5.1 Initial Proposal

Introduction

For this project, we were tasked with identifying and solving a problem best solved with a robot or system of mechanisms. As a group, we did a deep dive into past projects and ideas we were interested in pursuing. After group deliberation and conversation with TAs, we decided to go with the Card Dealer idea. Our Card Dealer mechanism will rotate and dispense cards with accuracy to 6 different players. The motivation behind this choice was our shared interest and excitement of board games. A common issue that comes up during this time is who will deal the cards out. Furthermore, not everyone can hand cards out with ease. With the creation of our mechanism, one won’t have to debate or have talent to hand out cards, but instead can hand it over to a robot. Not only will this solve a problem that we each universally face, but it also will be interesting to see just if we can create a mechanism that not only deals cards but flicks them as well.

Proposed Mechanism

The proposed mechanism focuses on mimicking a human wrist with a flicking motion. To accomplish this we intend to use a 4-bar linkage and adjust the link length to obtain a unique velocity profile that follows our intended flicking motion. The design of the mechanism will have to take into consideration how we want to mount the card/item and the specifics of the flick we intend to pursue.

Additionally, complex motion profiles could be achieved with the inclusion of two four-bar mechanisms to better suit our design. Other alternatives we have reviewed such as the scotch and yoke, quick return, and cylindrical cam mechanisms could provide us with a similar velocity profile to the desired flicking motion.

Later on, we will also look into using a Geneva mechanism to introduce rotational motion into our project while also allowing us to set desired points where we want the cards/items to be dealt.

Scope of Work

For this project, we have four goals: we want the machine to rotate and stop at 4 different spots, dispense cards at least 6 inches from the machine, and flick one card at a time. We aim to complete all three goals and if time allows, further increase the distance the cards are dispensed. We would need to perform the Grashof condition, mobility, position, kinetic, and velocity analysis. Other additional steps we would need to consider is calculating gear ratios for the rotation of the machine and timing of the forces with the necessary velocities. We do not have affiliations to extend the work.

Preliminary Design Ideas

The design of our Card Throwing Mechanism is heavily motivated by the anatomy of an actual human arm and wrist. The primary intention of our mechanism is to successfully be able to deal a card across a table. Thus, by linking three sets of four-bar mechanisms, we aim to enact a sweeping and flicking motion to project the card forward (Figure 1.0). 

Figure 1.0: Card Throwing Mechanism Design

Figure 2.0: Kinematic Diagram

In Figure 2.0, we can see that the mechanism has four grounded links overall, and is mainly driven by w1. The motion of w1 directly drives w2, which is meant to mimic the “arm” of a human as it moves forward to throw the card. The motion of w3 and w4 mimic the flicking motion of the wrist and hand as the arm comes to a stopping motion at the end of the thow. The angular motions w2, w3 , and w4 do not complete full rotations, and return to the start of their curve. Alternatively, w1 is the only angular rotation that makes a complete revolution.

Figure 3.0: Sections of Four-Bar Mechanisms

In order to properly analyze the motion of our mechanism, we split it into three sections of 4 bar mechanisms (Figure 3.0). For each of these sections we analyze the mechanisms using Grashoff and Gruebler methods. 

We found that Section 1, denoted in red, operates under Grashoff Class I motion, meaning that there is one bar that completes a full rotation, operating similarly to a slider crank (Figure 3.1). By using Gruebler’s Equation, we see that this section has one degree of freedom, which is confirmed by our kinematic diagram in Figure 2.0.

In Section 2, denoted in purple, Grashoff analysis illustrates that this section operates under Grashoff Class II motion (Figure 3.2). In other words, there are no links that complete full rotations. After analyzing this section using Gruebler’s Equation, it is evident that the mechanism operates under one degree of freedom. This is again corroborated by the kinematic diagram in Figure 2.0.

Section 3, denoted in orange, operates under Grashoff Class I motion (Figure 3.3). By using Gruebler’s Equation, we find that the mechanism operates under one degree of freedom. This is corroborated by the kinematic diagram in Figure 2.0.

Furthermore, we can also analyze the mechanism as a whole, as seen in Figure 4.0. In agreement with previous calculations, we found that Gruebler shows one degree of freedom for the mechanism.

Figure 3.1: Section 1 Design Analysis

Figure 3.2: Section 2 Design Analysis

Figure 3.3: Section 3 Design Analysis

Figure 3.4: Mechanism Design Analysis