Trends Seen from Trade Shows

[PNachtwey]

I was in China last week at a small trade show focused on metal industries. Voith made a presentation about controlling hydraulic actuators directly with pumps with out valves. Several different options were presented. The simplest and probably the best they called a CLDP or closed loop differential pump where one motor ( VFD or servo ) controlled two pumps. Each pump is sized in proportion to the surface areas on the cap and rod side of the piston. The position control seemed to be poor though as shown by the Voith graphs. The Voith position control only look good when compared to some other system that was worse. A Chinese professor told me it was because the pumps become inefficient at low flow. It seems to me these hybrid actuators competes more with the Exlar type of electric actuators only it uses hydraulics instead of gears to convert rotational to linear motion. Energy costs must be high to justify the extra cost to get a pay back.

I was at a small trade show in the US. Finally people are talking about servo pumps here. Although I know there have been a few people that have done servo pump control in the last 10 to 12 years it is hard to convince people to put the extra effort into making such a system. Few want to even put a pressure transducer on the output of the pump in an effort to keep the pressure constant without the use of a big accumulator. Few ( <1% ) want to use the instantaneous calculated flow requirements from the motion controller to provide a feed forward control to the pump so the pressure doesn't need to drop. Some assembly is required. Pumps are not equally efficient over the whole range of flows. Some programming is needed to optimize efficiency.

I have known how do to this for years. I/we don't integrate systems and it has been ALMOST impossible to get others to try these advanced techniques.


Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

http://forum.deltamotion.com/

 

[MikeHalloran]

I love advanced stuff, but many hydraulic systems are maintained by people who can break a solid steel ball with no tools.



Mike Halloran
Pembroke Pines, FL, USA

 

[PNachtwey]

In China I sat across a Chinese man at dinner that told me he thinks the US is behind China and Europe. Perhaps our electric power is so cheap it doesn't justify the extra cost but a lack of training/education is not a good reason.

Behind is not good. It is hard to compete from behind.




Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

http://forum.deltamotion.com/

 

[bcd]

Or is the reward so little it is not worth taking the risk over proven technology?

 

[IceStationZebra]

What kind of reaction time would one expect from a 50-70gpm servo pump set-up? ISZ

 

[PNachtwey]

What kind of reaction time would one expect from a 50-70gpm servo pump set-up? ISZ

I am sure it depends on how expensive the servo motor and controls are. The problem is that servo motors that size are expensive. People usually use a VFD at the larger size but then VFDs don't work so well at low speeds. From what I saw the larger system use VFD and controlled the swash plate. There are optimal combinations of VFD speed and swash plate angles for different flow requirements. These solutions are perfect but they are better.

When I was at a MSOE seminar 4 years ago I talked to one of the professors about how fast the motor can respond. He indicated that it can be quite quickly but there is a limitation if the motor/pump combination is just sucking oil out of the tank. There must be enough net positive suction head, NPSH, to avoid cavitation or the motor must be limited so it doesn't accelerate too quickly.

The Voith CLDP ( closed loop differential pump ) has this problem licked because the accumulator is also the tank or oil reserve so the intake of the pump always has enough pressure.


Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

http://forum.deltamotion.com/