The Excavator Hydraulic Jack Forces are Changing Direction in Simscape Multibody

4 次查看（过去 30 天）
Medalan
Medalan 2024-6-15
回答： Yifeng Tang 2024-6-24
I am trying to model a mechanism of excavators in the Simscape multibody.
I am using prismatic joint to simulate the functionality of hydraulic jacks with the following settings:
I motion the hydraulic jacks (using PS Ramp bock) and track the sensed "actuator force" parameter via a scope block.
So technically, I am doing an Inverse dynamic analysis to calculate the needed force on the hydraulic jacks and because during my simulation, all of the jacks (modeled with Prismatic joints) are getting opened, I am expecting that all the actuator forces be positive; however, the sign of force is changing over the simulation (!) which I believe it is wrong as I set to the motion of prismatic joints in one direction and the actuator force should be along this direction too. So I was wondering, why this is happening?!
  3 个评论
显示 1更早的评论
Medalan
Medalan 2024-6-23
Hi @Yifeng Tang
Thank you for the comment and also my apologies for the delay.
Actually, I think You somehow mentioned the right reason. I checked the model and I noticed one thing. In "inverse dynamics," the inputs are "q," "dq," and "ddq," and the derivation of "dq" and "ddq" is automatically performed in the "PS Ramp" block. So, in my case, the motion is constant velocity. In this scenario, the prismatic joint should sometimes apply a negative force to prevent increased speed.
I think this is the main reason I had negative force; However, it also shows that this strategy is just suitable for static analysis. For an accurate simulation, I have to use the hydraulic blocks and directly feed the prismatic joint with force, instead of motion.

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Yifeng Tang
Yifeng Tang 2024-6-24
The way the joints are actuated and the joint forces are sensed for inverse dynamic analysis looks OK.
As a position signal is used as the actuation signal, it's 1st & 2nd order derivatives (velocity and acceleration) are also implied. In this particular case, the position changes linearly, so the velocity remains constant and the acceleration is zero. This requires that all forces sum to zero at the joint. As the mechanism moves, the sum of the gravity force may drive the mechanism to move on its own and the hydraulic force may be negative to enforce the zero acceleration we provided as actuation signal.

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Assembly 的更多信息

标签

产品


版本

R2020b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by