Knee design for a robot 1

[robotdesigner]

I'm trying to design a robot which is similar to that of a human leg. The leg of the robot must be able to lift at least a ton and the knee of the robot must be able to bend to the same range than that of a human leg. Unfortunately I don't have much experience in mecanical engineering.

I tried to design the knee by joining the upper leg and lower leg at a common axis of rotation through an axel. Unfortunatly, after a small amount of bending both legs collide into each other limiting the range of rotation of the leg. It is possible to modify one or both parts of the leg to enable a bit more range of rotation, but this makes the structure of the leg weaker.

I thought of another design that would enable a very large range of rotation. I modeled the knee of the robot in a similar way than that of a human knee. In a human knee, one bone is in contact with the other and rotates around it. The bones are held together through ligaments. Similarly, the common extremity of the upper leg and lower leg of the robot are made as a gear (each gear is spanning 180 degrees only). The gears are maintained at a very close but fixed distance from each other through a metal frame (in the center of each gear, there is an axel where the frame is attached. Hence there are two axels in this design while in the previous design there was only one). A cable is connected at the front and a second cable is connected to the back of the leg (on the upper and lower leg)would enable the leg to be bent. In such a way the leg could bend as much as needed.

However, I have many questions on the subject. In such a configuration, does the gears need to be lubricated? Is lubrication crucial? How much would the lifespan of the gears would be reduced if I don't lubricate?

In practice, I haven't seen this latter design anywhere. It seems robust and very flexible. Is there any important reason why this design is not good? Is this design too complex? Is it flawed? Too costly? Would there be too much stress applied on the gears?

Any information on any of those questions would be greately appreciated.

 

[Matt51]

Your proposed design is feasible. The gear loads would be relatively high. Properly designed non-involute gears greatly reduce the need for lubrication. There are a range of material options, including coatings, surface treatments, and dry film lubricants, that will allow your application to work without grease or oil. Allowable tooth contact stresses must be reduced substantially compared to oil lubricated gears.
You may want to consult a patent attorney before you continue writing on this subject. It appears to me you may have a patentable design, hopefully what you have written does not compromise your ability to file a patent. You may also wish to remove your post to protect patentability.