In small mobile robots, decreasing the number of actuators is usually desirable to reduce the size and weight of the robot, but it is usually at the expense of the robot’s degree of freedom (DOF). This work presents the development and preliminary experimental testing of a novel Legged Piezoelectric Miniature Robot (LPMR) driven only by a single piezoelectric unimorph actuator and yet fully capable of being maneuvered to move forward, turn right, or turn left. The underactuated motion is achieved by exploiting the bending vibration modes disparity of the piezoelectric actuator at different driving frequencies and designing specific positions of the robot’s legs to generate a differential-drive-like mechanism. The speed of the robot can be controlled through regulating the magnitude of the applied voltage. The proposed underactuated system is experimentally verified and a preliminary characterization of the LPMR in terms of its forward and turning speed versus applied voltage and payload is investigated and reported

1. 1
Steerable Miniature Legged Robot
Driven by a Single Piezoelectric
Bending Unimorph Actuator
Audelia G. Dharmawan, Hassan H. Hariri, Shaohui Foong, Gim Song Soh,
and Kristin L. Wood
IEEE International Conference on Robotics and Automation
Singapore
May 29 - June 3, 2017

2. 2
Motivation
-10
0
10
20
30
40
50
60
30 50 70 90 110 130 150
TopSpeed(bodylength/s)
Body Length (mm)
PZT LIPCA Motor
*Bubble Size:
Robot Mass
Our robot
6 actuators
Qu et al.
6 actuators
Baisch et al.
12 actuators
Rios et al.
Can we develop a maneuverable piezoelectric miniature robot using only a
single actuator?
Bidirectional motion using 1 PZT actuator
Hariri et al., ICRA 2016
• Mobile robot miniaturization
1 actuator = 1 DOF
Over-actuated
Basic Robot Architecture
PZT Unimorph ActuatorLegs
Plot of some existing miniature legged robots

3. 3
Locomotion Principle
• Exploit bending modes of the piezoelectric
actuator and leg placement along the robot’s
moving direction to achieve bidirectional motion
• Further exploit the leg placement on the opposite
sides of the mid-sagittal plane to create a
differential-drive-like system for steering motion
Leg Trajectory
Antinode
Top view
Mid-sagittal plane
Mid-sagittal plane
Left Turn
Right Turn
Side view
ActuatorLegs
Motion Direction
Left side of antinode Right side of antinode

4. 4
Robot Design
𝜑 𝑛 𝑥 = sin(𝛽 𝑛 𝑥) + sinh(𝛽 𝑛 𝑥)
−
sin 𝛽 𝑛 𝑙 − sinh 𝛽 𝑛 𝑙
cos 𝛽 𝑛 𝑙 − cosh 𝛽 𝑛 𝑙
(cos 𝛽 𝑛 𝑥 + cosh(𝛽 𝑛 𝑥))
∅ 𝑛 𝑥 =
𝜑 𝑛(𝑥)
(𝜌𝐴) 𝑒𝑞 0
𝑙
𝜑 𝑛(𝑥)2 𝑑𝑥
• Mode Shapes𝑓1 𝑓2 𝑓3
Modeshape
Length of beam (cm)

5. 5
Experiment
𝑓𝑛 =
𝛽 𝑛 𝑙
2𝜋𝐿2
(𝐸𝐼) 𝑒𝑞
𝑏(𝜌 𝑝 𝑡 𝑝 + 𝜌 𝑚 𝑡 𝑚)
• Resonance Frequencies

6. 6
Steering Trial