Use Multibody Spool component with only pulling force (can't push)

I have a Simscape Multibody model that uses a hydraulic winch to control the extension and retraction of a level arm. When extending, I want the hydraulic winch system to control the overrunning load (motor operates as a pump that generates hydraulic pressure). However, I am seeing instead that the model is pushing the level arm.

Is there a way that the spool component can only behave like a rope and only apply pull forces? Or should I be going about this modeling in a different way?

Answer 1

[Simar]

Hi Jeremy,

As per my understanding you want to adjust the Simscape Multibody model to ensure the hydraulic winch's spool component only exerts pull forces, like a rope, to extend a lever arm without pushing it.

Directly simulating a spool component that behaves like a rope, applying only pull forces and not push forces, requires a specific approach since Simscape Multibody components inherently react to the forces and torques applied to them based on the physical laws governing the system. Following are approaches to achieve the desired behaviour:

Approach 1: Use of Simscape Forces and Motion Blocks

Utilizing Simscape Foundation Library’s Translational Spring and Damper blocks or Rotational Spring and Damper blocks, depending on setup. These components can simulate the tension (pull force) in a rope. Adjust the spring constant to a low or negligible value and use damper to simulate hydraulic resistance. This, however, does not directly simulate the spool as a rope but can be used to create a force that only acts in tension, not compression.

• Translational Damper- https://www.mathworks.com/help/simscape/ref/translationaldamper.html?searchHighlight=Translational%20Spring%20and%20Damper%20blocks%20&s_tid=srchtitle_support_results_1_Translational%20Spring%20and%20Damper%20blocks%20
• Rotational Spring- https://www.mathworks.com/help/simscape/ref/rotationalspring.html?searchHighlight=Rotational%20Spring&s_tid=srchtitle_support_results_1_Rotational%20Spring

Approach 2: Hydraulic System Modelling

Since application involves a hydraulic winch, consider modelling the hydraulic circuit using Simscape Fluids. This would allow to accurately model the behaviour of hydraulic winch, including the transition between operating as a motor and operating as a pump. Use hydraulic cylinders in Simscape Fluids to represent the action of the winch cable. By correctly setting up the hydraulic circuit, can ensure that hydraulic pressure only extends the lever arm and does not push it when retracting.

• Simscape Fluids- https://www.mathworks.com/help/hydro/index.html?searchHighlight=Simscape%20Fluids&s_tid=srchtitle_support_results_1_Simscape%20Fluids
• Hydraulic Cylinder- https://www.mathworks.com/help/simulink/slref/single-hydraulic-cylinder-simulation.html?searchHighlight=hydraulic%20cylinders&s_tid=srchtitle_support_results_1_hydraulic%20cylinders

Approach 3: Clutch Mechanism

Implement a clutch mechanism in the model that disengages connection between winch and the lever arm when winch would otherwise push the lever arm. This can be done using the Clutches components in Simscape Driveline. When the winch operates in the overrun condition (acting as a pump), the clutch disengages, preventing any pushing force from being applied to the lever arm.

• Clutches- https://www.mathworks.com/help/sdl/clutches.html?searchHighlight=Clutches%20and%20Brakes&s_tid=srchtitle_support_results_2_Clutches%20and%20Brakes
• Simscape Driveline- https://www.mathworks.com/help/sdl/index.html?searchHighlight=simscape%20Drivelines&s_tid=srchtitle_support_results_1_simscape%20Drivelines

Recommendations: Given specific description of wanting the winch to act as a pump during overrun, recommend focusing on accurately modelling the hydraulic system using Simscape Fluids. This approach will give the most realistic simulation of system's behaviour.

Hope it helps!

Best Regards,

Simar