I designed and built this mechanism as part of a group for a Design of Planar Machinery class at UC Berkeley. Our goal was to automate the process of cutting fruits and vegetables in the kitchen. The device rectifies AC wall power into 12VDC to power a motor, which actuates a blade attached to a slider crank mechanism. The entire system is encased in a protective acrylic shield to obstruct access to the blade. Once cut the vegetables fall neatly into a container, and can be easily removed for cooking or consumption.
An early sketch of the mechanism with a manual feed and conveyor belt
The entire mechanism is mounted to an ultra high molecular weight polyethylene (UHMWPE) base for stability, portability, and cleanliness. Additionally, the slider mechanism is mounted to a machined aluminum platform that is connected to the base using machined spacers. The collection chamber sits flush with this platform for catching vegetables.
As part of our safety considerations, an acrylic case was cut using a laser printer and assembled to fit around the device. Additionally, an emergency stop and power switch were installed to quickly cut power to the operating mechanism if needed.
The powertrain for our mechanism consists of a 12V DC motor with a built-in gearbox. The two sprockets are connected with a ANSI No. 25 Chain.
The axle mounts, cranks, and connecting rods interface with one another through precision pins, bearings, and shaft collars. These allow for smooth rotation of the parts during operation.
The slicing assembly consists of off-the-shelf guide rails and nylon sliders, as well as a modified hardened steel blade. Aluminum mounting blocks are used to interface between the driving links and the blade, while securing the blade to the slider.
A kinetics analysis was performed to determine the torque needed apply 10 pounds of force. This force value was found experimentally by slicing a cucumber on a scale and measuring the difference between the cucumber’s weight and the peak weight recorded when pressing a knife into the vegetable. Our calculations suggested a peak torque value of 5 in-lb, so to be safe (and have the ability to cut harder vegetables) we sized our motor to 20 in-lb.
Three parts were analyzed for stiffness using the SolidWorks FEA package: the crank (short link), the connecting rod (long link), and the pin that connects them. These were chosen because they are the smallest components that take the most load. However, since the links are aluminum and the pin is stainless steel, the deflection was quite small. For the full analysis please refer to the long-form report here.
Have more questions? Take a look at the long-form report for this project: