Many industrial robots and robot systems rely on electric motors for their motion. There are situations though where hydraulic orbital motors are the better choice. After providing an introduction to this form of rotary motion, this blog explains when and why to consider switching to hydraulic actuation.

Principles of Hydraulic Orbital Motors

Liquids are incompressible, which makes them an effective means of transmitting force. A pump uses rotary motion to move fluid, and a hydraulic motor reverses the process, turning fluid flow back into rotary motion.

Like pumps, there are many forms of hydraulic motors, all with different characteristics. The hydraulic orbital motor is a type particularly suited to low speed applications that need high torque. At its heart there’s a gear wheel that rolls around the inner surface of another gear.

The inner gear, or rotor, is connected to an output shaft, which turns as the rotor orbits the inside of the static, or stator, gear. This assembly is a gerotor, and it’s powered by fluid acting on one side of the rotor to apply torque and make it turn.

Hydraulic orbital motors deliver a lot of torque from a compact package. They can rotate in both directions and be held in place, and they are more forgiving of shock loads and impacts than electric motors. In addition, they avoid the need for a gearbox, as is required to slow down the rotation of an electric motor. These characteristics make them useful in robotics applications.

Hydraulic Orbital Motors in Robotics

The four types of robotic application are:

• Joints and arms
• Manipulators
• End-of-Arm-Tooling (EoAT)
• Conveyors

In small robots with light payload capabilities, electric motors are the better choice for joints. They are compact, easily controlled, and not prone to overheating. However, as payloads increase and torque demands go up, hydraulic orbital motors become more attractive. They can provide hundreds of pounds of torque, will not overheat, and can hold the arm in position when needed.

A point to note about hydraulic orbital motors is that they need a pump, a hydraulic accumulator, and control valves. These can be placed in the base or pedestal to avoid adding mass to the arm. Furthermore, when the accumulator is sized appropriately, multiple motors can share these base components.

Many robot systems need additional motion axes within the cell. For example, palletizing and shrink wrapping systems need heavy duty rotary tables, and large welding systems often need a positioner that turns the weldment for optimal torch orientation. When the payloads on these units are in the hundreds of pounds, hydraulic orbital motors offer space, energy and cost savings over large motors with gearboxes.

The other component every robot needs is end-of-arm tooling. For grasping and placing product this is usually a gripper of some description, often using pneumatic grippers or suction cups. In some applications though, the robot holds a tool and takes it to the workpiece. Robotic deburring is an example. Depending on the rotational speed and torque needed, a hydraulic orbital motor may be a better choice than an electric motor. Their superior tolerance for impacts and shock loads typically improves durability over electric motors.

Hydraulic orbital motors are also used to drive conveyors. Again, in light duty applications, electric motors offer a better combination of cost and performance. Where the belts will be heavily loaded though, and especially if they are subjected to shock loading, superior torque and speed characteristics, combined with impact resistance, give hydraulics an advantage.

Choosing Hydraulic Over Electric Rotary Motion

Hydraulic orbital motors provide high levels of torque at low speed from a compact package. In addition, they are reversible, can be held in position without needing a brake, and withstand shock impacts. Together, these make them a durable, cost-effective source of motion in high payload robotic applications.

Impro Fluidtek offers an extensive range of hydraulic orbital motors for use in robotics and other applications. Contact us for details.