By Mark D. Hinckley, Director-Mechatronics, SKF USA Inc.
Many electro-mechanical systems can qualify as mechatronic systems. Don’t agree? Take a look at these application examples that demonstrate both the power and potential of mechatronics in action.
Mechatronics integrates mechanical and electronic technologies with application-specific software to perform a particular task. Engineers who use mechatronic components and systems do so to focus on:
• improving precision, repetition, and flexibility in movement;
• saving energy;
• expanding function;
• reducing system size, weight, and footprint;
• and minimizing both the physical and audible environmental impact.
Mechatronic designs can be as elementary as “building block” components or as sophisticated as fully integrated systems. The basic building blocks are represented by individual components, such as linear bearings and guides, bearings integrated with sensors, or ball and roller screws. You can specify these components individually in an application to help control movement, reduce friction, create a mechanism for driving linear motion, and even provide feedback on how fast equipment is rotating and in what position.
The next level combines components into a sub-system that serves as a self-contained unit to deliver more in terms of speed, strength, accuracy, reliability, or other measurement compared with basic building block components. Depending on application needs, sub-systems can include feedback devices to ascertain position or special configurations that can support structural loading. Some sub-systems will accommodate unique operating conditions while others fit more universal specifications.
Beyond sub-systems, fully integrated mechatronic systems offer “complete package” approaches that independently respond to inputs and offer real-time feedback and actions. For example, an electric parking brake engineered as a mechatronic system can receive specific input about the
current operating condition from a CANbus network. In effect, the brake “knows” when it should activate or release, based upon programming in the integrated actuator specific to that vehicle.
Our applications casebook describes a range of examples demonstrating both the power and potential of mechatronics in action.
Linear ball bearings in stretcher-mounting system
Space is scarce inside ambulances, so placing and securing a stretcher can become an issue. One mechatronic approach is to use linear ball bearings to guide the horizontal movement of a stretcher in and out of the ambulance.
The benefits here include high load-carrying capacity (to accommodate all sizes of patients), robustness and reliability, and the delivery of smooth, low-friction movement (greatly assisting EMTs). In addition, the patient bed remains tightly secured during the ride in the ambulance.
Actuators onboard “factory on wheels”
In agricultural harvesting, the combine essentially serves as a “factory on wheels.” Raw material is brought into this “factory” (harvested with the header) and proceeds through the machine where the crop (such as wheat) is separated from the chaff (waste) by the threshing mechanism. The grain from the wheat passes over a sieve mechanism where it is sifted out of the waste and collected. The chaff can then be reprocessed for complete threshing and then ejected from the rear of the combine.
Each of these processes requires movement. Since there is only one source of power (the engine), how and where to deliver that power is critical to machine function. The prerequisite for any component is that it must be mechanically robust and able to survive in the dirty and dusty environment usually encountered.
Traditional components used to perform the necessary functions include belts, chains, or hydraulics. Each presents its own challenges in delivering power to each point. Applying tailored actuators for some operations, such as the threshing mechanism, cleansing fan, secondary separation system, sieve table, and auger, can improve the overall efficiency and reliability of the machine.
Electro-hydraulic steering system for off-road vehicles
Some applications can benefit from a combination of technologies, mechatronics and otherwise. Electric steering offers flexibility and hydraulics delivers the necessary power density. Combined, the two parts replace the traditional steering column with a more ergonomic design; reduce the number of parts; simplify assembly procedures and processes; and use less space. Without the steering column operators experience less noise, better safety, and avoid hydraulic leaks in the cab.
One example of a closed-loop system integrates: a mechanical/electronic (mechatronic) steering module; a controller regulating all steering functions; high resolution kingpin bearing sensors for steering position input and actual steered wheel feedback; and an electrically actuated proportional valve. Each component “talks” to the next using CANbus protocols.
When the operator turns the wheel, a signal travels to the controller with data indicating the angle of the turn and the desired position of the wheels. The controller takes the signal and commands the proportioning valve to actuate the hydraulic cylinder, which forces the steered wheels to move to the desired position. The position sensor integrated into the kingpin measures the position of the steered wheels and returns feedback data to the controller, which are compared to the desired position input to correct any discrepancies.
This system can be programmed to adjust the number of turns for the steering wheel from lock-to-lock. Programming software governs steering sensitivity changes through vehicle speed. This feature is especially useful in operating off-road vehicles, where it is often necessary to steer quickly at lower speeds and slowly at higher speeds.
Depending on the vehicle requirements, steer-by-wire modules with a constant, non-programmable torque may be preferred. These plug-and-play systems send an electronic signal on the speed, acceleration, and direction of the steering wheel movement; and can increase cabin design flexibility and enhance operator ergonomics.
Mast height control unit for forklifts
A mechatronic system can automatically position the mast on industrial vehicles, such as forklifts. Integrated sensor bearings detect mast height and convey rotational speed and direction feedback from the ac motor.
Accurate mast height control is important when forklifts quickly move from place to place, placing or retrieving pallets or containers to and from bin locations. Through a simple readout of the mast’s height compared to a pre-programmed shelf height, sensor bearings on the mast will automatically position it to the desired height with the push of the button or the flip of a switch.
The control unit mounts on the mast to monitor its location as it travels up or down and sends a continuous signal to the controller. These signals are interpreted into precise measurements. Using either a pre-programmed mast height system or a simple digital readout system, the vehicle “knows” the height of the load and can trigger other safety systems.
For example, the forklift’s safety controls can be programmed to limit speed or turning radius, depending on the height of the load, reducing the possibility of the vehicle tipping over.
Alternatively, the safety system can prevent the mast from rising beyond a specified height when the load exceeds a predetermined weight.
Two different designs have been created for mast control units. A spring-loaded cam arrangement uses spring force to press the sensor bearing against the mast. This unit is driven directly by the moving frame of the mast. Pulley arrangement units are driven by either a wire or belt incorporated into the design of the mast-positioning system.
Both the cam and pulley control units respond directly to a designer’s need for smaller components, simpler assembly, and reliable performance.
Surgical and patient tables
Surgical equipment must meet stringent hygiene standards and perform reliably and consistently. In medical applications, electro-mechanical actuation systems have distinct advantages over conventional hydraulics. Without hydraulic fluids, there are no leaks to contaminate operating or patient rooms. The usually quiet electro-mechanical systems foster a lower stress environment for patients.
Electro-mechanical systems move telescopic pillars, or lifting columns, on surgical tables quickly and silently. For structural support, rigid aluminum profiles and precision glide pads in the columns lift offset loads without deflection. Combinations of screws and gears feature high push force capabilities and low noise levels. Telescopic pillars can satisfy other applications, including patient-positioning tables for medical imaging, treatment, and ophthalmic examination, among others that require vertical action and structural support.
As part of the system, guiding actuators extend or retract the telescopic pillars. Columns can run quietly and with minimal vibration at maximum speeds up to 45 mm/sec, depending on the model. Stroke lengths can be up to 700 mm.
Control boxes synchronize and control multiple actuators for a flexible system. The proper combination of control boxes and actuators ensure component compatibility and help reduce time spent in design, production, and assembly.
Interest among OEMs for fully integrated medical equipment systems has led to the design and development of subsystem medical tables. In one application example, these tables (one is mobile and the other is “fixed”) are incorporated into machines for urology. Through mechatronics components for multi-axis positioning, doctors can precisely, easily, and comfortably move patients for specific treatment.
Mechatronics has found a home in hospital rooms and in similar patient-care settings. Modular, power-driven actuation systems let caregivers precisely, safely, and securely adjust and position patient beds. Other applications include couches, stretchers, and physiotherapy and examination tables in various healthcare settings. Specialized actuators, recliners, and control units integrate
easily into standard bed platforms.
Beds equipped with such actuation systems can offer variable height adjustment; an adjustable backrest with CPR function; special positioning with auto-contour for comfortable sitting; and adjustable elevation of legs and knee-fold. Full electrical control comes from handsets, bilateral pedals, and selective function limiters. A manual quick-release mechanism safeguards in case of emergency.
Final Note: Regardless of application, an understanding of particular requirements and the operating environment will help guide your choices. Partnering early in the design stage with a knowledgeable engineering resource can help identify the best components or systems for the job.
Contact Mark D. Hinckley at 267-436-6510 or email Mark.D.Hinckley@SKF.com