This document describes research on developing expressive movements for a guitar-playing robot arm. It discusses constraints of 7 degrees of freedom and maintaining the end point in a steady plane. It presents methods using inverse kinematics and adding sine waves to joints to create different expressions like delight, joy, and sad through varying joint movements, functions, positions, frequencies, and phases. The goal is to make the robot movements more human-like and able to convey emotion. Future work involves integrating more delicate strumming and picking mechanisms.

1. X Arm: Guitar Robot
Ning Yang, Amit Rogel, Roger
Robinson
Jiahe Qian

2. Towards a more expressive robot
What makes a robot more human-like:
1. Have as many moving joints as possible
2. Small details / movement
3. Make sense / convey certain emotion
Constraint:
1. 7 degrees of freedom
2. Maintain end point in a steady plane

3. Method
Inverse Kinematics and Geometry:
● maintain the original end-joint position and facing angle

4. Method
Addition of Sine Waves:

5. Result
We tried:
● Different combination of joints used
● Different functions on how each joint moves
● Different initial starting position
● Different scale / frequency of movement

6. Expression 1: Delightful
j1_x = 0.25*sin(2*pi*Fc*t);
j2_x = 0.2*sin(4*pi*Fc*t);
j4_x = -asin(j1_x*d1/d2)-j1_x; %Geometry compensation for j1
j6_x_a = asin(j4_x*d2/d3); %Geometry compensation adjust for j4
j6_x_b = j1_x + j2_x +j4_x; %Angle compensation for j1, j2, j4
j6_x = scale* ( j6_x_a*(1-deep) +j6_x_b *deep) ; %Combine j6_x_a, j6_x_b

7. Expression2 : Joy
j1_x = 0.25*sin(2*pi*Fc*t);
j1_x = clip(j1_x,max,min); % Clip sine to create rest
j1_x = smooths(j1_x,’g’, stdev); % Gaussian smooth the sharp points
j3_x = -j1_x; % Movement cancel with j1_x
j4_x = 0.25*sin(2*pi*Fc*t);
j5_x = 0.15*sin(2*pi*Fc*t); % Little detail of shaking head
j6_x = 0.25*sin(2*pi*Fc*t + 0.25*pi) ; % Phase create follow through movement

8. Expression 3: Sad
j1_x = 0.05*sin(2*pi*Fc*t);
j2_x = 0.2*sin(2*pi*Fc*t*1.2);
j3_x = (1/5) * (sin(2*pi*Fc*t*0.8)+sin(7/3*2*pi*Fc*t*0.8)+sin(7*pi*Fc*t*0.8)); % Complex movement create hesitation
j5_x = -j3_x; % Cancel movement with j3_x
j6_x = 0.4*sin(2*pi*Fc*t*1.2+0.25*pi*1.2); % Phase create follow through

9. FUTURE
Future Project Work:
• Integration with more delicate strumming / picking
mechanism