Hello there! I am designing a boom for load pickup, which also has to rotate. And one of the requirements is to reduce the speed of extension and rotation of the boom at the end of the ligting. What I mean by this. For the first 30 seconds, the boom has to lift at a speed of 0.3 m/s, and for the last 10 seconds, the lift speed has to be 0.03 m/s. I'm not very familiar with hydraulics, I'm just starting to learn it. So far I have realized that I need to use a hydraulic proportional valve and adjustable axial piston pump. I understand a little bit about l-s control when the pump changes pressure if the load on the boom changes. But I can't figure out how to forcibly change the boom extension speed when the boom load is unchanged. Could you please advise me in which direction to look and what equipment to pay attention to? And also how it can be organized. Thank you!
Good day If I interpret your post correctly you are trying to slow the boom speed towards the end of its stroke. I suggest this may be possible by draining the pilot line at a set point. You have mentioned rotation not sure which machine you have? Kind regards Uffex
Thanks for your reply! Intuitively, I also assume that it is necessary to reduce the pressure in the pilot line, but so far I have a vague idea of how to organize this and what equipment to use since the load does not change. Maybe you have articles or videos that well explain these operating principles and you can further study this information.
What machine are you trying to reverse engineer? Might give some insite on what your trying to do?
I don't know exactly the type or name (brand). This will be a machine for lifting the boom (weights) and rotating it. We are going to use Bosch or Danfoss equipment.
to get a positional change of rate, you need to "sense" position. This would be easiest to achieve with a magnet mounted on one part and a sensor coil on the other part. You could use a physical limit switch, but they are prone to getting contaminated and otherwise bent. Look at Cat loaders and the sensor and magnet. You can use more than one to smooth out the action.
Another method commonly used by many manufacturers is one or more position sensors whose signals act as inputs used to control an electro-hydraulic valve or valves.
Yes that is what I was getting to. he had not mentioned sensing position and needs to start there.
Could also use position sensors internal to the cylinders. That is a relatively new concept but much more common now than it was say 10 years ago.
Yes, exactly, I am going to use a cylinder with a position measurement system. I found this in Bosch. The problem is the next. I vaguely understood how L-S regulation works. The more weight we need to lift the more pressure we need and this L-S system adopts this pressure to the weight. But I need a little bit different - 2/3 of the length of the cylinder we lift the weight with the speed 0.3 m/s and the last 1/3 of the length - with the speed 0.03 m/s. So we must adopt (control/set) the flow rate and change it at the end of the operation (last 10 seconds). The external control system will get the length of the cylinder and the control system will open/switch to some valve or something. So here is the issue for me - how to regulate the flow rate?
What you describe as your requirement to control speed in different parts of the cylinder stroke requires a position-sensing input to a control valve, not load sensing. Load has nothing to do with controlling speed, they are two different parameters in the hydraulic system.
Yes, I understand the L-S regulation is not my case. I found that the flow rate can be changed by changing the number of revolutions of the electric motor of an axial piston pump or by installing a hydraulic throttle. It is also probably possible to change the pump flow rate by changing the angle of the plate in an axial piston pump, but how to do this?
In my opinion you are looking for an over-complicated solution to the speed issue. What you need is a position input to a electro-hydraulic control valve that reduces the oil flow to the cylinder(s) and as a result reduces the cylinder speed.
Most excavator hydraulic cylinders have hydraulic-mechanical cushions to slow down the speed of the hydraulic cylinder at the end of the stroke. Based on this working principle, we can also apply it here to reduce the speed of the hydraulic cylinder.
Thanks for your answer. I am wondering if this proportional flow control valve does not reduce the pressure and if can we use it with L-S regulation and a variable displacement pump?
It could be the solution I think, but what to do if we need to stop in the middle of the length? Could you please write a brand or what equipment is on the picture? I would like to read about it also.
as an example of using a Danfoss variable displacement pump You can refer to the attached file for more details.
Thank you for your answer! I will read the information!
I start thinking about this approach. because it can be a solution as well. If you look at the problem from the other side, one of the problems may be slowing down the boom when reaching the desired position. Not only at the end of the moving of the cylinder stroke but also in intermediate positions. Could you please suggest equipment for such purposes that would ensure high accuracy of boom lifting?
I don't see why you can't just slow it down by using the joy stick and feather it
The other way is using the proximity switch.
Thank you!
Are you making something military related?
No. It can be used anywhere where loads need to be lifted and moved. The main idea was to ensure the accuracy of the positioning of the weight. For example, to accurately move it into a window between containers, etc. The first thing that came to mind was to reduce the speed of lifting/lowering (and rotation) of the load. We are thinking of rebuilding the old crane and completely replacing the hydraulics with new ones.