Motor and Gearing Type for High Torque Cam Application

[TimAK]

I am currently undertaking a project to upgrade a fork lift. The requested task is to change the hydraulic tilt mechanism used to tilt the fork lift to an electrically powered system that enables precise position control.

So far I have narrowed a solution down to using some form of electric motor (to be defined) with a CAM shaft. The required movement is to tilt the fork carriage from -2degrees to +2degrees and output position.

The system is configured with the carriage hung from a pivot, the current hydraulic system pushes the carriage at a vertical position 270mm below this pivot and the worst case scenario for loading is a load of 2666 Kg loaded on the forks at a horizontal position of 1270mm from the pivot.

I have calculated that the moment about the pivot due to the load applied to be 33140 Nm and therefore the force pushing horizontally from the current hydraulic system, and therefore required by the new electrical system, to be 132031.9 N

Could anyone suggest how to go about sizing a suitable motor and gearing system for this application and if it is feasible to use a cam to move the carriage?

The alternative to a cam is to use a dog bone rod to connect the carriage to the shaft and have the shaft only rotate by 90degrees in order to achieve the motion.

Thanks

 

[MikeHalloran]

Or, you could replace the hydraulic cylinder with an electric linear actuator capable of ~15 tons of force. Maybe someone has one on the shelf. Maybe it will have to be a custom unit, but it should be do-able. Such devices typically use screws or roller screws or something similar, but not cams.

Cams are tricky because of the input torque, the radial load, the point load at the follower surface, the lateral reactions on the follower, and all the other maddening details that must be considered. Most engineers don't design cams often enough to remember all that stuff, so chances are you'll get to do it over at least once.





Mike Halloran
Pembroke Pines, FL, USA

 

[SceneryDriver]

With a properly (re)engineered hydraulic system, you should be able to get the required position-ability. How will you power the electric motor generating that much force? Is the forklift electrically (battery) powered, or engine-driven? You may have a hard time generating the required electrical power if the forklift is engine driven.

Post a link to this thread in the Fluid Power forum:

http://www.eng-tips.com/threadminder.cfm?pid=1083

Peter Nachtwey will hopefully comment with some helpful suggestions.


-SceneryDriver

 

[mikekilroy]

33000nm is only part of required spec; what speed is required? need that to have any clue what size motor is required.

 

[LionelHutz]

I'd think a gear box, possibly including a worm drive, with a crank on the output and a connecting rod to the carrage before I'd look at a cam with a follower running over the surface.

You need to figure out how you are going to keep it stationary without constantly driving the motor at 0 speed to hold it stationary.

Why not investigate better hydraulic controls?

 

[ScottyUK]

This should be achievable using a hydraulics only: we could move the actuators for our turbine governor valves in steps of one thou using electro-hydraulic control. The downside of this type of control is that the servo valves are relatively expensive and the oil has to be very clean, but the capability is there. As noted above, Peter Nachtwey over in fluid power engineering is something of a guru on these things.