Before performing servo positioning operations, it is generally necessary to perform origin return first; otherwise, the servo motor will not work properly and will alarm with the message "Starting before origin return is completed".
So, why perform origin regression? And how is origin regression performed?
Origin return of servo motion control
I. The Necessity of Origin Regression
1. Positioning means moving the servo motor to a specific location.
2. This position can be incremental or absolute. For example, if we are on the road and we need to move forward 10 meters, it means our position needs to increase by 10 meters. This 10 meters is a position increment.
3. If we want to go to a coffee shop somewhere on this street, we need to know its exact address. Let's assume that the address of this street is not a house number, but rather 0 meters from one end of the street (the base position). This way, we can determine the address of every location on this street. For example, if the address of this coffee shop is 100 meters away on this street, then this 100 meters is an absolute location. No matter where we are, we can find this coffee shop by walking 100 meters away on this street.
4. In the positioning instructions, there are two types: incremental INC instructions and absolute ABS instructions.
5. Incremental (INC) method
Starting from the current stopping position, specify the direction and amount of movement before positioning.
6. Absolute Value (ABS) Method
Locate the specified address, which is a position relative to the origin.
7. Therefore, when we need to perform absolute positioning, we need the corresponding mechanical system to have an address, which requires a reference position. This reference position is used to determine the address of each position on the mechanical system. In a servo positioning system, this reference position is called the origin.
II. Two signals
1. In Mitsubishi's servo positioning system, there are two key signals regarding the origin:
2. Origin Regression Request Signal (Origin Reset Request Flag)
When this signal is ON, it indicates that the servo system currently has no origin and needs to perform origin regression.
3. Origin return completion signal (origin reset completion flag)
This signal will be ON when the home return process is complete. Then, if the servo motor leaves the home position during positioning or other normal operations, this signal will be OFF, but the home position will still exist.
4. To determine whether origin regression is needed, the origin regression request signal should be used, rather than the origin regression completion signal.
For incremental systems, a return to the origin is required after each power outage reset and power-on.
5. For absolute positioning systems, since the servo amplifier is equipped with a battery (and also needs to be set to use an absolute position system in the parameters), it can maintain the position of the servo motor. Therefore, under normal circumstances, only one origin return is needed when the system is first set up. Of course, if the origin position is lost later, the origin return will need to be performed again. Whether origin return is needed can also be determined by whether the origin return request signal is ON.
III. Common Origin Regression Methods
1 Data setting type
This method sets the current position as the origin. Therefore, regardless of where the servo motor is currently stationary, as long as a data-defined origin return is performed, the current position will become the origin. Thus, in this method of origin return operation, the servo motor will not move!
2. This method can be used when the servo does not need to perform absolute positioning, such as when it only needs speed control, torque control, or incremental positioning.
3. In the servo parameters, the default setting for the origin is "needs to pass through the Z phase of the servo motor after power-on". Therefore, when performing this type of data-setting origin return, you must either set this parameter to "does not need to pass through the Z phase of the servo motor after power-on", or first perform JOG to make the servo motor rotate more than one revolution before performing origin return.
4 Near-point DOG type
▼What is a near-point DOG?
The near-point DOG is actually a sensor signal. We need to determine the origin position, so how do we do that? Do we use JOG to rotate the servo motor, visually observe it until it reaches the desired position, and then perform a data-driven origin regression? This would obviously be very inaccurate.
5. So, could we do this: add a marker at the location we want to define as the origin, and then stop the servo motor when it reaches that marker, thus defining the servo motor's current position as the origin? Of course!
6 Therefore, the near-point DOG signal is such a marker.
