6.1 Project Proposal for Mortar and Pestle
Introduction
The inspiration of this project came from a daily chore that Landon’s family has. Landon’s little brother takes several crushed supplements daily. The grinding materials must be made of ceramic or wood to prevent leaching from materials such as steel. Current solutions include manually grinding with a mortar and pestle or using a manual ceramic burr grinder. The process is time-consuming. The available automated solutions are not conducive to small to medium-scale grinding due to the cost and size of such machines. In order to solve this problem, we want to design a motorized mortar and pestle machine.
Description of Problem
There are two main categories of motion for mortar and pestles: pounding and grinding. Pounding involves reciprocating the pestle up and down in the mortar with significant force to break the shell of the objects being pounded. With grinding, downward pressure is applied in a circular motion around the mortar. We want to focus on the grinding aspect of this problem.
For more information on the motion of pestles, see the videos below.
Short video: How to use a mortar and pestle
Long Video: How to use Mortar and Pestle
The main design challenge for an automated mortar and pestle that grinds is creating a mechanism that can work all of the surfaces of the mortar using planar mechanisms. An ideal motion for this would have a joint that allows the pestle to operate circularly around the mortar, creating a constant force profile around the mortar. However, this three dimensional motion is complex and does not have a trivial solution. Alternatively, we can create a planar pestle mechanism with a rotating mortar in order to access all surfaces of the mortar. In this case, we may need to couple the rotating aspect of the mortar with the planar pestle mechanism to a single motor. In the event of coupling these motions, we will need to consider how we will allow the system to operate at various speeds and if independent speed control is needed for each motion.
Description of a Proposed Mechanism That Could Solve this Problem
The mechanism will be a three or four bar mechanism. It will be either a slider crank or a crank rocker, depending on which of the three preliminary designs is chosen. The mechanism will convert the rotary motion of a motor to oscillatory or reciprocating motion of the pestle as well as rotational motion of the mortar in the case of the first two proposed solutions. The third solution would convert the rotary motion of the motor into a combination of rotary and linear motion of the circular pestle, with the mortar remaining stationary. Any of these three options would offer an effective way to quickly grind pills into a fine powder without excessive manual labor.
Proposed Scope of Work for Final Project
The scope for this project is to design and build a motor-driven mortar and pestle (M&P). The ultimate goal for this automatic M&P is to crush medical pills for patients without access to the manual ceramic burr grinders and other industrial machines. However, since the final product will be a prototype, in order to determine success, the final deliverable will be subject to crush a softer item, around the hardness of a smartie. Overall, the goal is to make the M&P from wood or ceramic. This will allow for easy manufacturing of specific designs and will improve aesthetics.
Prior to fabrication, we will perform position, velocity, and acceleration analysis to predict the path and motion of the mechanism before manufacturing. This will ensure the reciprocating/oscillating motion will cover the motion needed to crush our product. SolidWorks modeling and assembly will also be essential in ensuring the mechanism can be assembled and move without any interference. We will also perform force analysis on our mechanism to ensure we have enough output force in our pestle to crush our target product, as well as to ensure that our links can withstand these forces. This will allow us to determine possible alternate material and dimensions of the links we need to ensure they will not fail.
The overall interest/affiliation to extend the final product will be for Landon's brother, Levi, who needs to take crushed pill medication every day, as well as anyone else who doesn't have access to equipment to crush their pills.
Preliminary Design Ideas
For this project, the group will decide between one of the three ideas presented below. The first of these ideas mimics a traditional mortar and pestle, which involves a rotating mortar and a vertically reciprocating pestle. The second idea is similar to the first, but the pestle has rotational motion and oscillating motion (similar to a ball and socket joint). The final idea is much different than the first two, as it mimics a Chinese tea grinder with a rotating and linearly reciprocating grinding wheel.
Grashof Conditions:
Design #1:
S = L2 = 2in; L = L1 = 5 in; P = L3 = 4 in, Q = L4 = 4 in
S + L = 7 in < 8 in = P + Q
Continuous motion is achieved.
Design #2:
S = L2 = 3in; L = L1 = 5 in; P = L3 = 5 in, Q = L4 = 4 in
S + L = 8 in < 9 in = P + Q
Continuous motion is achieved.