Precise
A number of forward-looking features ensure reliability and precision. The integrated fixed restrictor provides an effective safety buffer, protecting against overloading during high-speed gripper motions and preventing damage due to excessive forces. The integrated sensor slots in the medium and large sizes offer the advantage of cost-effective stroke sensing via sensors SMx. Their integration has resulted in a slim, compact design without any interference contours caused by external sensors. The new, compression spring-assisted gripping force retention provides more security in the event of a pressure failure. In addition, T-slot guides increase the torque resistance of the gripper jaws.

The double-acting piston drive gives the standard grippers stable kinematics and maximum repetition accuracy. A wide range of mounting options in the form of threaded, fitting and centering holes make the new generation of Festo standard grippers very flexible to mount.

Reliable
The parallel and three-point grippers DHxS have lightweight aluminium housing with integrated receiving hole for the pneumatic piston. The force generated by the linear motion is transferred to the low-backlash gripper jaws by means of lever kinematics. Since the lever is indirectly in mesh with the two gripper jaws via a piston rod, there is no need for additional synchronization.

The pneumatic pistons of the double-acting DHxS radial and angle grippers act on the gripper jaws, mounted on pivots in a gripper jaw guide, by means of a slotted guide system. As with parallel and three-point grippers, this means that there is no need for separate synchronization.

Festo Corp.

Pneumatic Tips

Enviably agile and purposeful, the mobile robot makes its way through grounds rendered off-limits to humans as the result of a chemical accident. Depressions, ruts and other obstacles are no match for this eight-legged high-tech journeyman. With a camera and measurement equipment on board, it will provide emergency responders with an image of the situation on the ground, along with any data about poisonous substances. Not an easy task—after all, it must be prevented from tipping over. But this risk seems a minor one as it confidently and reliably picks its way through the area. As a real spider would, it keeps four legs on the ground at all times while the other four turn and ready themselves for the next step.

Even in its appearance, this artificial articulate creature resembles an octopod. And no wonder—the natural specimen provided the model for researchers at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA. This high-tech assistant is still a prototype, but future plans envision its use as an exploratory tool in environments that are too hazardous for humans, or too difficult to get to. After natural catastrophes and industrial or reactor accidents, or in fire department sorties, it can help responders, for instance by broadcasting live images or tracking down hazards or leaking gas.

With its long extremities, the spider has a range of ways to get around. Some models can even jump. This is possible using hydraulically operated bellows drives that serve as joints and keep limbs mobile. With no muscles to stretch their legs, these creatures build up high levels of body pressure that they then use to pump fluid into their limbs. Shooting fluid into the legs extends them. “We took this mobility principle and applied it to our bionic, computer-controlled lightweight robot. Its eight legs and body are also fitted with elastic drive bellows that operate pneumatically to bend and extend its artificial limbs,” said Dipl.-Ing. Ralf Becker, a scientist at IPA.

The components required for locomotion, such as the control unit, valves and compressor pump, are located in the robot‘s body; the body can also carry various measuring devices and sensors, depending on the application at hand. Hinges interoperate with the bellows drives so that the legs can move forward and turn as needed. Diagonally opposed members move simultaneously, too. Bending the front pairs of legs pulls the robotic spider‘s body along, while stretching the rear extremities pushes it.

The special aspect of this high-tech helper: not only very light, it also combines rigid and elastic shapes in a single component; with just a few production steps, it can also be produced at low cost. To date, designs such as the mobile robot have been generated using conventional mechanical-engineering technologies—a time-consuming and costly undertaking. Researchers at IPA, on the other hand, rely on generative production technologies, and specifically on selective laser sintering (SLS) of plastics, a 3D printing process. In this process, step by step thin layers of a fine polyamide powder are applied one at a time and melted in place with the aid of a laser beam. This way, complex geometries, inner structures and lightweight components can be produced – with structures optimized much as if produced by Nature herself. The experts at IPA have a great deal of latitude in the design of their mobile robot; the leg modules, for instance, can be designed with infinitely variable load-bearing characteristics.

“We can use SLS to produce one or even several legs in a single operation; this minimizes assembly effort, saves materials and reduces the time it takes to build a robot. With the modular approach, individual parts can be quickly swapped as well. Our robot is so cheap to produce that it can be discarded after being used just once—like a disposable rubber glove,“ Becker said.

Fraunhofer-Gesellschaf

Pneumatic Tips

Compared with standard pneumatics, servo pneumatic solutions are up to 30% faster and use up to 30% less air. Servo pneumatic drives can also be freely positioned, making them up to 50% more economical than electrical solutions, as well as being more compact, light, and sturdy.

Savings from eliminating shock absorbers
With the DSMI-B, shock absorbers will no longer be needed on swivel modules, thus reducing purchasing, operational, and maintenance costs. At the same time, the DSMI-B offers flexible and compact solutions for a wide range of handling tasks in combination with the electrical terminal CPX and the CMPX or CMAX modules.

The sturdy semi-rotary vane drive with integrated measuring system can be used both as a soft-stop axis and for free positioning. The DSMI-B is designed for mass moments of inertia of up to 2050.3 lb-in.² (6,000 kgcm²). The DSMI-B demonstrates these strengths in a Festo laboratory ball-throwing demonstration. A ball held in the swivel arm of the DSMI-B is catapulted upwards in an even curve using a short stroke cylinder. As the ball travels through the air, the arm swivels 180° in just 0.5 seconds, brakes without vibrating, and catches the ball.

Soft stop function – CMPX
Rapid rotary and swivel movements at angles of up to 270° are simplicity itself for the compact module DSMI-B. The electronic end-position controller CMPX gently brakes the swivel drive in its end positions, even at very high speed. With this soft stop function, loads of up to 300 kg can be moved highly dynamically. The soft stop reduces cycle times by around 30% while diminishing noise, and permits virtually vibration-free movement to the mechanical end positions. The system can also be used to perform movements to two additional, user-definable intermediate positions without a fixed stop.

Freely positioned – CMAX
The possibilities of the DSMI-B are not limited to soft stop, however; free positioning is also possible. In order to achieve this, the swivel module DSMI-B is combined with the servo pneumatic positioning module CMAX. Like the end-position controller CMPX, the CMAX is one of the intelligent modules of the electrical terminal CPX and is designed for simple servo pneumatic control of pneumatic drives. Free positioning with servo pneumatics is particularly advantageous where the loads to be moved typically exceed 22 lb (10 kg). Using the CMAX, drives can be positioned precisely to within .008 inches (0.2 mm) and their force controlled accurately to 5%.

Integrates with Festo CPX
The end-position soft stop controller CMPX and freely positioned CMAX controller are easily integrated into the electrical terminal CPX, a versatile modular automation platform for valves and electrical control functions. In addition to positioning modules, other functions such as PLC control, electrical I/O, and pneumatics, in combination with the valve terminal MPA, can be integrated into the CPX for an all-in-one platform for machine OEMs.

Festo Corp.

Pneumatic Tips

Fabco-Air

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ContiTech Air Spring Systems is presenting a wide variety of products at the IFPE in Las Vegas, including its triple-convolution actuators, which are particularly well-suited for applications involving high lifts.

The company produces numerous versions of air actuators that are extremely robust, durable and more cost effective than hydraulic alternatives. The air actuators are often used in industrial manufacturing where harsh conditions usually prevail – dirt, dust and liquids can wreak havoc on the machines. In applications involving heavy caking and soiling of external surfaces – such as in the woodworking and textile machinery industries, conveyor systems as well as in offshore applications, in punch and forming presses, in sawmill machines and in the foodstuffs, construction or paper industries – air actuators function very well as ultra-strong, economical constructions. Since air actuators get by without mechanically operated parts like pistons, piston rods and friction seals, they are not subject to wear and require no maintenance. This gives them an edge over conventional cylinders. They are also more environmentally-friendly as they do not require oil.

The design of these dimensionally stable elements is comparable to that of an air spring. They are used to provide extreme force for lifting or exerting pressure where little space is available for installation. Whether for pneumatic lifting or pressing functions in the construction of machines, appliances or systems, ContiTech air actuators are outstanding performers across many different industries.

ContiTech AG

Pneumatic Tips

This actuator has precision end stop position, and zero backlash, it is available in 90º and 180º models with adjustable rotation, and repeatability of ± .02º of rotation.  It has a modular design which eliminates adaptor plates reducing machining and assembly time.  It can be mounted in any orientation, and has a temperature operating range of -35-80ºC.  The system requires 40-100psi and in a typical application will last up to 5 million cycles, and up to 10 million with maintenance.

Omega

Pneumatic Tips

Tolomatic

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The cylinder`s patented linear motor uses high-flux annular magnets on the actuator rod, surrounded by special windings on the stator coil. This effectively turns conventional linear motor design inside out. (In most linear motors, the fixed stator contains the permanent magnets and the moving element contains the coil windings.)

The new design is said to offer several significant advantages, including a low moving mass and the avoidance of flexible cabling to the moving parts. The cylinders have no external magnetic field and can be used in environments, such as machine tools, where swarf may be present.

Initially, the IP65-protected cylinders are available in two sizes – with 32mm and 40mm profiles and peak thrust force ratings of 35N and 52N – and in four stroke lengths from 15–45mm. Positioning repeatability is said to be ±0.5mm.

The cylinders can use the same mounting accessories as other similarly-sized Festo products, making it easy to mix and match different drive technologies. Although the cylinders use closed-loop control to ensure positioning accuracy, there are no servo parameters to set up – users simply teach the controller the two end-positions for the piston rod.

Festo has also produced a controller to partner the ADNE-LAS cylinders. The CMFL controller accepts feedback from the cylinder’s built-in magnetic encoders and maintains its drive output signal until the piston rod has reached the desired end-position. Unlike a solenoid actuator, the cylinders have a high power density and produce a constant force throughout their stroke – like a pneumatic actuator, though with lower force levels. Self-adaptive loop gain control decelerates the actuator movement as it nears the end of its stroke, providing automatic end-position cushioning.

The CMFL controls the movement of the piston rod in both directions and can store four different movement patterns, any of which can be selected and initiated via digital inputs. The controller also produces a “motion complete” output signal when the piston rod reaches its end-position.

The combination of controller and cylinder can handle stroke cycles (movements in and out) at up to 20Hz for up to 10 minutes without interruption. The system operates from a 48V DC SELV (safety extra-low voltage) source, and can also be run from 24V DC, with suitable de-rating.

www.festo.com

Pneumatic Tips

Aaron Dietrich, Tolomatic’s electric products manager, says that the patent-pending actuators (shown above) “provide an alternative to pneumatic cylinders with the added benefit of greater control of speed, acceleration and force”. They also offer an “affordable option for automating manual processes”.

The round-bodied electric actuators are available in sizes equivalent to 5/8, 1 and 1.5-inch bore non-repairable pneumatic cylinders. They accept Nema 11, 17 or 23 frame stepper and servomotors, and the acme leadscrews are available in three lead sizes per model to optimise speed or force.

The actuators, which come with metric-threaded rod-ends, can accommodate six different sensing or switching technologies including reed, solid-state PNP or NPN, normally open, flying leads or quick-disconnect. The switches are activated by a magnet inside the thrust tube.

www.tolomatic.com

Pneumatic Tips

Roller screw actuators have several advantages over hydraulic or pneumatic actuators for many applications, especially those involving heavy loads and fast cycles. For example, the controls are simpler, eliminating the complex system of valves, pumps, filters and sensors that make up hydraulic and pneumatic systems. Other benefits include a small system footprint, long functional life and low maintenance requirements. And because roller screw systems don’t require high-pressure fluid, they reduce noise levels and are not subject to potentially hazardous fluid leaks.

inverted roller screw mechanism Rollers screws come in two basic kinds of configurations; the inverted roller screw mechanism, top, and the standard configuration roller screw, bottom.

Roller Screw Technology
Roller screws convert rotary torque into linear motion, similar to acme screws or ball screws. But roller screws can turn considerably faster and cycle more frequently than both acme and ball screws, making them an ideal fit for demanding, continuous-duty applications. Similarly sized roller screws are more efficient than acme screws and can carry larger loads than ball screws, handling loads up to 779,000 lbf.

The difference in performance is due to the design for transmitting forces. The number of contact points in a ball screw is limited by the ball size. In roller screw systems, multiple threaded rollers are assembled in a planetary arrangement around a threaded shaft, which converts a motor’s rotary motion into linear movement of a shaft or nut. The rollers feature radiused flanks that deliver point contact, similar to balls on a raceway, with only the radius near the point of contact included as part of the profile. This design allows a larger radius with additional contact points to fit into the existing space, lowering the stresses within the system and lengthening its functional life. Because the number of contact points is greater, roller screws have high load-carrying capacities, as well as improved stiffness. This typically means that a roller screw actuator takes up less space in order to meet a designer’s load requirement than a similarly sized ball screw.

Roller screws are designed to have larger radii at the point of contact, meaning that more contact points will fit within the same relative space. This lowers stresses and lengthens functional life compared to a comparably sized ball screw system, top.

High load capacities mean that roller screws have some major advantages in service life. For instance, in a 2,000 lbf average load application applied to a 1.2 in. screw diameter with a 0.2 in. lead, a roller screw will have an expected service life that is 15 times greater than a ball screw. Typical ball screw speeds are limited to 2,000 rpm and less due to the interaction of the balls colliding with each other as the race rotates. In contrast, the rollers in a roller screw are fixed in a planetary arrangement by a journal and gears at the ends, so they do not have the same speed limitations. Hence, roller screws can work at 5,000 rpm and higher, producing comparably higher linear travel rates.

Versatile nut options let you balance between backlash and load capacity demands and cost trade-offs. Some common nut configurations are the single nut, split nut and double nut designs. The most common configuration, the single nut, has a long service life and low backlash under 0.001 in. In split nut designs, the nut is split transversely and a precision-ground spacer sits between the front and back halves. The split nut configuration effectively eliminates backlash and also reduces the dynamic load rating by about 38%. As the name implies, the double nut arrangement uses two nuts preloaded against each other on a single screw. This design offers similar life expectancy as a single-nut design as well as decreased backlash, but typically costs more than a single-nut configuration.

Roller Screw Size Specification
Roller screw variables include the diameter, lead and sealing. When preparing the component specification, be sure to take into consideration the budget, maximum linear speed, maximum load, maximum stroke, necessary precision level, tolerance to backlash, the contaminants present and the needed level of protection.

A few key calculations help determine the ideal parameters for an application. For example, roller screw nut speeds cannot exceed their mechanical speed limit, which is dependant on the screw diameter and the lubrication method. Systems lubricated with oil should not exceed 140,000/d_o, while grease-lubricated roller screws systems shouldn’t surpass 90,000/d_o.

In high-speed roller screw applications, the roller screw shaft typically sets up natural frequency vibrations, which should be taken into account by calculating the critical speed. This speed is determined by the screw diameter, length, loading direction and bearing arrangement. The rotational speed of a roller screw should be kept below the critical speed, defined as:

n_crit = 86.4 x 10⁶d_of_s / l²

where:

n_crit = critical rotational speed under zero axial load (rpm)
d_o = screw diameter, in. (mm)
fs = support bearing factor
l = screw’s length, in. (mm)

Another phenomenon to avoid is buckling. Buckling occurs when the compressive load on a screw’s shaft is too great for its diameter. The buckling force is determined by the screw length, diameter and type of bearing supporting the screw. The compressive load should be less than the buckling force, defined as: F_b = 81.3f_bd_o⁴ / l²

where:

f_b = buckling force, kN
F_b = buckling force bearing factor

Another factor to consider is the motor size. A motor is selected by calculating the required torque as a function of load on the system and lead of the roller screw and comparing it to available motors and power transmission components. For applications that require a specific motor, roller screws with a lower or faster lead, belt or gear reductions can be configured into the system.

Protection and Maintenance
While correctly specified and maintained rollers screw systems can still fail from metal fatigue or abrasion of the thread flanks, other failures can typically be prevented. For optimal performance and life, roller screws, like other lead screws, should be well lubricated and must tolerate contaminants including abrasives, metal chips and non-lubricating fluids.

Although the friction created by the rolling screw design is minimal compared to sliding friction, it can still cause heat build-up, which can eventually lead to a costly failure. Lubricants should be used to dissipate heat in order to avoid wear and premature failure. In general, roller-screw life can be increased by regular grease and oil replenishment. Maintenance intervals depend on the screw size and operating conditions. Typically KP (DIN 51825) consistency two bearing grease should be applied. Some applications with higher duty cycles may need a high-performance gear oil with EP additives. Lubrication rates vary according to the screw diameter, number of rollers and the amount of heat to be dissipated.

Providing sufficient protection against contaminants is also critical to long functional life. For instance, if metal chips get into the nut assembly, the roller screws may grind them into a lapping compound, which will cause spalling and eventual catastrophic failure. Shaft wipers, bellows, shrouding and enclosures protect roller screw components from environmental contaminants, and should be selected according to specific application requirements. For example, wipers can be added to the front or back of the nut to scrape particulates from the threads throughout the screw stroke. Additionally, force tubes that house roller screws keep lubricants in, while preventing contaminant infestation. Force tubes with IP67 ratings are available in a wide array of mounting options.

Improper loading is another possible cause of roller screw failure. As a general rule, lead screws do not tolerate applied moments or side loading, so high-precision slide rails should be used to carry these loads and make certain that loading on the nut is co-axial to the lead screw.

Although roller screws may have a higher initial cost than alter-native motion actuation systems, they usually provide significant cost savings in the long run. In fact, a properly specified and maintained roller screw system typically costs half that of the cumulative cost of ball screw systems, since they do not need to be replaced or maintained as frequently.

www.exlar.com

Pneumatic Tips