Hello Everyone
I chose this as home mode,
mchoming_absolide_swich. pAxMARM_Par.Home.Start Direction(sensor search direction)
Switch Edge (sensor triggering status)
What is Homing Direction, what does it do?
Is it the direction change status when the sensor is triggered?
Hello,
The Automation Studio help descripes the 4 different Movement Variants on the right side. On the left side it is shown which Parameter combination leads to this movement.
So you have to coose your required movement, mostly i think by the Endposition displayed by " —| ".
As the text in the blue box states, the “start direction” is ignored by this mode, as the direction is calculated by the level of the Homing Switch at the Start Position.
Greetings
Michael
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Switch Edge:= negative;
Homing Direction:= whether negative or positive;
servo is looking for sensor (negative direction) and sensor is 0-1.
When Homing Direction is negative, in variant 1, when sensor passes 0-1, it changes direction again, here it passes 1-0, sensor finishes negative triggering and stops again after passing 0-1?
When Homing Direction is positive, in variant 2, sensor passes 0-1 and again passes 1-0, here sensor finishes negative triggering and stops.
In case 1, why does witch Edge change direction again and see sensor again even though negative triggering is completed? What is Homing Direction used for?
Hello,
with the First seen Event of the Sensor, the Axis switches from “search” velocity to “trigger/homing” velocity. To ensure that allways the same trigger event is used we have to move back and then go again over the sensor.
Sensors can have a hysteresis. Combined with the velocity of the axis this could result in an error which you want to keep small, thats why the Trigger Velocity should be small.
But a small Velocity could leed in a very long search time, thats why there is an faster search speed implemented. Ans this is why it, in some cases turns around more often.
Greetings
Michael
2 Likes
Hello, in the 1st variant the sensor makes 3 states, first it makes 0-1, then it makes 1-0 and then it makes 0-1, when Switch Edge:= is negative it passes 0-1 in the last state, normally it should stop when it passes 1-0, right? In the 2nd variant there are 2 states, the sensor first passes 0-1, then passes 1-0 and stops, so the sensor stops in negative triggering.
In Variant 1, when the Switch Edge is negative, the sensor is positive in stop . In Variant 3, when the Switch Edge is positive, it is negative in stop. When the Switch Edge is negative, it is negative. When the Switch Edge is positive, it is positive. Why is this not the case?
Hello,
I don’t get your issue … you have 2 Prameters to select 4 Variants.
So all possible combinations are used.
SwitchEdge Defines wheter you have the fist 2 Pictures, or the second 2 Pictures
The first 2 Pictures for Negative have a common TURE on the negative movement Side.
The second 2 Pictures for Positive have a common FALSE on the negative movement Side.
The HomingDirection shows if the movement Ends on the Positive movement Side or on the negative.
0 0
0 1
1 0
1 1
Greetings
Michael
1 Like
Thanks but I didn’t understand something. If I were to write my question in more detail, it is as follows. In Variant 1, the Key Edge is negative, so when it finds the negative direction, it should complete the homing process, but when it goes from the negative direction to the positive, it completes it, I didn’t understand this
Hello,
Is this just a theoretical issue/understanding topic or do you have a real axis missbehaving?
The documentation shows the correct behaviour.
These are the selectors and their meaning.
Greetings
Michael
1 Like
If it helps you can think of this mode as working in this sequence.
- If sensor is on, go to Step 3, else (Sensor Off) go to step 2.
- Start movement at Start Velocity in the direction of Switch Edge. If Sensor found (0->1), go to Step 3.
- Move off of sensor at Trigger Velocity. If Sensor is off, go to Step 4.
- Move back towards sensor at Trigger Velocity. Record home position on 0->1 transition.
Switch Direction (edge_sw) → Direction of axis movement to find sensor
Trigger Direction (trigg_dir) → Direction of axis movement to detect edge of sensor
Start Velocity (v_switch) → Speed we look to find the sensor
Trigger Velocity (v_trigger) → Speed we move once sensor is located
The axis will always move in both directions no matter what to find the correct edge to reference against.
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When the servo was going in the positive direction, the Switch Edge went from the rising edge to the falling edge (1>0) and if the Homing Direction was positive, the direction was positive when the sensor was on the falling edge. Here it had to complete the process, why did it come from the falling edge to the rising edge again (0>1) and then from the rising edge to the falling edge (1>0) to complete the home position process in the positive direction. Why did it do the same steps when it should have completed in the first step?
The multitude of homing routines with the ACOPOS system are designed to provide accurate and precise referencing modes. They don’t prioritize time efficiency.
As I said previously, in the mode you are choosing, using Absolute Switch, the axis will always move in both directions, and may move in one of them again. This is due to the search speed and trigger speed within this modes design and the desire for maximum precision.
The switch/trigger inputs on the ACOPOS drives have an accuracy between 1 and 50 us. So depending on your searching speed you can have a large margin when trying to reproduce your referencing routines accuracy. A slow trigger speed ensures a high precision of measurement. However if your distance of travel for referencing may be potentially meters long, a slow trigger speed may cause your referencing to take an extremely long time.
If you want to move to one of the ends of the axis travel and find a limit switch on the end, perhaps you should check out the mcHOME_LIMIT_SWITCH mode. If the Fix direction mode is set, the axis will only move in the direction of the limit switch you’ve chosen and will stop when finding it. I.e. what you seem to indicate you want to happen. mcHOME_ABS_SWITCH will always move at least two directions to make sure there is no hysteresis / slop in the sensor edge detection and to ensure it’s detecting the correct transition.
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Hello,
Thanks Matt Buck for the very good description. But there is one point i want to add… mcHOME_ABS_SWITCH can be configured to not turn around if this is the requested need. You only have to read the level of the switch before starting to home and set the parameter in a correct way.
The pictues are the best way to descripe whats happening, because i think i would still not be able to understand the textual description from RHYS above, so thanks for adding that picture it helped me to understand that you simply don’t want to turn.
Greetings
Michael
1 Like
I’m just trying to understand.
Is the StartDirection irrelevant for sensor search direction?
Do we determine the sensor search direction based on the SwitchEdge setting?
(For example:
If SwitchEdge := positive, does it mean the sensor will be searched in the positive direction?
If SwitchEdge := negative, does it mean the sensor will be searched in the negative direction?)
If we determine the sensor search direction based on the SwitchEdge,
then when I want the homing to happen on either the rising edge or falling edge of the sensor signal,
where do I set the sensor trigger?
Hello,
Is the StartDirection irrelevant for sensor search direction?
Do we determine the sensor search direction based on the SwitchEdge setting?
Please just read the Documentation before asking… its written there.
And just make sure you don’t need “mcHOMING_SWITCH_GATE” if your desired movent is still not in the pictures.
Greetings
Michael
2 Likes