Figure 1: Seal Leak Test Fixtures @ 7,459,954 cycles
The need to specify and deploy a sealed arm created a parasitic loss of torque within the joint design. The seal loading needed to be carefully tuned to balance opposing goals – actuator torque loss and maximized seal life. Excessive frictional loading at the seal would result in an oversized actuator that would be incompatible with the application.
As the actuators and seal designs matured, the mechanical characteristics of the design were refined for weight and strength optimization. FEA models were created and evaluated to ensure physical strength was present only where it needed to be. The design was optimized for the casting process where uniform wall thicknesses are important to ensure consistent material flow without porosity during manufacturing.
Actuators – Servos
A custom actuator (motor drive / transmission) was needed to achieve the arm design performance goals. A global search and supplier selection was completed for an OEM Partner to develop and build the custom actuator. The actuator development effort began by first resolving the high-level project requirements and then building out the more detailed, component-specific requirements. Well defined component requirements led to an optimized design for mass, volume, and power.
The key aspects and characteristics of this full custom / purpose-built 6-DOF robotic arm are unique within the industrial / commercial marketplace:
- Sealed IP65 enclosure and electrical connections
- 10 Year life under harsh conditions with a 10 million cycle durability target
- Integrated Motion Controller and safety functions
- 48 VDC Operating Voltage
- Arm configuration flexibility that includes joint orientation and section length
- Mass optimized design with exceptional strength to weight ratio
- Supported custom end-effector design
- Application specific mount provided durable mount in space constrained environment
- End of arm motion accuracy ≤1°
The 6 DOF custom robotic arm leveraged a machinable design that is intended for casting at higher volumes. Custom seals and arm geometry prevent intrusion of environmental contamination. Custom actuators ensure that needed speed, acceleration, torque, and accuracy is achieved. Initial field trials for the first complete prototype arm have been completed, After ~6 months of daily use, the achieved performance and reliability have met and exceeded all program goals.