Danielle Collins - Motion Control Tips

Improved tails allow better cleanings on sanitary conveyor platform

December 12, 2018 By Danielle Collins Leave a Comment

Perhaps the most important feature of a sanitary belt conveyor is the ability for it to be thoroughly cleaned. Dorner’s new AquaGard 7350 V2 Series with tip-up tails checks off that box…and then some.

The AquaGard 7350 V2 with tip-up tails provides ample access to the inside of the conveyor for effective, fast cleanings and easy maintenance. Tails can be tipped up in just a few seconds with no tools, and then retracted and locked back into place with the same minimal effort.

Tip-up tails are standard on the AquaGard 7350 V2 straight-belt models and are also available on straight-running modular belt units. They come with improved strength in the tail for more rigidity and no flexing, as well as supporting the belt/chain closer to the tail for improved performance.

Debuting at PACK EXPO 2018, the AquaGard 7350 V2 is built for numerous sanitary applications in baking, snack food, pharmaceutical, pet food, packaging, and other industries that require wipe-down and occasional washdown cleanings of the conveyor. The new conveyor comes in straight belt, as well as modular belt straight and curve models. Belted LPZ, modular belt LPZ, and positive drive models will be available in the coming months.

The AquaGard 7350 V2 is the safest, most advanced modular curve chain conveyor in the industry today. The modular belt curve conveyor has no openings greater than the international standard of 4 mm, even within the curves, which increases safety by eliminating pinch points for operators. Added safety measures are also achieved by covering the upper and lower chain edges and fully containing the drive system, which reduces catenary belt sag and conveyor noise.

Space reduction is another improvement on the AquaGard 7350 V2. The modular belt conveyor system is designed to maximize available plant space by keeping the footprint as compact as possible. Infeed and outfeed sections are a compact 18 in., further saving valuable floor space.

Dorner

The truth about VFDs and power factor

December 7, 2018 By Danielle Collins Leave a Comment

Power factor is essentially a measure of how effectively a piece of equipment (or an entire facility) uses electricity to produce useful work, such as heating, lighting, or motion. Electricity companies monitor power factor and often charge customers a penalty if their power factor falls below a specified threshold — typically 0.90 or higher.

Fortunately, most electrical loads in residential buildings are resistive (heating and lighting, for example) and have a high power factor, so consumers aren’t normally subjected to this metric. Industrial plants, on the other hand, typically have high inductive loads that significantly reduce their power factor. For example, AC induction motors — which are used for driving pumps, fans, compressors, and conveyors — have relatively low power factors, even when their capacity is put to full use. And when these motors are lightly loaded, their power factor drops even lower — sometimes approaching zero.

When an induction motor is heavily loaded (top), the voltage and current waveforms are nearly in-phase (small displacement), and power factor is high. When the motor is lightly loaded (bottom), the wave forms are out of phase (large displacement) and power factor is low.
Image credit: Yaskawa America

There are several methods of improving power factor in an industrial facility, but when the main culprits are induction motors — especially induction motors not operating at full load — applying variable frequency drives (VFDs) is often the best solution.

Recall that in an AC induction motor, power is supplied directly to the stator and a magnetic field is induced in the rotor. The power supplied to the stator is referred to as “real,” or “active” power because it produces torque. The power used to induce the magnetic field in the rotor is referred to as “reactive” power because it does not actively produce work. The combination of real power and reactive power is referred to as “apparent” power. Real, reactive, and apparent power are often depicted on a power triangle.

In an ideal system, power factor (PF_D) is the cosine of θ, which equals real power (P) divided by apparent power (S).

Note the subscript, D, in the power factor notation. In the power triangle, θ represents the displacement (phase difference) between voltage and current. Thus, this expression of power factor is often referred to specifically as the displacement power factor, PF_D.

For resistive loads, all (or nearly all) of the power used is real power that produces useful work — heat or light, for example. Therefore, current and voltage remain in phase (θ = 0), and the power factor is near unity (i.e., 1). But the reactive power required for inductive loads — to induce a magnetic field in a rotor, for example — tends to pull the current out of phase with the voltage (hence, a larger θ angle), causing a lower power factor.

The amount of real power required by an induction motor varies with the load, but the amount of reactive power (power required to generate the rotor’s magnetic field) is constant regardless of the load. Thus, when an induction motor is lightly loaded, the ratio of real power to apparent power decreases, resulting in a lower power factor.

Using VFDs to drive induction motors can improve power factor — but it’s not the panacea that some manufacturers suggest.

Variable frequency drives typically have very high PF_D values. This is because the DC bus capacitors supply the necessary reactive current to the motor for inducing the rotor’s magnetic field, and the AC supply line only has to supply real power. This means voltage and current remain almost perfectly in phase, with very little displacement, and the power factor can be at or near unity.

But VFDs also introduce harmonic current distortion. And because harmonic currents don’t produce useful work, they are reactive, thus negating some of the power factor benefits of the VFD.

To determine the true power factor, PF_T, which includes the effect of harmonic distortions, we use the equation:

THD = total harmonic current distortion

Fortunately, there are ways to reduce this VFD-induced harmonic distortion and minimize its effects on power factor. For VFDs that use a standard, diode-based rectifier, adding impedance via a line reactor or DC link choke will reduce THD.

Another option is to use an active front end (AFE) drive, which is a VFD that uses IGBTs, rather than diodes, to rectify the incoming AC power to DC. Active front end drives have significantly lower THD than standard diode-based rectifier designs. For example, and AFE drive typically has THD around 5 percent, where a standard VFD with a diode-based rectifier can have THD in the range of 45 percent.

Q: Why does the utility care how efficiently a plant or equipment uses the power it supplies?

A: Because low power factor causes higher line currents, which put more stress (primarily in the form of heat) on cables, transformers, and other equipment. Also, the lower the power factor, the more apparent power (kVA) the utility must supply to meet the real power (kW) requirements.

When do you need a linear amplifier versus a PWM drive?

November 29, 2018 By Danielle Collins Leave a Comment

Servo drives — also referred to as servo amplifiers — can be classified by the type of output stage they use: pulse-width-modulated (PWM) or linear. Of the two types, PWM drives are more common in general motion control applications because they provide more power to the motor, have higher efficiency, and are generally smaller and lower cost. However, while they are sufficient for most industrial applications, PWM drives create both audible noise and EMI (electromagnetic interference). They also produce minute vibrations that can interfere with sub-micron level positioning.

For applications that require extremely smooth motion, no audible noise, and little or no EMI, linear servo drives — commonly referred to as linear amplifiers — are preferred over PWM drives.

EMI “noise” can interfere with other electrical equipment in the vicinity of the drive and can be especially detrimental to the operation of sensors. Although filters can be used to remove the noise, they often reduce the speed of the sensing signals.

These differences in performance are a result of the operating principles that each drive employs. A PWM drive delivers a specified amount of voltage to the motor by switching the voltage across the transistors on and off at a very high frequency — typically in the range of 20 kHz. (When the voltage is switched on, the transistors are said to be saturated.) This switching creates pulses, and the switching frequency controls the width of the pulses — hence, the term “pulse-width modulation.” The ratio of on-time to off-time during switching determines the average voltage supplied to the motor.

In a linear amplifier, the transistors are always on to some degree, allowing voltage to flow continuously through the transistors and to the motor, rather than being switched on and off. This makes matching the amplifier’s output voltage to the motor and application requirements even more critical and, in some cases, more complex, than with PWM drives. Factors such as the motor’s torque constant, back EMF, and resistance all play a role in determining the required output voltage from a linear amplifier.

Because there is always some voltage flowing through the transistors, linear amplifiers experience significant power dissipation, and in turn, relatively low efficiency — typically in the range of 50 percent, although it can be lower. (In contrast, PWM drives often have efficiencies of 90 percent or better.) Of course, the power is dissipated as heat, which means a linear amplifier needs a large heat sinks to protect the transistors, increasing size and cost and often restricting their practical applications to those with power requirements of 100 W or less.

Despite these drawbacks, the lack of power switching gives linear amplifiers the benefit of very low audible noise and virtually no EMI. They also have a higher current loop bandwidth, and no dead band at the zero current crossing.

Linear amplifiers provide much better position stability than can be achieved with PWM drives.
Image credit: Trust Automation

Drives that exhibit a dead band — as PWM drives do — cannot accurately provide the low levels of current required as the motor switches from positive to negative torque (or velocity) — i.e., at the “zero crossing” of the current waveform. This makes it difficult to control very small movements, which can cause dithering and long settling times. Unlike PWM drives, linear amplifiers don’t experience a dead-band, which allows them to provide much better velocity control and settling characteristics.

A dead band is essentially a flat spot in the current waveform at its zero crossing.
Image credit: Electronics Tutorials

High current loop bandwidth, low EMI, and smooth motion characteristics make linear amplifiers the best choice for ultra-high positioning applications. They’re often used in precision stages to drive linear motors or voice coil actuators in semiconductor, medical, and optical equipment.

The term “linear” amplifier has nothing to do with whether the motor being driven is a linear or rotary version. Linear amplifiers can be used on both linear and rotary motors, either brushed or brushless.

Feature image credit: Bardac Corporation

When do you need a soft starter for an AC motor?

November 21, 2018 By Danielle Collins Leave a Comment

Image credit: WEG Electric

The traditional method of starting an AC induction motor “across the line” results in full voltage, current, and torque being applied immediately when the motor is started, and likewise, being removed immediately when the motor is stopped. While this is the most simple starting method, the high inrush current (often 6 to 7 times the motor’s rated current) and peak starting torque can damage the motor, driven equipment, and product. Across the line starting also causes high peak power demand, which can trigger peak demand fees from the utility company.

A soft starter can eliminate these problems by gradually increasing voltage to the motor terminals during startup, providing a controlled ramp-up to full speed. This lowers inrush current and controls starting torque, reducing mechanical shocks to the system and to the product.

In a soft starter, three pairs of SCRs control voltage to the motor during startup.
Image credit: WEG Electric

Soft starters are also known as reduced voltage soft starters (RVSS).

A soft starter relies on three pairs of SCRs (silicon controlled rectifiers) — one pair for each phase of power — that are applied gradually for portion of each voltage phase, limiting the voltage provided to the motor. In turn, current is reduced proportionally to the reduction in voltage. Torque, however, is proportional to the square of the voltage, so even a small reduction in voltage results in a large reduction in torque. For example: a 50 percent reduction in voltage yields a 50 precent reduction in current and a 75 percent reduction in torque.

Where:

T₂ = Torque at reduced current/voltage

T₁ = Torque at locked rotor current

I₂ = Reduced current

I₁ = Locked rotor current

V₂ = Reduced voltage

V₁ = Full voltage

Once the motor is up to speed, the soft starter is bypassed and the motor is connected across the line, allowing full power to the motor terminals. Soft starters introduce almost no harmonics into the system and typically have efficiencies of 99 percent or better.

A soft starter (solid-state starter) allows current to be limited (top) during motor starting. The corresponding torque reduction (bottom) is proportional to the square of the reduction in voltage.
Image credit: Eaton Corporation

It’s important to note that a VFD (variable frequency drive) can provide the same controlled starting and stopping functions that a soft starter provides, albeit in a different way — by varying the frequency of the voltage, rather than by controlling the amount of voltage, supplied to the motor. VFDs offer other benefits over soft starters, the most significant being the ability to control motor speed throughout the operating range. VFDs can also provide holding torque (full torque at zero speed), which is critical in applications such as elevators and cranes.

For applications such as conveyors and fans that require speed and torque control or current limiting during starting and stopping — but run at constant speed otherwise — soft starters provide a simple, economic solution in a small footprint.

What is DC injection braking and how does it compare with other methods?

November 15, 2018 By Danielle Collins Leave a Comment

Many variable frequency drives (VFDs) include DC injection braking functionality.
Image credit: Galt Electric

AC induction motors excel at driving high-inertia loads at high speeds — in fans, saws, conveyors, and mills, for example — and variable frequency drives make it possible to match the motor speed to the application requirements by varying the frequency of the supplied voltage.

But when quick stops are needed — whether for safety reasons or to prevent wasted time and lost productivity waiting for the load to come to a standstill — high speeds and high load inertia make it difficult to brake the motor and stop the load.

In an AC induction motor, three-phase AC power is fed to the stator windings, creating a magnetic field that rotates. This magnetic field induces a current and a corresponding magnetic field in the rotor. The interacting magnetic fields of the rotor and stator cause the motor to turn.

DC injection braking works just as its name implies — by injecting DC voltage into the motor windings. Before DC injection braking can begin, the AC power to the motor stator must be disconnected — typically by the opening of a relay. In turn, a relay controlling motor braking closes, allowing DC voltage — sourced by the DC bus — to be applied to the windings. To prevent the braking current from exceeding the drive and motor ratings, circuitry in the VFD or in an external braking module controls the amount of voltage applied.

DC injection braking begins when AC voltage is removed (S1 opens) and DC voltage is injected into the windings (S2 closes).
Image credit: KB Electronics, Inc.

When DC current is applied to the motor windings, it creates a fixed (rather than rotating) magnetic field. Braking action is produced by the rotor working to align to this stationary field. The higher the DC current, the stronger the braking force.

The energy generated during braking is dissipated as heat by the motor (particularly the rotor) and the controller, so thermal limitations of these components dictate how much braking current can be applied and the amount of time for which it can be applied before overheating occurs. If DC injection braking is used frequently, the additional heating created during braking must be taken into account when sizing the motor.

Although DC injection braking can be used to hold a load stationary, it’s not generally recommended due to heat generated in the motor. And because DC injection brakes require a constant power supply, they’re not considered fail-safe devices.

DC injection braking is just one of several electrical methods of bringing an AC induction motor to a stop. Two other forms of braking — dynamic braking and regenerative braking — convert mechanical energy generated as the rotor slows down into electrical energy.

During motor starts and stops, or when the load is overhauling, an AC induction motor functions as a generator and produces electrical energy from mechanical energy. This electrical energy can be fed back to the AC power source.
Image credit: Bonitron

In a dynamic braking system, this electrical energy is released as heat through a voltage regulated resistor. In regenerative braking, this electrical energy is fed back to the power supply or to a common DC bus. Dynamic braking is best for applications that require only periodic braking without high heat dissipation demands, while regenerative braking is best for applications with frequent stops and starts or overhauling loads.

A drawback of both dynamic braking and regenerative braking is that the braking force decreases as the motor (rotor) slows down. DC injection brakes are often used in conjunction with dynamic or regenerative braking systems to provide the final braking power required to fully stop the motor and load. And because DC injection brakes can cause thermal problems for the motor and drive, the use of dynamic or regenerative braking in the beginning, together with DC injection braking at the end of the stop, reduces the risk of overheating while providing fast, complete stopping for high-inertia, high-speed AC induction motor applications.

What do IP ratings really mean, and how do they differ from NEMA ratings?

November 9, 2018 By Danielle Collins Leave a Comment

Image credit: Kollmorgen

Electrical enclosures, such as those for motors, sensors, and HMIs, are often given what is known as an IP rating, consisting of the two letters, “IP,” followed by two numeric digits — IP65, for example. This IP rating indicates the amount of protection the enclosure provides against the ingress of solid particles and liquids.

Unlike other designations that are often applied to industrial equipment, such as “high torque,” or “waterproof,” IP ratings are specific and internationally accepted. Both the rating system and the testing process are defined by the International Electrotechnical Commission in standard IEC 60529.

The initials “IP” are often taken to mean “Ingress Protection,” but according to IEC 60529, the correct term is “International Protection.”

Decoding the IP rating system

The first numeric digit in the IP rating specifies the protection level against foreign objects, based on the size of the object (12 mm versus 1 mm, for example). The higher the number, the better the protection, with the maximum rating being 6, which indicates a dust-tight enclosure. An enclosure that meets a stated degree of protection against solid objects must also meet all the lower degrees of protection. For example, an enclosure rated IP4x must also meet IP3x, IP2x, IP1x, and IP0x requirements.

The second numeric digit specifies the protection level against the ingress of liquids, based on the amount of liquid and the direction of its approach to the object. The test to determine protection against liquids is time-based, and where applicable, includes specification of nozzle size, distance from object, and delivery pressure.

Image credit: Techathlon

It’s important to note that for protection against liquids, an enclosure must meet all the protection requirements below its rated designation, up to and including level 6 protection. Enclosures rated IP-7 and IP-8 do not have to comply with IP-5 and IP-6 requirements for water jet exposure.

If a device has not been tested or rated for one of the criteria, that digit is replaced with an “X.” For example, IPX4.

An important extension of the IP ratings comes from the DIN standard 40050-9 (which has been rolled into the ISO standard 20653:2013). This DIN standard adds an additional letter, “K,” to indicate environmental sealing. This additional specification applies only to IP6- ratings, which means the device must be dust-tight before the environmental sealing (“K”) designation can be applied.

An IP6-K rating, such as IP69K, means the device can withstand high-pressure cleaning and steam cleaning, with the test consisting of 80° C water delivered at pressures of 8 to 10 MPa (80 to 100 bar) at a rate of 14 to 16 L/min, with the nozzle located 10 to 15 cm from the device at angles of 0, 30, 60, and 90 degrees for 30 seconds each. Food processing and pharmaceutical applications often require electrical equipment that meets IP69K standards, due to the use of high-temperature, high-pressure liquids and steam for cleaning.

How are NEMA enclosure standards different?

NEMA — the National Electrical Manufacturers Association — also provides a standard, referred to as NEMA 250-2014, that defines an enclosure’s ability to provide environmental protection.

While the NEMA and IEC standards have the same general purpose, the protection requirements and test standards specified by NEMA 250 are, in some cases, more rigorous. For example, the NEMA 250 standard addresses environmental conditions such as corrosion, icing, oil, and coolants — none of which are addressed by the IEC 60529 standard.

Protection ratings in the NEMA 250 standard are categorized by whether the equipment is constructed for indoor or outdoor use, and whether it is applied in non-hazardous or hazardous locations. For example, NEMA enclosure Types 1, 2, 4, 5, 6, 12, and 13 are applicable to enclosures constructed for indoor use in non-hazardous locations. Types 3, 4, and 6 apply to enclosures constructed for outdoor use in non-hazardous locations. (Note that there is some overlap between indoor and outdoor use in Types 4 and 6.) Types 7, 8, 9, and 10 apply to enclosures in hazardous locations.

The table below is a simplified description of the NEMA enclosure ratings. For the full definitions and specifications, see the NEMA Enclosure Types document.

NEMA Enclosure Types Guide
Image credit: Marshall Wolf Automation

Can IP and NEMA enclosure ratings be cross-referenced?

In some cases, it is possible to convert NEMA Type ratings to IEC IP ratings, but because NEMA ratings include requirements not covered by IEC, it’s not possible to convert an IP rating to a NEMA Type rating, as the IP rating would not cover the same conditions as the NEMA rating.

The chart below, provided by NEMA, can be used as a guideline for converting NEMA Type ratings to IEC IP ratings.

A shaded block in the “A” column indicates that the NEMA Enclosure Type exceeds the requirements for the respective IEC 60529 IP First Character Designation. The IP First Character Designation is the protection against access to hazardous parts and solid foreign objects.

A shaded block in the “B” column indicates that the NEMA Enclosure Type exceeds the requirements for the respective IEC 60529 IP Second Character Designation. The IP Second Character Designation is the protection against the ingress of water.

Feature image credit: Unmanned Systems Source

What is an LVDT (linear variable differential transformer)?

November 3, 2018 By Danielle Collins Leave a Comment

A linear variable differential transformer (LVDT) is an absolute measuring device that converts linear displacement into an electrical signal through the principle of mutual induction. Its design and operation are relatively simple, providing extremely high resolution in a device suitable for a wide range of applications and environments.

The main components of an LVDT are a transformer and a core. The transformer consists of three coils — a primary and two secondaries (S1 and S2) — wound on a hollow form, which is typically made of glass-reinforced polymer. The coils are arranged such that the primary coil is located between the two secondary coils, which are symmetrical and wound in series but in opposite directions (referred to as series-opposed winding).

The core is made of magnetically permeable material and moves freely inside the bore of the transformer. A non-ferromagnetic shaft, or push rod, is coupled to the core and connects to the object being measured.

Image credit: Honeywell International

When voltage is applied to the primary winding, the resulting flux is coupled to the secondary windings by the core. This induces voltages (often denoted E1 and E2) in each of the secondary windings. The differential voltage in the secondary windings determines the distance moved, and the phase of the voltage indicates the direction of movement.

Here’s how it works…

The series-opposed winding of the secondary coils means that when the core is at the center of the transformer (equidistant between the two secondary coils), the induced voltages have equal amplitude but are out of phase by 180 degrees. Thus, the induced voltages cancel each other, and the output voltage is zero. (This is often referred to as the null point.)

When the core moves to one side — toward S1 for example — the secondary coil on that side becomes more strongly coupled to the core, causing the induced voltage (E1) of that secondary to be higher than the induced voltage (E2) of the opposite secondary (S2). The differential voltage output (E1 – E2) determines the amount of movement.

The amplitude of the differential output voltage determines the distance traveled, and the phase of the output voltage indicates the direction traveled.
Image credit: TE Connectivity

The induced voltage (E1) of the first secondary coil is in-phase with the primary voltage, indicating the direction of movement. Conversely, when the core moves to the other side of the transformer, the induced voltage (E2) of that secondary coil is out of phase with the primary voltage, indicating movement in the opposite direction.

The output of an LVDT is a direct and linear function of the input across its specified measuring range, although linearity falls off as the core reaches or exceeds the ends of its range. However, it is possible to use an LVDT beyond its specified range, in some cases, with a pre-defined table or polynomial function to compensate for the nonlinearity.

LVDT output is a direct, linear function of the input voltage up to the device’s specified measuring range. Beyond this point, linearity begins to fall off.
Image credit: TE Connectivity

An LVDT contains no electronics, but external electronics — referred to as a signal conditioner — include an oscillator to generate the drive signal, along with a demodulator, an amplifier, and a low-pass filter to convert the AC output voltage to a DC signal. Because they rely on the coupling of magnetic flux, LVDTs have almost infinite resolution, limited only by the noise in the signal conditioner. Similarly, repeatability is extremely high — typically less than 0.1 percent of the measurement range. Common measurement ranges are from ± 0.25 mm to ± 750 mm.

Signal conditioning electronics can be contained inside the LVDT housing. This configuration is typically referred to as a DC LVDT because the primary coil is supplied with DC voltage. Although internally-housed electronics reduce complexity, DC LVDTs have lower resistance to shocks, vibrations, and temperature extremes than traditional AC LVDTs.

LVDT devices are extremely robust, since there is no physical contact, and therefore no friction or wear, between the moving core and the transformer bore. The transformer is typically encapsulated with epoxy to protect against contamination and moisture, and the housing can be made from a wide variety of materials — from stainless steel to nickel alloys or titanium.

Typical applications include tensile test and other material testing devices, load cells, and weighing devices. LVDTs are also used to measure displacement in hydraulic cylinders and actuators.

What are chain-on-edge conveyors and where are they used?

October 18, 2018 By Danielle Collins Leave a Comment

Conveyors are the backbone of many factories, moving parts and materials through assembly or processing stations via chains, rollers, belts, or pallets. Most conveyor designs hold the part stationary, in a given orientation, as it moves down the line. And in many processes, maintaining a fixed orientation is important — when a part is being inspected, for example, or being delivered to a robot for assembly. But when the application calls for the part to change orientation between one station and the next, or even to rotate as it’s being conveyed, a chain-on-edge conveyor is often the best option.

Chain-on-edge conveyors allow parts to rotate as they’re conveyed.

Spindles attached to the chain allow products to rotate as they’re conveyed.
Image credit: BGK Finishing Systems

A chain-on-edge (COE) conveyor is essentially a single-strand chain conveyor that has been turned 90 degrees, so that it runs on its side. The chain-on-edge design typically uses a roller chain that runs in a channel and is supported by plates. The chain flexes along the horizontal axis, allowing this style of conveyor to make horizontal turns. Vertical curves (height changes) are also possible with the chain-on-edge design, but the curves must be gradual. These turning capabilities make chain-on-edge conveyors much more versatile than traditional chain conveyors.

The key to product rotation in a chain-on-edge conveyor is the use of spindles attached to the chain. The spindles can be designed to rotate freely, to rotate and stop at preset positions (90 and 180 degrees, for example), or to stop at custom positions. Stationary spindles are also an option, and are often used for smaller parts that need to be transported with access to all sides, but not necessarily rotated, during transport.

Chain-on-edge conveyors are sometimes referred to as “spindle conveyors.”

Although their unique feature is the ability to rotate parts during transport, chain-on-edge conveyors are also used for transporting heavy loads that don’t rotate, but that require full access to the outer sides and top of the part. In these applications, the load is carried on a truck, or cart, attached to the chain. For large or asymmetrical loads, the chain is accompanied by external tracks, or outriggers, that help support and guide the load.

A chain-on-edge conveyor with outrigger tracks to help support and guide the load.
Image credit: Central Conveyor

Rider plates attach to the chain, and pusher dogs — mechanical latch-type devices that engage and disengage with the trucks — attach to the rider plates. In some chain-on-edge designs, pusher dogs can be used to facilitate product accumulation or transfer from one chain to another.

Mechanical latches, referred to as “pusher dogs,” engage and disengage with transport trucks and can allow products to accumulate or transfer from one chain to another.
Image credit: Jervis B. Webb Company

Applications that call for a product to rotate during transport including painting, coating, curing, cleaning, baking and drying. These applications are found extensively in the automotive industry, but virtually any product with an outer surface that has been painted, coated, or cured has likely been transported by a chain-on-edge conveyor.

When used in painting and coating applications, chain-on-edge conveyors are typically enclosed in a protective housing with a covering that prevents contamination of the chain and internal components.
Image credit: Precision Conveyor Coating Technologies, Inc.

Feature image credit: Precision Conveyor Coating Technologies, Inc.

Control Techniques announces new servo drive

October 15, 2018 By Danielle Collins Leave a Comment

Control Techniques, part of the Nidec group of companies, has revealed its new generation of advanced servo drive technologies.

The new Digitax HD servo series delivers ultimate motor control performance and flexibility from a uniquely compact package. Targeting high axis count automation systems, Digitax HD provides all of the benefits of a modular system with a common DC bus, with standalone drive flexibility. The drives’ wide power range provides 6.2 – 451.4 lb-in (0.7 – 51 Nm) with 3x peak torque (1.5 A – 16 A and 48 A peak).

The new series is focused on high overload, pulse duty applications but also provides continuous servo control, plus induction motor control, and is initially available with two functionality levels. The new Digitax HD servo solutions launched in the Americas on October 15 at Pack Expo.

Digitax M753 is designed as an optimized amplifier for high performance centralized control with EtherCAT integrated on-board and simple rotary switches for fast network address assignment. Alternatively, the flexible Digitax M751 base option allows design engineers to add up to two option modules from the existing Unidrive M range, such as PROFINET, Ethernet/IP, or an IEC61131 high performance motion controller for decentralized machine control.

Minimum size

For both single and multi-axis configurations, the Digitax HD series offers industry-leading compactness – the M753 EtherCAT variant is just 1.6 inch (40 mm) wide – that is 5 axes across the width of a piece of paper or 7 axes across if you turn it to landscape. The drive is also designed to fit within 8 inch deep (200 mm) enclosures.

Digitax HD is the most compact 400V servo drive available in the world

Its patented Ultraflow™ system allows machine builders to further reduce cabinet size by up to 50 percent through expelling heat from the drive directly outside the enclosure. This approach offers the further benefit of enabling drives to be stacked without the need for a large air channel between them.

Maximum performance

High dynamic applications will benefit immensely from Digitax HD’s 300 percent peak performance pulse-duty overload capabilities, along with its 62 μs current loop and 16 kHz switching frequency. Its flexible speed and position feedback interface supports a wide range of feedback technologies, from robust resolvers to the latest single cable digital encoder technologies.

Quick and easy installation

Digitax HD boasts a wealth of features and accessories designed to make installation and commissioning as easy as possible. Features include easy-access pluggable connectors and a dedicated multi-axis paralleling kit for rapid installation; integrated braking resistor and electronic motor name plate for faster setup; and quick commissioning using the Unidrive M Connect PC tool or an optional SD card. Machine Control Studio provides a flexible and intuitive IEC61131 environment for programming automation and motion control features.

Flexibility

The Digitax HD servo series flexibly adapts to your architecture of choice, be it centralized motion control, distributed intelligence, or any combination of the two. Support for all main industrial field-buses guarantees easy integration into any production line.

Complementary motor line-up

Working in tandem with the Digitax HD series, delivering class-leading performance with a wide torque range, up to 750 lb-in (85 Nm) with 3x peak, rated speeds from 1,000 to 6,000 rpm, several inertia levels, and a broad selection of feedback options, Unimotor hd offers the perfect fit for high dynamic applications.

Control Techniques

What is meant by the term General Motion Control?

October 11, 2018 By Danielle Collins Leave a Comment

There are numerous interpretations of what the motion control market entails in terms of products included and industries served, but there are some commonalities among the various definitions.

First, a motion control system includes at least three basic components — a motor, a drive, and a controller. Second, motion control systems are primarily used in discrete industries such as packaging and semiconductor manufacturing, as opposed to process industries such as chemical manufacturing and power generation.

No matter how it’s defined, the motion control market is huge, ranging anywhere from $9 billion to $12 billion, depending on which products and industries are included. With very large industries, the number of market players and drivers add significant uncertainty and complexity to everything from product planning to market analysis. One way to address this complexity is to divide the market into smaller segments, based on similar product groups or industry categories. Take, for example, the passenger vehicle market. Most passenger vehicle manufacturers and industry analysts recognize at least three subsegments of the market — cars, trucks, and sport-utility vehicles (and most break the market into even smaller segments).

Similarly, to address the size and complexity of the motion control market, manufacturers and analysts have divided the market into two subsegments: general motion control (GMC) and computer numerical control (CNC).

Most industry statistics show that general motion control (GMC) accounts for just over 50 percent of the overall motion control market, while computer numerical control (CNC) accounts for just under half.

The basic function of a general motion control system is to control the acceleration, speed, and/or position of a single motor or of multiple coordinated motors. From an OEM or end-user perspective, GMC systems provide general-purpose, coordinated motion. They are typically used in the industrial automation market, but exclude military, aerospace, and consumer products applications.

Semiconductor manufacturing is one of the key industries that general motion control systems serve, along with packaging, material handling, and a host of others.

In contrast, computer numerical control (CNC) systems provide multi-axis coordinated motion and are typically used for contoured moves that require interpolation. CNC systems are often designed to meet the specific requirements of the machine tool industry, although they can be used in other industries.

CNC systems are often tailored to the specific requirements of the machine tool industry.
Image credit: Gebr. Heller Maschinenfabrik GmbH

Note that GMC systems can also be used in machine tool applications, especially for processes such as loading/unloading parts and for coarse positioning moves not involved with actual material processing.

One thing that is not widely agreed upon among industry analysts and manufacturers is which components are included in a general motion control system. Case in point, ARC Advisory Group considers the components that make up a GMC system to be the motor, drive, controller, and any integrated feedback devices. Siemens, a leading manufacturer of motion control components and systems, includes two additional components in their definition: software that is developed specifically for the application (which, in some cases, would be included in the controller in ARC’s definition) and the mechanical system — belt, chain, ball screw, rack and pinion, etc. — that transmits work to the load.

Most experts agree that a GMC system consists of a motor, drive, controller, and feedback. Siemens’ definition of a GMC system also includes the application-specific software and the mechanical system.
Image credit: Siemens Industry, Inc.

It is recognized, however, that general motion control systems are most often based on servo motors and drives, although some manufacturers and analysts consider stepper-based systems to be part of the GMC market. (It could be argued that open-loop stepper systems — which are by far more common than closed-loop steppers — do not qualify as GMC systems since they don’t rely on a feedback device.) The most common definitions of general motion control also include both stand-alone drive amplifiers and motor-integrated drives, as well as stand-alone, PLC-based, and PC-based motion controllers.

Don’t confuse the term “general motion control,” as described here, with the term “generic motion control,” which is a software platform from B&R Automation.