**Author details**

its maximum output force capability. It is a crucial parameter for dynamic robots because it allows the actuator to be used in sensitive activities such as human contact, equipment operation, and non-structured environment exploration. In addition, the actuator with great dynamic range can do hard work activities such carrying, push or pull weights. In summary, high dynamic range is an important characteristic for a four-legged dynamic robot application.

The minimum resolvable output force is evaluated by the resolution of the spring deflection sensor. Resolution gives the minimum spring deflection that can be detected. This deflection

Both the SEAs have the same spring stiffness in this comparison. Also, both actuators have the same spring deflection sensor which is a linear encoder. Therefore the minimum output force

The HSEA dynamic range is 1500:1 while the ESEA range is 150:1. It shows that the hydraulic

This chapter presented a comparison between the two series elastic actuator (electric SEA and hydraulic SEA) for four-legged dynamic application. The actuators were digitally prototyped and the comparison was made considering actuator's bandwidth, output impedance, time

Although the ESEA has a better time response, both actuators have its responses within desired range for a dynamic robot application. The bandwidth also is not a problem for both actuators because all systems examined have large bandwidth compared with the given application. HSEA and ESEA presented good output impedance with a slightly better behavior from hydraulic SEA. Both actuators have two peaks on the output impedance, one peak due to

Power density and dynamic range are the two key parameters that differs the weight carrying dynamic robot application from others dynamic robots applications. In these two parameters, the HSEA showed a better performance than ESEA. The HSEA's power density is 100 times higher than the ESEA's. Moreover, the dynamic range of hydraulic SEA is 10 times higher than the electric SEA dynamic range. The results showed the HSEA as the better series elastic actuator for this task and it could contribute for the research of SEA applied on robot links.

Further work is required on the simulation of SEA, specially the HSEA, on a dynamic robot. With this simulation, the advantages and drawbacks of the implementation can be analyzed and quantified. Also, a construction of a real aluminum alloy based prototype and testing its performance in a real time environment for evaluating the actuator's performance under force, position, velocity and mixed controllers. Another future work is on the development of tuning strategies between the spring stiffness – actuator bandwidth and elastic energy store relation‐

controller gains and another due to the resonance frequency of the system.

times the spring stiffness gives the actuator minimum resolvable force.

is the same for both which is 3N.

230 Recent Advances in Robotic Systems

**5. Conclusions**

ship.

SEA has a range 10 times bigger than electric one.

response, power density, and dynamic range.

Arnaldo Gomes Leal Junior1 , Rafhael Milanezi de Andrade1,2\* and Antônio Bento Filho1

\*Address all correspondence to: rafhael.andrade@ufes.br

1 Department of Mechanical Engineering, Universidade Federal do Espirito Santo, Vitória, ES, Brazil

2 Department of Mechanical Engineering, Bioengineering Laboratory, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
