06 March 2016

2.77 Seek And Geek #5: Hydraulic Cherry Picker

Seek And Geek #5: Hydraulic Cherry Picker

The other day I saw a Hydaulic Cherry Picker like the one above parked between Kresge and McCormick which had been used to put the "MIT 100 Years In Cambridge Celebration" posters up on Building 7.  

The whole thing has a telescopic arm made of square extrusion. I couldn't get a good peek inside of the mechanism it uses to actuate the telescoping mechanism, but considering everything else on this machine is hydraulic (which is good because there is only one power source that is distributed across the whole machine) I bet this is probably actuated hydraulically, with the piston motion amplified in some way through gearing or a linkage. 

Speaking of linkages, the whole thing has a "wrist" that's on a parallelogram 4-bar linkage, so it keeps the basket holding any operators parallel to the ground. 

 
A workspace analysis found online shows off just how much reach this thing has. The wrist allows fine positioning once the big arm has been extended. 

The big arm is actuated by a massive hydraulic piston in a 3-bar linkage. The forces it has to exert to hold the arm in place change given the angle of the arm, and the horizontal configuration requires it to bear the highest load. Luckily, static force holding is something inherently free in hydraulic systems!

 You can see the cable/hose carrier, bringing both electronic cables and hydraulic hoses up the arm to the the pistons located near the basket.

The wheels are hydraulic! Both drive and steering are achieved through hydraulic actuators. This thing is really slow when driving, no more than 15MPH, but at least no additional forms of power are needed. The same hydraulic power unit is used to move the arm, the basket, steer, and drive the wheels. 

There are two pistons that orient the basket! One is coupled to the 4-bar parallelogram linkage, and the other will simply change the angle of the entire basket with respect to the arm. This is probably coupled to the motion of the arm's beefy main piston near its base, so the basket is always oriented horizontally.

There also is a left-right rotational joint at the basket's wrist, also hydraulically actuated. 

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