates in reverse, the high-speed counter counts downward. The PLC automatically analyzes the number of steps taken by the stepper motor during normal operation of the engine, and performs calculations to determine the maximum number of steps the stepper motor is allowed to take in forward rotation. If, for some unexpected reason, the engine’s speed rises to its maximum level, the PLC automatically shuts down the stepper motor to prevent the diesel engine from exceeding the permitted maximum speed ； If the engine throttle is already at full opening and the speed value is still below the set value, the PID will become unbalanced; at this point the limit switch activates, shutting off the high-speed pulse output, the PID is reset, and the stepper motor stops working. We have applied the above control technologies to both fully hydraulic double-drum rollers and fully hydraulic rubber-tired rollers, achieving excellent results: first, remote control and automated operation can be easily implemented, which reduces the workload on operators; moreover, the layout of the control panel is simpler and more aesthetically pleasing ； Second, the engine can automatically adjust to different speeds under varying loads, achieving the optimal match between load and power and reducing fuel consumption ； Third, the engine can operate stably at low idle speeds, avoiding the resonance zone of the entire machine, thereby reducing vibration noise and emission pollution at low speeds. By using this control device, not only is the operating efficiency of the engine improved, but the reliability and operability of the entire system are also enhanced, allowing its advantages to be fully utilized; as a result, it has received high praise from users everywhere.