Motors - Motion Control Tips

Servo motor offers increased torque, speed and efficiency in compact footprint

May 16, 2019 By Miles Budimir Leave a Comment

Kollmorgen’s AKM2G synchronous servo motors are the next generation of its AKM motor product family, and provide increased capabilities for demanding applications. The higher torque density of the AKM2G allows OEMs to substantially increase machine performance without increasing motor size. Greater flexibility and wider speed range enables machines to run faster, move heavier loads, and increase throughput. The AKM2G is also highly efficient, offering lower energy consumption and costs compared to competitive motors.

Key benefits include:

Smaller footprint – With average continuous torque increases of 30 %, AKM2G significantly reduces the space dedicated to motors and mechanical components without sacrificing performance. Newly available space allows for additional production capacity, and smaller machines can allow operators to run multiple machines at one time.

Increased torque – The higher torque density of the AKM2G allows machines to do more and increases throughput. With six sizes and performance levels between 0.3 and 10 kW, the AKM2G helps existing machines produce new variants such as larger-size product.

Wider speed range – With rated speeds up to 8,000 rpm, the AKM2G allows existing machines to run faster, change-over quicker and produce more when production demands surge.

Greater flexibility – The AKM2G supports a wider array of feedback, brake, thermal sensor, and shaft seal options, allowing OEMs maximum flexibility in machine design and compatibility with current machine configurations. Now available for low voltage and dc applications from 24 to 96 V providing optimum high-performance solutions for portable and mobile applications including operation from battery systems.

Higher efficiency – The AKM2G builds on the AKM’s industry-leading efficiency, bringing models to as much as 98 % efficient. OEMs can meet energy efficiency parameters that are becoming requirements in multiple markets.

For more information visit www.kollmorgen.com.

When to use gears to change the inertia ratio of a motor-driven system

May 15, 2019 By Danielle Collins Leave a Comment

In any system where a motor drives a load to achieve precise positioning, velocity, or torque, the ratio of the load inertia to the motor inertia plays a significant role in determining the motor’s ability to effectively and efficiently control the load, especially during acceleration and deceleration portions of the motion profile.

In this context, the inertia we’re referring to is mass moment of inertia (sometimes referred to as rotational inertia), which is an object’s resistance to change in rotational speed. An object’s mass moment of inertia is determined by its mass and geometry — specifically, the radius between the object’s center of mass and the point around which the object rotates.

Adding a gear set or gearbox between the motor and the load can improve the load-motor inertia ratio.
Image credit: Omron Industrial Automation

If the inertia of the load is significantly higher than the inertia of the motor, the load will essentially try to “drive” the motor, and the motor will have a difficult time achieving the desired position (or speed or torque). In an attempt to control the load, the motor will draw higher current, which decreases efficiency and increases wear on the motor and electrical components.

On the other hand, if the inertia of the motor is significantly higher than inertia of the load, it’s likely that the motor is oversized, which has negative implications throughout the system — including higher initial cost, higher operating cost, larger footprint, and the need to oversize other components, such as mounting hardware, couplings, and cables.

If the inertia ratio is too high — that is, if the load inertia is much higher than the motor inertia, causing problems with positioning accuracy, settling time, or control of velocity or torque — the load inertia that is seen by, or reflected to, the motor can be decreased by adding a gear set or gearbox between the motor and the load.

J_L = inertia of load reflected to motor

J_M = inertia of motor

Adding a gear set or a gearbox to a motor-driven system reduces the load inertia by the inverse square of the gear ratio, meaning that even a relatively low gear ratio can have a significant effect on the inertia ratio.

J_L = inertia of load reflected to motor

J_D = inertia of drive (ball screw, belt, rack & pinion)

J_E = inertia of external (moved) load

J_C = inertia of coupling

J_G = inertia of gear set or gearbox

i = gear ratio

Note that the inertia of the gear set or gearbox (J_G) is added to the load inertia, but its effect is typically small compared to the reduction provided by the gear ratio.

In addition to optimizing the load-motor inertia ratio, gearboxes are often used in motion control applications to increase the torque delivered to the load from the motor, but they also decrease the rotational speed delivered to the driven component from the motor, by an amount equal to the gear ratio. This is why gearboxes are often referred to as “gear reducers” or “speed reducers.”

In other words, if a motor running at 1200 rpm is driving a load through a 3:1 gearbox, the rotational speed delivered to the load will be 400 rpm (1200 ÷ 3). This reduction in speed can enable the system to operate at a more favorable location on the motor’s speed-torque curve.

Although it is possible to use a gearbox or gear set that is configured to reduce torque (and increase speed), in motion control applications, a more typical solution would be to choose a smaller motor.

Feature image credit: M. M. Nazari

What is disturbance rejection in motion control?

May 13, 2019 By Danielle Collins Leave a Comment

One of the key functions of a motion controller is to create the trajectories the motor follows in order to reach the target position (or velocity or torque). As the motor turns, the controller processes feedback from the encoder and compares the actual position of the motor with the desired position. If there are any deviations between the actual position and the desired position, the controller issues commands to correct the error.

Deviations can be caused by inaccuracies in the mechanical components (backlash in screws, compliance in connecting elements, or errors in mounting surfaces) or by unknown disturbances — often in the form of unexpected forces on the system that cause the position, velocity, or torque to rise or fall sharply and unpredictably.

The motor’s ability to follow the given trajectory and achieve the desired position is tracked and managed by the controller through a function known as command tracking or reference tracking. (When the controller is monitoring a process variable, such as temperature or fluid level, rather than the position, speed, or torque of a motion control system, this function is referred to as setpoint tracking.)

Each gain in the PI (proportional-integral) or PID (proportional-integral-derivative) control loop affects the system’s reference tracking. In addition, feedforward control, a proactive control method that predicts the system’s error and injects commands into the control loop to minimize the error, is often used to improve reference tracking and further minimize the deviation between the commanded position and the actual position of the motor.

To address unexpected forces that cause the motor to move away from the target value, the controller uses a function known as disturbance rejection, which processes the disturbance and provides commands that correct for these unknown forces or conditions.

Block diagram for a PID controller with an input disturbance (T_d).
Image credit: Quanser Inc.

In control tuning, the proportional gain (k_p) determines the amount of disturbance rejection. This makes sense because the proportional gain issues an error correction signal that is directly proportional to the error. So when a disturbance occurs, causing the motor to deviate from the desired state, the proportional gain outputs a correction signal to bring the motor back toward the desired state. In theory, the higher the proportional gain, the better the disturbance rejection. But in real-world applications, the maximum value of proportional gain that can be used without causing instability is limited by the system bandwidth and phase margin.

A controller can be tuned to balance the reference tracking and disturbance rejection functions, as shown here, or to favor one or the other.
Image credit: MathWorks Inc.

Motion controllers often use both functions — reference tracking and disturbance rejection — to provide accurate, steady-state performance and to reduce sensitivity to changing or unexpected loads. However, there are tradeoffs when both functions are used: the lower the overshoot and settling time for reference tracking, the more sluggish the disturbance rejection will be, and vice-versa. Tuning the controller involves finding the appropriate balance between the overshoot and settling time of the reference tracking function and the response time of the disturbance rejection function.

Compact step motors with high torque for space-limited applications

May 10, 2019 By Miles Budimir Leave a Comment

Applied Motion Products offers compact step motors in NEMA sizes 8, 11 and 14 for applications with limited space including medical devices, 3D printers, analytical and medical instruments, robotics and others.

These lightweight and low-cost motors offer high torque up to 22 oz-in. at low speed. Even while sized smaller, the compact step motors operate with high step accuracy and resolution as well as low vibration and noise – important factors in machinery lines and medical equipment. The compact step motor line includes:

NEMA size 8 in two lengths (1.24 in. and 1.85 in.) and holding torque up to 4.53 oz-in.
NEMA size 11 in two lengths (1.22 in. and 2.05 in.) and holding torque up to 14.16 oz-in.
NEMA size 14 in two lengths (1.02 in. and 1.57 in.) and holding torques up to 25.53 oz-in.

These hybrid-type small motors offer the highest torque density in their frame size. With a 1.8˚ step angle and being RoHS compliant, units are available in both single and double-shaft versions. To address customers requirements for specific connectors and couplings, Applied Motion Products provides its compact motors with customized cable and connector assemblies and a variety of options including flats, thru-holes, custom lengths, and more.

Applied Motion Products also offers a full complement of stepper drives that optimize the torque and speed performance of its compact step motors while providing smoother and quieter operation. For basic step and direction control applications, operators can set up the miniature STR3 stepper drive with just a screwdriver. A new STF stepper drive family offers on-board programming and network communications. All software tools for these drives are free and easy-to-use. Q Programming provides the option to store motion profiles on STF drives and execute profiles in stand-alone mode or via a digital I/O.

For more information visit www.applied-motion.com.

Haydon Kerk Pittman adds 42-mm motor to IDEA Motor series

May 9, 2019 By Miles Budimir Leave a Comment

Haydon Kerk Pittman, a business unit of AMETEK Advanced Motion Solutions, announces the latest addition to its line of brushless dc motors: the EC042B IDEA Motor Series. The new motor is 42-mm in diameter and integrates a high-torque, precision brushless servo motor with an IDEA Drive in a single compact unit. The IDEA Motor enables distributed control without the use of a costly PLC or external motion controller.

The EC042B IDEA Motor is offered in three motor lengths with continuous torque up to 0.15 Nm with integrated inputs, outputs, encoder, and RS-485 communication. The GUI (Graphic User Interface) integrates a trapezoidal and S-curve trajectory generator with a movement profile plotter. The IDEA Motor can store and execute multiple programs with I/O driven nested, prioritized, and vectored interrupts as well as polled I/O for autonomous real-time control. Users familiar with the current IDEA Drive GUI will recognize the layout and appreciate the expanded features of the GUI.

Haydon Kerk Pittman standard PLG42S and PLG52 gearboxes are available as factory options. Torque ratings for PLG42S are as high as 14 Nm while the PLG52 torque rating achieves up to 24 Nm. The wide range of reduction ratios and torque capabilities enable optimized performance of the EC042B IDEA Motor for highly specialized or unique motion applications. These applications include lab automation, medical devices, communications equipment, semiconductor processing equipment, aerospace systems and many other applications where precision motion and compact packaging are critical.

For more information visit www.haydonkerkpittman.com.

Dunkermotoren BG series motors now compatible with Siemens SIMATIC MICRO-DRIVE servo drive system

May 7, 2019 By Miles Budimir Leave a Comment

As part of a product partnership with Siemens, Dunkermotoren BG series motors are now also available in specific versions compatible with the new Siemens SIMATIC MICRO-DRIVE servo drive system. The series BG 45, BG 65(S), BG 75 and BG 95 are 24 to 48 V brushless dc motors with power ranges from 20 to 1,000 W.

The simple integration of the SIMATIC MICRO-DRIVE servo drive system into the SIMATIC world significantly shortens engineering time. The integration into Siemens automation technology is possible via the TIA portal and simplifies commissioning and service. Communication is via PROFINET IRT with PROFIsafe and PROFIdrive profiles. The new Safety Integrated Function SLT (Safely Limited Torque) ensures a limited torque by monitoring the motor current during operation.

Smart components in the motor, together with a patented data transmission system, set the controller to a preset state after it is connected to the motor. It eliminates cumbersome drive tuning and parameterization of the controller control loops.

A modular system allows the motors to be individually adapted and matching planetary and right-angle gears and brakes complete the comprehensive portfolio.

For more information, visit www.dunkermotoren.com.

New brushless motor with integral drive from Allied Motion

May 2, 2019 By Miles Budimir Leave a Comment

Allied Motion Technologies’ new EnduraMax 75i Series is a 75-mm diameter brushless dc motor with an all-digital integrated drive. The EnduraMax 75i is capable of controlling torque, speed, and position in a wide range of commercial and industrial applications including: AGV vehicle traction or steering, medical patient-handling equipment, rotary/linear actuators, pumps, mobile HVAC blowers, and material handling systems. Compared to brush dc motors, the cost-effective EnduraMax 75i features quieter operation and longer life without the need for brush maintenance, making it suitable for equipment modernizations and new designs.

The EnduraMax 75i offers three standard stack lengths with continuous rated power up to 370 W, continuous rated torque up to 1.3 Nm (190 oz-in.), and rated speed of up to 5,150 rpm. The 12, 24, or 48 Vdc winding voltage choices make the EM75i suitable for battery-powered applications. Command inputs may be: ±10 Vdc, 4 – 20 mA, or via an optional CANopen or Modbus port. Customized winding designs and voltages, shaft, and mounting options are available to meet custom application requirements.

Options include:

Integration with Allied Motion gearboxes
Stainless steel shaft
9- or 10-mm diameter shaft
Pre-made connectorized cables
Integral holding brake
Sealed ball bearings
IP67 protection level

For more information, visit www.alliedmotion.com.

AC induction motor inertia: What’s the difference between WK2 and WR2?

April 29, 2019 By Danielle Collins Leave a Comment

In any motor-driven system, the difference between the motor inertia and the load inertia will affect the system’s performance — especially its ability to accelerate the load quickly and efficiently.

While servo motors are the preferred choice for applications that specify a precise move profile, AC induction motors are often the better choice for applications where a rotating device (such as a fan, blower, or gearbox) needs to achieve a given speed within a certain amount of time and maintain that speed regardless of changes in the load.

In servo-driven motion control applications, we typically look at the inertia ratio — the ratio of the load inertia to the motor inertia — to give us an idea of how the motor will perform for the type of application and performance requirements (high acceleration, fast settling time, accurate positioning). Although inertia matching is less critical for induction motor applications than for servo-driven systems, inertia still plays an important role in the sizing and selection of an AC induction motor. This is because with rotating loads, the required motor torque is directly related to the inertia of the load.

T = torque required by motor

J = inertia of rotating load

α = angular acceleration of load

Note that inertia includes the inertia of the load (a fan, for example) plus the inertia of the motor and any other rotating components (such as couplings or pulleys) between the motor and the load.

Two definitions of inertia for AC induction motors

In motion control applications, inertia is generally given as J (as shown in the equation above) and is defined as “mass times radius squared.” However, in many rotating equipment applications, inertia is given as either WR² or WK² and is defined as “weight times radius squared.”

Notice that the inertia equations for induction motors use weight (which is a force) rather than mass. Also notice that the distance (radius) can be specified as either “R” (WR²) or “K” (WK²). R is the radius of the object, from its center to its outer edge. K is the radius of gyration, which is the distance from the point around which the object rotates, to the point at which the mass can be considered to be concentrated.

These expressions for inertia — WR² and WK² — are often used interchangeably, although R (radius) and K (radius of gyration) are rarely the same values. Here’s why…

If a hollow cylinder with extremely thin walls rotates around its axis, it’s reasonable to assume that the cylinder’s mass (weight) is concentrated around the outside circumference. So the radius of gyration for the thin-walled cylinder will be measured from the center to the outside edge of the cylinder. Thus the radius of gyration, K, is equal to the radius of the cylinder, R.

If a hollow cylinder has very thin walls, the mass can be assumed to be concentrated at the outer circumference of the cylinder.

However, if the cylinder is solid and uniform, its mass (weight) can be assumed to be concentrated at a distance of 1/2 the radius. In this case, the radius of gyration is ½ of the radius (K = ½R).

If the cylinder is solid and uniform, the mass is assumed to be concentrated at 1/2 the radius, so the radius of gyration, K, equals 1/2*R.

Using inertia to determine torque and acceleration

The distinction between these two inertia equations, WR² and WK², is important because in AC induction motor applications, inertia is used to determine the motor torque required to achieve a desired speed within a given time.

T = acceleration torque (lb-ft)

W = weight of load to be accelerated (lb)

R = radius (or K, radius of gyration) (ft)

N = change in speed (rpm)

t = time to accelerate (s)

Note: 308 is a constant that incorporates the conversions from lbf to lbm, and from rotations per minute to radians per second

Inertia can also be used to determine the time the motor will take to reach a given speed with a defined acceleration torque.

This is important because induction motors draw very high current during start-up and acceleration, and high current for an extended period of time can damage the motor.

Electric cylinders with programmable integrated motors

April 19, 2019 By Miles Budimir Leave a Comment

Captive shaft electric cylinders are now available for Lexium MDrive (LMD) integrated motor products. Quiet, clean and compact, these LMD products integrate motor, controls, and electric cylinder to deliver linear motion. And, unlike pneumatics, there is no need for compressed air, eliminating maintenance and noise issues.

Lexium MDrive products integrate 1.8° 2-phase stepper motors with onboard drive electronics, controller, and encoder which includes an absolute encoder option. Fully programmable motion controllers can communicate via EthernetTCP/IP, CANopen, or RS-422/485. Products may be operated in several modes including closed-loop, torque control, and variable current control for energy savings and reduced heating. This high degree of integration, which now includes an optional electric cylinder, can reduce machine complexity, size and cost in many motion applications.

Captive shaft electric cylinders are available with LMD products in NEMA motor sizes 17 and 23. Specifications include stroke lengths up to 24 in./610 mm, thrust up to 60 lb/27 kg, and 0.005 in./0.127 mm repeatability. The factory-mounted electric cylinders produce linear motion by coupling a coated, stainless steel acme screw with PEEK-blend nut system directly to the LMD’s motor shaft. Lexium MDrive products are assembled in our USA factory, which is certified ISO9001:2015 and ISO14001:2015.

Built to order, Lexium MDrive products with electric cylinders are available with a wide range of standard features. For more product information, visit at https://motion.schneider-electric.com/all-products/.

motion.schneider-electric.com.

Kollmorgen to feature frameless motors and gearmotors for robot design at XPONENTIAL 2019

April 18, 2019 By Miles Budimir Leave a Comment

Kollmorgen’s frameless motor solutions have empowered smaller, lighter, and faster precision robots for decades. The company will feature its latest motion technology for robot design for engineers and manufacturers at the AUVSI XPONENTIAL SHOW, April 30 to May 2, in Chicago, IL.

Throughout the show, visitors to Booth #938 can experience product demos and have the opportunity to meet with Kollmorgen experts who can provide insight on the company’s motion solutions for applications including robotic arms and joints, collaborative robots, and medical robots, as well as automated guided vehicles (AGVs) such as mobile picking/sorting robots, carts, tuggers, and self-driving forklifts.

Live demos at XPONENTIAL 2019 will include:

Robotic Gearmotor Demo: Discover how Kollmorgen’s award-winning frameless motor solutions integrate seamlessly with strain wave gears, feedback devices, and servo drives to form a light weight and compact robotic joint solution.

Frameless Motor Demo: Learn how easy it is to integrate Kollmorgen’s award-winning TBM frameless motors into any application requiring a compact, light weight, and torque-dense solution.

For more information about Kollmorgen technologies, visit www.kollmorgen.com or stop by Booth #938 during the show.