Theory of controllable acceleration

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Theory of controllable acceleration

Postby mars_bruce_lee » Mon Dec 10, 2018 7:23 am

Servo valve model: D662-D01HDAM6VSX2-A/D662-4223
Response time 0~100% Step signal: 44ms
100% Stroke Corresponding speed:1000mm/s

Maximum acceleration that the valve can achieve a=v/t=1000/0.044=22727mm/s2
Controlled acceleration is definitely not achieved due to the positioning。

Regardless of mechanical and electrical considerations, from hydraulic considerations,In this case, how should the theoretically controllable acceleration be calculated.
What is the relationship with the theoretical maximum acceleration?
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Re: Theory of controllable acceleration

Postby mars_bruce_lee » Mon Dec 10, 2018 7:46 am

uses ±10% positive overlap servo valve,In high-speed reciprocating motion, overlap will definitely affect the response time of the valve.
How to consider this impact in your application
Did the following test,After the voltage is given, the cylinder will only start to operate after 18ms.
Whether this delay time is caused mainly by overlap or other factors
Attachments
test.rmcplots
Acceleration test curve
(3.54 MiB) Downloaded 2 times
截图08.png
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Re: Theory of controllable acceleration

Postby Peter Nachtwey » Mon Dec 10, 2018 4:12 pm

A valve with 10% overlap is not a true servo valve. A valve with 10% overlap may work for constant velocity applications but not for systems that must accelerate and decelerate.
I can see by the plot that there is also a very large dead time in the valve. It takes many milliseconds to even start to move. The damping factor is also very low. This makes control difficult without using a good valve.

Yes, there is a limitation on how fast the actuator should be told to accelerate. The frequency of acceleration should be about 1/4 of the natural frequency of the cylinder and load. I have posted articles about this on iyeya.cn.

You really are hurting yourself by using poor valves. I know better valves will cost more but they will pay for themselves in easy of optimizing the system and performance.
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Re: Theory of controllable acceleration

Postby mars_bruce_lee » Mon Dec 10, 2018 6:52 pm

Peter Nachtwey wrote:A valve with 10% overlap is not a true servo valve. A valve with 10% overlap may work for constant velocity applications but not for systems that must accelerate and decelerate.
I can see by the plot that there is also a very large dead time in the valve. It takes many milliseconds to even start to move. The damping factor is also very low. This makes control difficult without using a good valve.

Yes, there is a limitation on how fast the actuator should be told to accelerate. The frequency of acceleration should be about 1/4 of the natural frequency of the cylinder and load. I have posted articles about this on iyeya.cn.

You really are hurting yourself by using poor valves. I know better valves will cost more but they will pay for themselves in easy of optimizing the system and performance.



Thanks

Can you share the englishoriginal article.
How to calculate natural frequency of the cylinder and load?
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Re: Theory of controllable acceleration

Postby mars_bruce_lee » Mon Dec 10, 2018 6:54 pm

Servo valve model: D662-D01HDAM6VSX2-A/D662-4223
Response time 0~100% Step signal: 44ms
100% Stroke Corresponding speed:1000mm/s

Maximum acceleration that the valve can achieve a=v/t=1000/0.044=22727mm/s2


Is it simple to think so?
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Posts: 210
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Re: Theory of controllable acceleration

Postby Jacob Paso » Mon Dec 10, 2018 8:38 pm

Only for a very light load. Acceleration depends on the force and mass: F=m*a.
On a hydraulic system, you need to account for the pressure drop across the valve. The remaining pressure is available to accelerate the load. It will also compress oil. Hopefully, the valve is on the cylinder so there won't be much oil to compress or hose to expand. With the remaining pressure, the cylinder area determines the force applied to the mass, which will give the acceleration.
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Re: Theory of controllable acceleration

Postby mars_bruce_lee » Tue Dec 11, 2018 1:03 am

Give the valve a step signal, the actual speed signal is shown below
By calculation, the maximum acceleration of the limit is 11000.
Is this value helpful for choosing the right acceleration?
Attachments
截图13.png
截图13.png (88.91 KiB) Viewed 95 times
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Re: Theory of controllable acceleration

Postby Jacob Paso » Tue Dec 11, 2018 5:07 pm

Assuming the load is the same now as what it will be during normal operation, then yes, a step jump will show what the maximum acceleration from a stop is. The step jump must be 0-100%.
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