Mechanical engineers often need a basic, space-saving linear guide when designing technology that performs simple tasks, such as vending machines. Since such technology does not handle high loads, high speeds or high positioning accuracy, intricate linear guides are not necessary. However, most solutions on the market are very advanced, leaving manufacturers forced to either pay for features they do not need or develop their own linear guide.
Solution from igus: Toothed belt drive axis starting at $150
igus is now offering the drylin ZLW eco, a ready-to-install entry-level series that is making simple positioning and adjustment tasks extremely efficient and, above all, cost-effective. “A toothed belt axis of this entry-level series with a stroke length of 100 millimeters starts as low as 150 dollars,” said Stefan Niermann, head of igus’ drylin linear and drive technology division. “In comparison, a toothed belt axis from the standard series, which has high-performance features and is therefore unnecessary to use for simple operations, costs almost three times more.” The carriage and shaft end supports are produced by injection molding, which is more cost-effective than mechanical filling used for metal component production. “This also reduces the number of components and thus the installation efforts for every eco linear axis, which in the end is reflected in the low prices of this entry-level series,” explained Niermann. A further cost-saving element of the drylin ZLW eco is the plain bearings used in the sliding carriage, which are made of iglide high-performance plastics. “iglide bearings are forty percent more cost-effective than conventional rolling bearings and 100 percent maintenance-free in operation,” Niermann said. Without compromising the smooth-running operation and durability of the standard series, users can simply install the eco axes and save time and money with the maintenance-free, dry-running triboplastic bearings.
Entry-level series in two sizes
The entry-level drylin ZLW eco has two installation sizes: 0630 and 1040. The base is an anodized drylin W profile made of clear anodized aluminum. At the ends of the profile are plastic shaft end supports for drive technology. A neoprene toothed belt is tensioned between the shaft end supports, which pushes and pulls a solid plastic carriage with a positioning accuracy of 0.3 millimeters. The stroke lengths can be individually adjusted by the user. Due to its lightweight construction, the toothed belt axes weigh only 0.3 kg and 0.7 kg, and can move loads up to 3 kg or 10 kg respectively. Matching motor kits also are available.
Aventics’ new universal electric actuator for industrial applications features a highly flexible design for customization to the customer’s application.
The new Aventics best in class universal electric actuator is heavy-duty and suitable for normal or extreme environments. The highly flexible design allows the actuator to be customizable to the customer’s application. A wide range of best in class features include: highest output torque and accuracy, operating temperature, integrated gear box, and unlimited radial and linear positional control. The actuator can be used in many factory automation applications and in food, beverage, processing and packaging, etc.
The universal electric actuator features a flexible customer interface for integrated or remote applications and allows for both active or passive actuation. Communications protocol include CAN, PWM, analog, etc. The actuator has buffered battery voltage monitoring with under voltage lockout, and is 12V or 24V ready. On board diagnostics and feedback are provided, and it is field programmable/addressable. The actuator features various mounting configurations including NEMA 23 or 34 attachment/compliance, and meets IP50, IP67 and IP69. Motor technology can be BLDC or PMDC.
Universal electric actuator specifications:
See additional information online at: Aventics Universal Electric Actuator.
With the second generation EMC electromechanical cylinder, Rexroth expands the possibilities for utilizing these compact drive units. With their hygienic design and IP65 protection class, they are now suitable for applications with frequent cleaning cycles in the food industry. The new size EMC100-XC-2 increases the power density for feeding forces of up to 56 kN, e.g., for applications in forming technology. An optional force sensor allows decentralized process controls without a higher-level control system.
The axis penetrates the narrow working area and approaches different positions, or varies the pressing force: electromechanical cylinders combine the advantages of a slim cylinder with the possibilities provided by digital control of electrical drives. The ready-to-install drive units consist of anodized aluminum profiles in ISO standard dimensions, with an integrated ball screw drive. They cover variable-length strokes of up to 1,500 mm. In the newly developed second generation, Rexroth has implemented the principle of hygienic design in the cylinder body. There are no recesses or slots in which dirt can be trapped. The screws on the end face can be optionally sealed. Together with the version in IP65, which is also valid for the timing belt side drive, the EMC withstands frequent cleaning cycles and spray water.
For use in applications with particularly aggressive cleaning agents, the version in IP65 + R ensures a long service life with seals and scrapers made from chemically stable materials. A pressure compensation port prevents the occurrence of overpressure or negative pressure in the cylinder for the versions in IP65.
Additional size and optional force sensors
As the seventh size, the EMC100-XC-2 variant completes the product range. XC stands for extra capacity. The EMC-100-XC is longer than the EMC-100- NN-2, a larger axial bearing and larger ball screw drive provide up to 56 kN of feeding force—at the same profile cross section. This widens the usage for electromechanical cylinders from Rexroth towards more powerful applications in forming and machining.
Furthermore, Rexroth offers all sizes with an optional force measuring pin. This can be placed on the end of the piston rod as well as on the timing belt side drive. The sensors transmit the values with a +/- 10V analog signal to the drive. A Motion Logic System, which can be optionally integrated in the Rexroth drives, evaluates these signals and enables decentralized process control without a higher-level control system. The certified Safety on Board functions that are integrated in the drive simplify implementation of the Machinery Directive with low engineering effort.
In addition, the new housing is equal in its dimensions to those of the first generation. Interchangeability is thereby ensured. The technical data of the second generation is the same or better for all sizes, in comparison with the previous series. As a function of the piston rod position, the new EMC catalog now contains diagrams for the permitted radial piston rod force. With the newly designed lubrication points, users can integrate the electromechanical cylinder in central lubrication concepts. On request, the modules can be delivered by Rexroth without initial lubricant allowing users to apply industry-specific lubricants.
Rexroth provides a wide range of servomotors and drive controls which are suitable for the different sizes. Users can also operate the electromechanical cylinders using motors and controllers from other manufacturers. An online configurator supports selection of the suitable motor attachment kit.
Piezo elements are used in a variety of configurations to provide rotary or linear motion in applications that require short strokes and fast response times. Piezo elements that are used to produce motion through the inverse piezoelectric effect are known as piezo actuators. These devices provide very small displacements with extremely high resolution. When one or more piezo elements are combined, the assembly is commonly referred to as a piezo motor. Piezo motors require more sophisticated drive electronics, but can provide longer travel lengths than piezo actuators.
Depending on the arrangement of the piezo elements and the type of movement they generate, piezo actuators can generally be grouped into four main types: longitudinal, shear, tube, and contracting. Despite their different configurations and uses, these piezo actuators all operate on the same basic principle: movement is directly proportional to the voltage applied. Because they operate solely on the solid-state dynamics of the piezoelectric material, with no mechanical parts, piezo actuators do not experience wear.
A piezo actuator can be integrated with frictionless flexures and levers to form a flexure guided piezo actuator. The flexures and levers multiply and translate the motion of the piezo stack to provide travel up to a few mm, in one or multiple axes. Because the motion of the flexures is based on elastic deformation of the material, there is no friction and no wear.
Unlike piezo actuators, piezo motors typically incorporate mechanical elements to produce motion, which makes them susceptible to wear. Take ultrasonic piezo motors for example. They operate by electrically exciting a piezo actuator to produce high-frequency oscillations. The actuator is preloaded against a runner via a coupling element. Although the motion (oscillation) of the actuator does not create wear, the interface between the coupling and the runner presents a source of friction, and therefore, wear.
Piezo inertia motors – also referred to as “stick-slip” motors – also use a piezo actuator and runner to produce motion. But in this case, the actuator expands slowly and contracts rapidly. Through a coupling element, the runner is able to move along with the actuator during expansion, but during the rapid contraction, the runner slips on the coupling and effectively stays in place. For rotary motion, a variation on this design uses “jaws” that engage with a very fine thread screw and turns the screw as the actuator expands. In either design, the reliance on friction and the “stick-slip” effect makes wear inherent in piezo inertia motors.
A piezo motor design with little or no wear is the piezo stepper motor. Piezo steppers consist of multiple piezo actuators and operate by coordinating clamping and shear motions between the actuators and a runner. Unlike other piezo motor designs, because each of the actuators (also referred to as “legs” due to their walking-type motion) in a piezo stepper motor make contact and then lift off of the runner, friction is minimized and wear is virtually eliminated.
The new Spindasyn SEZ electric cylinder from AMK Automation is a ready-to-install linear drive motor system in which the rotor is pressed directly onto the screw. Featuring high and constant force, high precision and position accuracy and high energy efficiency, the closed-loop positioning and force control of the SEZ make it an ideal alternative to other linear technologies such as pneumatic or hydraulic cylinders, rack and belt drives and linear motors. With several options available for screw and strength length, motor type and acceleration, the SEZ provides high rigidity without additional wearing parts.
With the ability to set multiple travel profiles, the SEZ can be easily integrated into machine automation processes and applications such as tubular bag packaging; blister packaging; carton forming; palletizing; pick and place; cross-cutting; labeling; wrapping; strapping; filming; insertion; order picking; sealing plastics; printing; paper processing; textiles; food and beverage; machine tooling and more.
Like servo motors, stepper motors are available in both rotary and linear designs. When an application requires force (rather than torque) output and can operate in open loop control, a linear stepper motor is often the preferred solution. Although linear stepper motors are available in both variable reluctance and hybrid designs, the more common version is hybrid linear stepper motors.
In a hybrid linear stepper motor, the base, or platen, is a passive steel or stainless steel plate with slots milled into it. The forcer contains motor windings, permanent magnets, and laminations with slotted teeth that serve to concentrate the flux that’s created when current is applied to the coils. The teeth of the forcer and the platen are staggered by ¼ tooth pitch in relation to one another to ensure that constant attraction is maintained and that the next set of teeth will come into alignment as current is switched in the coils. This means that for each full step of the motor, the forcer moves along the platen by ¼ tooth pitch.
Whereas variable reluctance linear stepper motors can only operate in full step mode, hybrid versions can operate in either full step or microstepping modes. Microstepping, which divides the step angle into smaller increments, enables higher resolution motion and better control of speed and force. Because each phase of the motor is driven with (theoretically) ideal sine waves, 90 degrees apart, microstepping also allows the current to increase in one winding as it decreases in the other, providing smoother operation at low speeds than can be achieved with full- or half-step operation.
For guiding the load on hybrid linear stepper motors, either mechanical roller bearings or air bearings are typically used. (Because the platen in a hybrid linear stepper motor is passive, it can serve as the air bearing surface.) The magnetic flux between the forcer and platen creates a strong magnetic attraction, so these support bearings actually serve two purposes – to guide and support the load and to maintain the correct air gap between the forcer and the platen.
Like other linear motor designs, hybrid linear stepper motors can incorporate multiple forcers onto one platen, with each forcer moving independently. In addition to smooth low-speed operation (obtained with microstepping control), they are also able to achieve very high speeds and accelerations with high resolution and low to moderate force generation.
With simple mechanical construction and easy setup (no servo tuning required), hybrid linear stepper motors are ideal for applications that can operate in open-loop mode and that require either high speed with low force production or very smooth motion at low speed.
Featured image credit: H2W Technologies, Inc.
Resonance occurs when the resonant frequency (also referred to as the natural frequency) of an object or system is equal or very close to the frequency at which it is being excited. This causes the object or system to vibrate strongly and can result in unexpected – and sometimes catastrophic – behavior.
When one oscillating object or system (a piezo drive or controller) drives another system (a piezo motor or actuator) at or near the natural frequency of the second system, the second system will oscillate at a high amplitude at a specific frequency. When damping effects are small, the resonant frequency of the system is approximately equal to its natural frequency.
f0 = resonant frequency (without load) (Hz)
kT = piezo stiffness (N/m)
meff = effective mass (kg)
The resonant frequency of a piezo motor or actuator depends on its material composition, shape, and volume. For example, a thicker piezo element will have a lower resonant frequency than a thinner element of the same shape. In addition, attaching a load to a piezo motor or actuator reduces its resonant frequency – the higher the load, the more the resonant frequency is reduced. In manufacturer specifications, the resonant frequency given for a piezo actuator assumes that it is unloaded and one end is fixed or attached to a mass that is significantly larger than the actuator.
f0‘ = resonant frequency with added mass (Hz)
m´eff = meff + additional mass (kg)
In an electrical circuit representing the piezo element, the frequency at which the impedance of the circuit is at a minimum is the series resonant frequency, fs. Conversely, the parallel resonant frequency, fp, in the equivalent circuit occurs when impedance in the circuit is theoretically infinite (assuming mechanical losses are ignored). This is also known as the anti-resonant frequency, fa.
The series and parallel frequencies are suitable approximations of the minimum and maximum impedance frequencies – fm and fn, respectively – and therefore are used to determine the parameters of the piezoelectric motor or system. Maximum response of a piezo system occurs between fm and fn. Piezo systems with a higher resonant frequency will have a better phase and amplitude response, which means that the operating frequency can be higher.
Theoretically, the resonant frequency is the operating frequency at which the piezo material vibrates most readily and converts electrical energy into mechanical energy most efficiently. However, piezo systems (especially actuators used for positioning) are often operated below their resonant frequencies in order to minimize the phase shift between the driving signal and the actuator.
When operated below their resonant frequencies, piezo actuators act like capacitors, with displacement being proportional to the stored charge. With a rapid increase in control voltage, a piezo system can typically reach its nominal displacement in 1/3 the period of its resonant frequency. However, this causes large overshoot, which must be compensated for by the controller.
tmin = minimum rise time (s)
f0 = resonant frequency (Hz)
Feature image credit: Stack Exchange Inc.
Servo2Go.com has just added remarkable new additions to its broad range of cost-effective 24V electric linear actuators from Dyadic Systems. The SCN6 series actuators are compact yet powerful integrated mechatronic cylinders that feature a motor, encoder, drive and actuator in one integral package.
Dyadic Systems has developed the linear actuator drive mechanism such that the screw and nut are optimized for high accuracy, long life and low cost while delivering high speed and peak thrust. This blend of low-cost and high performance could only have been realized by the advanced technology of Dyadic Systems. These new product concepts give engineers a wider range of options to eliminate over-design.
SCN6 series Mechatronics Cylinders are available in stroke lengths to 300mm and 500N (51kgf) maximum thrust and are constructed using an extruded aluminum body with 303 stainless for the shaft and rod tip. Actuators can easily be operated via 24VDC signals from PLCs or relays, and can be connected in networks of up to 16 axes. Servo Actuators from Dyadic feature:
• Teach pendant, PLC pendant or PC Tool Kit programmable
• +-0.1mm repeatability
• 0.3mm backlash
• 50-300mm stroke versions
• Up to 200mm/sec max. speed
• 16 discrete position program capacity
• IP40 sealed, with optional IP54 sealing
• Electric actuators—programmable in 15 minutes
• The SCN6 starts from only $465 each
• Moves can be relative, absolute, force controlled, and more
• All actuators run on 24VDC – easy to connect to your existing power supply
• Air cylinder replacement mode and move sequencing available in the cylinder
Electrical and controls engineers are normally tasked with selecting and integrating the electronic components that go into a motion control system, such as motors, drives, controls, feedback devices, and HMIs. In doing so, their primary concerns tend to be on making the various components communicate with each other, working through complex equations for drive tuning, and programming HMIs to ensure the user can operate and troubleshoot the system with relative ease.
And while some of these tasks require a fundamental knowledge of mechanical principles – particularly torque, speed, and inertia – rarely do they go into the nuances of how linear guides and drives (ball screws, belts, rack and pinions) work and their impact on the electrical side of the system. But even if you never have to size or select them, it’s helpful to understand the basic principles and equations for linear motion components that are common in motion control systems.
L10 bearing life – Bearing life (or L10 life) is a fundamental concept for sizing any recirculating bearing. This article explains what L10 life is and how to calculate it.
How to calculate move profiles – The type of move profile an application uses determines the maximum speed and acceleration, which affects motor sizing and drive tuning. This tutorial describes the two most common move profiles and how to calculate velocity and acceleration for each.
How to calculate acceleration – More information (and equations) specifically dealing with acceleration.
How to calculate drive torque for ball screws – Continuous and intermittent torque values are key to motor sizing. This article explains how to calculate torque during constant speed, torque during acceleration, and torque during deceleration.
Torque considerations for keyed shafts – This article demonstrates the disparity between the torque that can be transmitted by a solid shaft versus a keyed shaft, including equations for calculating when shear failure and crushing failure will occur.
Ball screw back driving – Screws are often used in vertical applications because they prevent the load from catastrophically crashing if the motor loses power. But if the load is too heavy, it can still cause the screw to back drive. This application note provides equations for calculating back driving torque.
Ball screw buckling – When a screw is used in a vertical application, it’s important that the load doesn’t exceed the column strength of the screw, which depends on the screw length and the end bearings used. This tutorial explains why buckling occurs and how to calculate the buckling load for a given screw.
If you’re new to linear guides and drives, you may also want to check out the linear guide and ball screw glossaries. They include descriptions of each technology, including technical specifications and details on construction.