#Product Trends
“Donut” actuator takes on rotary applications
Toroidal Ram Systems Ltd., based in Auckland, New Zealand, has developed a unique toroidal-shaped rotary actuator for use in high torque, heavy duty applications.
The Torlite is said to be the world’s first curved-ram hydraulic actuator capable of angular rotations of up to 120°.
How it works
The Torlite operates similar in principle to simple and robust single-acting hydraulic cylinders. Rather than being linear, however, the design features a curved cylinder body which houses a single-piece, curved hydraulic rod. The Torlite’s two single-acting, toroidal shaped cylinders oppose each other to produce rotary motion in both directions.
According to company officials, the new rotary actuator has succeeded where other toroidal-shaped actuators have failed, thanks to its floating seal and gland assembly. “The floating seal gland that the rod moves through really only serves the purpose of holding the seals and allowing a constant seal to the rod as it flexes,” said design engineer James Kells. “As the rod end is rigidly fixed (not a pivot point), the gland isn’t primarily responsible for withstanding side loading, as is the case with a straight cylinder. We use standard, off-the-shelf pressure and wiper seals in the gland. The pressure seal is of narrow width to reduce seal wear of a curved rod passing through it. We’ve never had any issues with premature seal wear.”
The innovative design allows for smooth operation and complete sealing throughout the actuator’s range of movement. Currently the Torlite actuator is capable of producing 100° output rotation, with an increase to 120° in the works.
Simple manufacturing
How the curved rods are cost effectively made is usually the first question on the minds of potential users, said Kells. “We manufacture the curved rods and mounting foot as a one-piece item on a 5-axis machine. The rods are then polished, induction hardened (by a custom-made induction coil) and then chromed.”
An induction-hardened chrome finish ensures a sufficient hardness depth and corrosion protection to withstand abuse typical of the earthmoving industry, he continued. Nitriding the rods would be fine for applications where the rods aren’t prone to impact loads. Dimensional tolerances on the finished rods are within 0.07 mm (less than 0.003 in.).
“There is nothing fancy about the manufacturing process on a 5-axis machine, so costs are nothing out of the norm,” said Kells. Because the toroidal ram features only two primary moving parts — the toroidal rods extending and retracting within the cylinder housing — the unit is much simpler than helical actuators, which have dozens of complex parts and seals.
And there are no worries about long lead times or delivery delays. “As the majority of the Torlite actuators parts can be manufactured by any 5-axis CNC outfit, we see this as a big advantage in meeting unit supply to potential companies interested in implementing the technology,” he said.
Fewer moving parts also tend to mean less chance of wear and breakdown. Servicing of the unit primarily involves replacing seals after a certain number of operating hours. That is typically performed on the machine without special tools, resulting in minimal downtime. Helical actuators, in contrast, must be removed from the equipment for servicing by a trained technician.
Engineering specs
Driving and holding forces of the Torlite actuator are directly related to both operating hydraulic pressure and the size of the hydraulic cylinder. The flow rate of hydraulic oil determines operating speed.
Currently, three different sizes have been developed for tilting hitches on 6, 14 and 20-ton excavators. However, any size actuator can be readily designed, provided the cylinder body and rod can be produced on a 5-axis CNC machine.
Typical maximum operating pressure is 3,500 psi. Higher pressures and greater torques are possible, only limited by stress levels at the foot of the curved rod. The 14-ton unit, for example, produces approximately 12 kNm (8,850 lb-ft) of torque at 3,500psi. The Torlite holding torque is identical to its drive torque, whereas helical actuators benefit from an internal geometry that gives higher holding torque.
Hydraulic flow requirements on a tilting hitch can generally be adjusted to provide application flexibility. Orifices in a custom valve block (which also includes check and relief valves) can be changed to vary the flow and, thus, speed of the actuator.
The compact, narrow-bodied design is appropriate for use in confined spaces. Radial dimensions are similar to those of a comparable helical actuator, but axial length of the Torlite is about one-third less, and it is about 10% lighter. And the device is expandable: multiple cylinders can be axially offset to work together and generate higher torque outputs.
Potential applications
The Torlite is built for heavy-duty tasks that require a robust design and high torque outputs. The product can be engineered into a specific application or supplied as a standalone actuator where upper and lower mounting plates serve as attachment points. In addition to use in construction-machines, it is suited for marine, defense and agricultural equipment, solar array and satellite dish tracking, industrial automation and aerospace applications.
And while the current hydraulic unit focuses on high-torque applications, it can be adapted to lighter-duty pneumatic systems. Toroidal Ram Systems is looking to partner with other manufacturers interested in adapting the technology into various engineering industries and applications.
