I. Initial program execution.
When the program is run for the first time, although the current position may be 0 and there is an origin signal input, the system does not know where the origin signal is. To perform absolute positioning, the origin signal must be found in a specific way using the return-to-origin command, which is the true origin.
Second, after multiple positioning attempts, in order to eliminate errors, it is necessary to return to the origin.
Stepper systems use open-loop control, which makes them prone to missed steps or overstepping during movement, resulting in errors. The mechanical backlash itself also contributes to these errors. After repeated positioning, the accumulated errors become increasingly large, making the positioning accuracy unacceptable. Therefore, a homing operation is necessary. While servo systems use closed-loop control and do not experience missed or overstepping steps, interference from the pulses transmitted from the PLC to the servo drive circuitry, along with errors caused by mechanical backlash, can still affect positioning accuracy. Therefore, a homing operation is also required after a period of time.
3. If the location changes or is lost after a power outage, it is necessary to return to the original point.
Stepper motors do not have encoders, while servo motors typically use incremental encoders. These encoders cannot detect position changes after a power outage. Therefore, if the position changes due to human intervention, gravity, or inertia after the power is cut off, the PLC can no longer accurately determine the current position. To ensure positioning accuracy, a homing operation is required. If the motor's position did not change after a power outage, or if the motor has an absolute encoder, is a homing operation still necessary upon power-on? Although incremental encoders cannot recognize the position after a power outage, the current position can be stored in the PLC's power-off retention memory before the power outage. Even after a power outage, the current position will not be lost, and a homing operation is not needed upon power-on. Absolute encoders, even if they rotated after a power outage, can automatically recognize the current position upon power-on, so a homing operation is not necessary. However, it is worth noting that absolute encoders are divided into single-turn and multi-turn types. The position rotated after a power outage must be within the recognizable range; otherwise, a homing operation is required.
Fourth, performing operations such as reset clears the current position.
When a program malfunctions, in order to restart, we need to perform a reset operation to reset all states, including the current position, to their initial state. This requires us to perform a return-to-origin operation.
The above describes four scenarios for returning to the origin. This only represents my personal understanding of returning to the origin, and there may be other situations where returning to the origin is necessary. Discussion and exchange are welcome.
Disclaimer: This article is a reprint. If it involves copyright issues, please contact us promptly for deletion (QQ: 2737591964). We apologize for any inconvenience.
