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When it comes to linear actuators, selecting the right drive technology can be a precise balancing act as there is no ‘one size fits all’ solution.
Due to the breadth of applications – from automated packaging lines and pick-and-place operations to complex machines such as 3D printers – making the correct choice is less about concentrating on a single aspect than finding the optimum balance of performance from a variety of different factors.
Most electromechanical linear actuators rely on one of five common drive train types: ball screws, lead screws, timing belts, rack and pinion tracks and linear motors.
Ball screws are ideal for high duty cycle applications and where high force density, precision and repeatability are required. The rolling ball bearings reduce friction and deliver high mechanical efficiency, even in continuous use. Ball screws can achieve moderate speed.
Lead screws are suitable for low duty cycle applications, or those requiring small adjustments. They typically only offer about half the efficiency of ball screws, so require twice the torque to achieve the same thrust output. However, lead screws provide cost-efficient and compact solutions for high-force applications.
Timing belts are simple, robust mechanisms for high-speed applications requiring long life and minimal maintenance, where precision greater than 100 microns is sufficient. They are efficient and easy to operate and can run at 100 percent duty cycle. Timing belts are available in longer lengths than screw drives.
Rack and pinion systems are useful for very long travels requiring high speed but are not known for their precision. They offer high force density but require regular system lubrication. In addition, removing system backlash from this type of drive train is not always possible, and they can be quite noisy in operation.
Linear motors offer high speed, acceleration and precision. Cost is the principal drawback, while force density is also less than other drive systems. The absence of a mechanical connection between the moving and static components of linear motors makes their use difficult in vertical applications.
The selection options for a linear drive can be grouped into the following categories: precision, expected life, throughput and special considerations (PETS).
For precision, always start with an understanding of needs relative to resolution. The other considerations are repeatability and velocity control. Linear motors and ball screws are typically best in terms of precision characteristics.
With lifespan, mechanical efficiency is the primary consideration, unless the requirement is for a dirty or harsh operating environment. High drive train efficiency is synonymous with long life and reduced energy consumption. Factors such as wear resistance, dirt resistance and maintenance requirements are also important. Due to their high efficiency and limited maintenance needs, timing belts are the go-to option in this category.
Throughput can be considered by first scrutinising the speed and acceleration or deceleration characteristics of each technology – depending on the length of linear travel required. If the need is for longer travel where more of the cycle time is spent at top velocity, speed is the most important. If shorter moves are required, acceleration and deceleration characteristics will take precedence. Linear motors are unparalleled when it comes to throughput.
Some other considerations to take into account when looking at each technology include material and implementation costs, while force density is a further increasingly important factor to bear in mind as machine designs continue to miniaturise, particularly when specifying end effectors or tooling mounted to an axis.
For more information about the four key performance characteristics to consider when choosing a linear drive train from our white paper click here to download.
Article contributed by Olaf Zeiss, product manager, Actuators Electromechanical & Drives Division Europe.
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In a world of constant technological advances, the photonics industry is seeing rapid growth with no signs of a slow-down. Photonics is the branch of technology concerned with the properties and transmission of photons. Photons are applications involving a laser. Lasers often conjure up images of an evil scientist plotting to destroy an unsuspecting city with a “laser death ray.” To the contrary, laser applications are commonly used in many markets to improve the quality of life – think healthcare or autonomous cars.
Applications in the photonics industry usually require a precise motion control system to function properly. In addition to these sub-micron specifications, many applications require high speeds and long lengths of travel. To meet these requirements, a linear motor stage is usually the best option. Parker offers a range of linear motor stages to satisfy these application needs. From miniature linear stages such as the miniature square rail, mSR, to completely custom designs, we can provide the linear stage that provides speed and precision.
Parker’s product and expertise in this area were on display at SPIE/Photonics West Exhibition, the world’s largest photonics technologies event in January in San Francisco. Parker displayed XY custom systems made of linear motor stages to simulate performance in laser based applications including laser scribing/cutting and cellular scanning. Customer feedback reiterated the need and desire for these products out in the field. Products need to be fast and accurate while maintaining their Abbe errors (stiffness, smoothness and flatness). Parker has designed products specifically to provide Abbe specs above the industry standard along with the drives and controllers to complete the motion system, Learn more about Parker’s linear motor stages.
Other types of electromechanics also apply. Many applications still use a screw-driven stage on the Z-axis. Designers will choose this route since they usually do not require the precision or speed provided by a linear motor stage for this axis. The other advantage is that a magnetic counterbalance is not needed when the unit is not in use. Parker’s MX80S and MX45 series are ideal for these applications as they provide the needed precision at a reasonable price.
22 Feb 2018
Linear actuators are typically grouped into two principal types: fluid power actuators that operate on differential pressure, and electromechanical actuators driven by an electric motor. Increasingly, electromechanical solutions are providing an attractive alternative to hydraulics in a wide and diverse array of automation systems.
Electromechanical systems offer:
In complex applications, electromechanical solutions can be particularly advantageous as they provide control over the entire motion profile. Moreover, integral encoders accurately control speed and position, while some solutions can also control and monitor torque. Programmability means that motion and force profiles can be changed using software without having to shut down and reconfigure the machine.
In terms of energy consumption, unlike hydraulics, electromechanical solutions use power only when they are performing work, thus contributing to significant savings. Also, due to their minimal impact on the environment, solutions of this type are strongly preferred in applications where clean operation is important or desired.
An example case for electromechanical solutions is put by Industrie Cometto SpA, an Italy-based designer/manufacturer of trailers, semi-trailers and self-propelled vehicles, which wanted to replace hydraulic systems on its EMT (Electric Modular Transporter) to achieve greater flexibility in terms of speed and control, and make it suitable for use in ATEX classified atmospheres.
The traction and steering systems on the EMT are now equipped with Parker electromechanical products. Each transporter can have from four to 16 wheels, all of which have to follow a perfect trajectory to ensure coordinated motion. With this in mind, the drive system has to guarantee precision in terms of speed, position and torque control. An AC, three-phase, 2.3kW electric motor is fitted to the traction system on the EMT.
With regard to the steering system, the position of each wheel axle is controlled electronically using an encoder. Here, each suspension unit is linked to the load platform by a rotation system driven by a 1kw electric motor. The motor is controlled by an absolute encoder and managed by Cometto’s central processing unit.
Parker supplies the complete motor and drive packages for both of Cometto’s non-ATEX and ATEX EMT vehicles. For the latter, Parker provides its EX (explosion-proof) servo-motors with AC890 variable speed drives.
The EX series is a range of permanent magnet explosion-proof brushless servo motors characterised by excellent motion quality, dynamic acceleration/deceleration capabilities and high torque output over a wide speed range. Parker’s AC890 is a compact, modular system variable speed AC drive engineered to control speed and position of open-loop and closed-loop, single- or multi-motor AC induction or PMAC motor applications. The AC890 variable speed drive is compatible with any AC motor and many speed/position feedback options.
Ultimately, electromechanical solutions offer engineers a number of potential benefits over hydraulics that are proving difficult to ignore when it comes to new system designs. These can include one or many of quality, reliability, maintenance, performance, cost, ease-of-use, noise levels and operational response.
EX-Series Explosion Proof (ATEX) Brushless Servo Motors
AC Variable Frequency Drives, kW Rated - AC890 Series
Article contributed by Edi Gherbezza, electromechanical, motion & drives
application manager & business development manager for Motion Systems Italy
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Checking the IP rating of an actuator initially can help rule out any that will not be suitable for the environment. It may also save you money. For example, the Parker 400XR Series has an IP30 rating. While it will not have any protection against moisture, it does have intrusion protection against fingers. The XE Series, an economical alternative to the XR Series, does not have an IP protection (i.e. 00). If there are concerns about injuring fingers, XR should be selected. However, if the intrusion protection is not necessary and the XE specs work for the application, the customer can save money by with the XE. Now if a customer needs protection against moisture as well, the XR Series is not the right choice. Instead, they should use the HMR Series, which has an IP54 rating.
Parker offers a wide array of linear positioners suitable for applications in a variety of environments, even the harsh ones. Our IP rating differs from product to product and application to application, so we are confident the right fit can be found. Once determined, sealing and shielding guidelines are followed for all our linear mechanics to meet the required customer specifications. In addition to seals and shields, positive pressure ports can be included on linear stages as well. This allows customers to purge unwanted contaminants inside their unit, keeping the performance and life cycle at a maximum.
What if you are not certain which sealing and shielding technology is needed for their application? Parker will work directly with you to provide custom engineered solutions. We will discuss your requirements and can determine the best product to use based on the environment. Forming this partnership throughout the process ensures you receive the best solution for your application - which is Parker’s ultimate goal.
To learn more about Parker’s linear stages our sealing and shielding capabilities, visit our website, or contact us to discuss your application needs.
Article contributed by Patrick Lehr, product manager for precision mechanics, Electromechanical and Drives Division North America, Parker Hannifin Corporation.
25 Jan 2018
With its high power density and flexible mounting capabilities, permanent magnet direct drive servo motors like the Parker PM-DD series have a proven track record in many manufacturing applications. Let's take a look at five successes spanning various industries.
As the world's communications infrastructure continues to grow and evolve, the demand for fiber optic cable has been increasing. With Parker distributor Cross Automation in Charlotte NC, we were able to provide PM-DD motors for a vertical lathe, used to dispense glass for fiber optic wiring. The combination of smooth low-speed operation, compactness, and the ability to mount directly to the rotating shaft made the PM-DD a winner over standard servo motors.
Machine tools demand accuracy, and in the second case study, the task at hand was to repeatedly index a table that was three feet in diameter. With displacement occurring 1.5 feet (457 mm) away from the motor centerline, its high resolution (20 bit) absolute encoder was critical to the application. Thanks to the PM-DD's high load carry bearings, (1500 N in this case) where previously a conventional servo motor and worm gear solution was used, the PM-DD proved to do the job while eliminating the worm gear. The drive train was simplified and ongoing maintenance associated with the mechanical gearing was eliminated. This solution was sold by Faber Associates, Parker distributor based in Clifton NJ.
Automotive assembly is a rigorous application with hundreds of interdependent operations, all of which must function reliably, at the risk of costly downtime. A rotary table was used in the operation of adjusting vehicle headlights. Simplicity and high positioning resolution were the main factors leading to the adoption of the PM-DD in an application solved by Parker distributor Reco-Wesco from Indianapolis. Being able to mount the motor directly to the table eliminated the need for multiple mechanical components that would have required maintenance and been a potential failure mode.
Automotive industry testing applications often duplicate real-life scenarios that the finished vehicles will be exposed to, but must take into account the worst-case situations. In this case, the PM-DD motor was used for an electronics test bench. Part of a multi-axis assembly, the test bench would simulate the rough vehicle road conditions, including a rollover, that the electronics might be subjected to. PM-DD was preferred over a standard servo motor due to its smooth, slow speed, operation, good bearing support and high torque. This solution was sold by Parker distributor RSA of Fond du Lac WI.
The fifth and final application was in the life sciences field. A PM-DD motor was used for an indexing table that carried five stations to support the assembly of medical devices. The first station was to load the part, second applied adhesive, third was for UV curing of the adhesive, fourth was inspection and fifth was where the part was unloaded. In this case, the PM-DD replaced a pneumatic indexing table. Key to its success was a smooth start and stop operation versus the previous pneumatic solution. Also, the PM-DD with Parker P-Series Drive allowed for a variety of indexing locations to be programmed providing more flexibility than a more traditional rotary indexing table. This solution was provided by Automation Incorporated, a Parker distributor out of Minneapolis MN.
Learn more about the PM-DD by visiting our Precision Direct Drive Rotary Servo Motor Series Product webpage to buy or download a Parker P series
Direct Drive Rotary Motors catalog.
Article contributed by Jeff Nazzaro, gearhead and motor product manager, Electromechanical & Drives Division, Parker Hannifin Corporation.
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