Machine builders face a vexing problem when there’s a need to rotate large or unwieldy products in assembly, handling, and packaging applications. Engineers often must select and size an electric motor; evaluate direct, belt, or gear drives; find bearings that can handle the loads and give long life; and assemble the entire package and fit it into often-limited space.
A better option may be a guided pneumatic swivel module that provides a versatile, rotating drive for large and hard-to-handle loads.
All-in-one swivel drive
The new DSM-HD swivel module from Festo Corp., Hauppauge, N.Y., combines a high performance semi-rotary vane drive with a precision heavy-duty bearing, letting it accurately turn loads through adjustable angles up to 270° – without the need for additional bearings or guides.
Capable of generating significant torque from a standard (1.5 to 10 bar) compressed-air supply, the DSM-HD handles high axial and radial forces as well as large moments of inertia. This reportedly makes it suited for demanding applications involving heavy or offset loads. The unit is especially beneficial in fully or semi-automatic manufacturing handling and assembly operations where forces change as the module rotates. One such case is where forces increase after the module swivels a work-piece holder into position on an insertion machine.
The modules come in six different versions spanning 12 to 63 frame sizes. The units produce maximum torque of 40 N-m (at 6 bar) and accommodate maximum axial forces of 1300 N and radial forces up to 1800 N.
Because the DSM-HD has a higher load capacity than alternative products, engineers often can specify a smaller module with significant space and cost savings. And all the modules have a compact construction to facilitate integration inside a machine. For example, the 25 frame-size model measures 83 × 83 × 99 mm.
A caged precision ball-bearing race on the swivel’s periphery is preloaded to maximize rigidity and eliminate backlash. The bearings are designed specifically to maintain running accuracy when subjected to high thrust and cantilevered forces; radial and axial eccentricity are both held to less than 0.02 mm on the 12, 16, and 25 frame size modules, and to less than 0.04 mm on the larger modules, under maximum load conditions.
The drive’s rotary-vane chamber seal maximizes power output and efficiency by minimizing air leakage. The design also ensures that the actuator produces smooth and uniform motion throughout its range of movement, even when operating near the upper or lower pressure limit. A dual-vane version of the drive is available for applications that demand higher torque.
Unlike swivel modules that only offer fixed angular displacement, users can adjust DSM-HD modules up to a maximum swivel angle of 270°, depending on the model and type of end-position cushioning. Setting the start and stop angles is straightforward: the two end-position cushioning mounts are simply clamped at the desired positions in a circular slot on the rear face of the module, and then finely adjusted using an Allen key.
Users can choose between hydraulic shock absorbers for maximum energy absorption or adjustable elastomer cushioning for fast cycle times — both types provide end-position accuracy of better than 0.1°. DSM-HD swivel modules are also available without end stops when applications require external cushioning. The vane drive’s stop lever incorporates a magnet, letting users incorporate end-position sensing by simply fitting Festo SMx proximity switches in alignment slots on the cushioning mounts.
When selecting a swivel module and deciding how to mount it, machine designers must evaluate a number of application-specific factors. These include the axial and radial forces acting on the module, the torque required to start the load moving, the mass moment of inertia (which is particularly critical for the stops and cushioning of rotating masses), and the required end-position accuracy.
Software simplifies calculations
Because it can be difficult to visualize or estimate mass moment of inertia and time consuming to calculate it manually, Festo has developed a software program to help designers quickly and easily tackle this task.
The program works with disks, blocks, flanges, grippers, and other shapes and calculates total load and total mass moments of inertia. Users can choose from several methods to input data. For example, the “Block” option lets users specify the length, width, height, and density of an object and the distance from the center of gravity to the axis of rotation. Another option is for shafts that are inline or at right angles to the axis of rotation.
The free inertia-calculation software can be downloaded from the engineering tools support portal on Festo’s website.
According to company officials, the DSM-HD also simplifies installation, compared to other swivel modules on the market. The vane drive has a hollow shaft, letting electrical cables and air tubes be routed through the body of the drive for controlling attachments such as clamps and grippers. Both the flange and module body incorporate threaded mounting holes and use centering rings for quick and accurate alignment. For extra versatility, the body has mounting holes on three sides, as well as on its front and rear faces, so the module can be fitted securely in most any desired orientation.
The swivels provide a versatile tool in designers’ arsenals when developing multi-axis handling units, according to the company. And standardized interfaces facilitate mating to electric and pneumatic linear slides, and to an extensive range of mechanical and vacuum end effectors.
For more information, visit www.festo.com/us.
