What is an Encoder?
Simply put, an encoder is a communication device that controls the motion of an operating device.
What are encoders used for? Encoders can help determine the speed or position of a motor, or other moving equipment.
As automation in many industries and applications spreads rapidly, encoders help to maintain speed and position in electromechanical equipment, a vital process when accuracy, repeatability and precise motion is necessary.
Encoders are used widely throughout many applications, including automotive, laboratory and medical equipment, robotics, factory automation and electric motors.
Traditionally, optical encoders were used most widely in motion control, but as the need for a more robust, rugged sensing solution increased, magnetic encoding technology has started to surpass optical encoders as a better solution for difficult environments.
Benefits of encoders in modern technology
The expanding integration of automation across diverse industries has heightened the demand for reliable servo systems capable of tackling a fresh array of operational hurdles.
Today, automation finds its footing in realms like packaging, paper handling, power generation, and other environments characterized by dirt, heat, humidity, and significant vibration levels. Optical encoders, initially designed for cleaner automation environments, have been adapted for more rugged applications with some degree of success. This has resulted in the development of high-cost, devices such as resolvers or sealed optical encoders. However, recent strides in magnetic sensor technology have ushered in magnetic encoders as a more feasible alternative for machinery operating in environments marked by heightened shock, vibration, and contamination levels.
What are optical encoders?
Optical encoders rely on line-of-sight sensing mechanisms to generate signals.
This involves a light source splitting into two 90-degree out-of-phase beams, traversing transparent, evenly-spaced windows within a rotating optical disc. A receiver captures and converts the light into digital square wave quadrature output signals. However, the efficacy of these signals hinges on a clear, consistent line of sight. Any material interference obstructing the light source can lead to signal disruption and encoder failure, particularly in servo systems operating in dusty and humid environments where particles can infiltrate the optical path. Moreover, fluctuations in humidity and temperature may prompt condensation formation on the rotating disc, further jeopardizing operational integrity.
Maintaining an optimal air gap between the pulse disc and optical sensor is crucial for reliable operation. Typically, this gap measures less than 0.25 mm (0.010”), necessitating utmost precision to preserve light signal integrity and accuracy. Consequently, optical encoders remain vulnerable to shock and vibration, potentially resulting in damage to the rotating optical disc or sensor. While traditional solutions involve sealed, ruggedized packaging to enhance resilience against vibration, shock, and temperature variations, these enhancements often translate to bulkier and costlier products.
Resolvers offer a sturdy alternative to optical encoder technology
Typically, brushless resolvers comprise two static windings offset by 90° mechanically, along with a rotary or reference winding receiving sinusoidal current from a rotary transformer.
As rotation occurs, induced currents in each static winding are gauged, providing position information based on their relative signal intensities. The robustness of this device stems from its construction materials and signal production method. While resolvers exhibit near-immunity to environmental hazards prevalent in industrial settings, their control systems generally entail higher costs compared to optical or magnetic encoders. They necessitate a resolver to digital (R to D) converter integrated circuit positioned remotely, thus mandating cabling for transmitting low-level signals. This wiring complexity can augment challenges related to installation, operation, and maintenance.
Progress in magnetic encoding technology has led to the creation of compact, economical encoders better suited for harsh, contaminated operating conditions, where optical encoders might encounter pulse skipping.
At Timken, engineers have patented novel magnetic encoder designs leveraging Hall effect technology to achieve high resolution from a resilient magnetic target disc. Magnetic sensing obviates the necessity for a clean transparent gap; only a certain distance between the magnetic target and sensor is required for proper operation. As long as this gap remains free of ferrous materials, magnetic pulses are detected by MPS technology. Contaminants such as dirt, dust, oil, and condensation do not compromise the reliability of magnetic encoders. Magnetic encoders also have the ability to better withstand the effects of shock and vibration. The gap between the sensor and target magnet surpasses that of an optical encoder, reaching up to 4 mm (0.157”) without sacrificing signal accuracy. These encoders accommodate end play and run-out tolerances as high as 2.5 mm (0.98”) total, minimizing the risk of target disc and sensor impact damage. Magnetic sensing technology obviates the need for ruggedizing magnetic encoder packages. With substantial gap requirements, immunity to light-impeding contaminants, and construction materials rated up to 135°C (275°F), modular packaged encoders can be utilized without incurring additional costs. Moreover, digital quadrature output signals mirror those of optical encoders, bypassing the supplementary control expenses typically associated with resolvers.
We offer two different types of magnetic encoder
There is the complete package option and the single-sensor chip option.
The M15 modular magnetic encoder is a high resolution speed and position feedback sensor for use in mechanical systems which require shaft position or speed feedback. The M15 encoder has been designed so that it can be integrated using common mounting and connection formats used in automation.
It is particularly suitable for both brushless and brush-type servomotors as well as smart stepper motors. This encoder can replace optical encoders in existing motor designs, offering mechanical and electronic signal compatibility. Shared features with optical encoders include commutation, index pulse, and options for open collector or line driver outputs.
Commutation signals in the M15 are generated by three small, independent Hall effect sensors located on the encoder PCB. These sensors detect a secondary magnetic track on the target magnet, separate from the MPS160 sensor magnet track, and positioned inboard of it. The digital Hall effect sensors switch high when detecting a north pole and low when detecting a south pole. The arrangement of pole pairs on the magnet commutation track and the placement of the three sensors produce three commutation signals—U, V, W—phased at 120 electrical degrees.
Case studies highlighting the successful use of magnetic encoder technology
Timken's magnetic encoder technology, available in both the M15 encoder's packaged format and the MPS Encoder ASIC's single-chip format, has enabled customers across various industries to enhance their application performance.
This advanced technology has been effectively implemented in automotive steering systems, stepper motor drives, mining trucks, measurement systems, medical devices, lighting systems, and transmission sensors for off-road equipment. Below are case studies highlighting the successful use of magnetic encoder technology in two specific applications.
Stepper Motor Drives:The Timken M15 encoder has proven to be highly effective in stepper motor drives used in automated lighting systems for indoor and outdoor stage productions.
These drives control the horizontal movement, tilt, and rotation of stage lights. In one instance, the M15 encoder replaced a similarly sized optical encoder, delivering superior performance. The M15's design facilitated integration into existing beta units for testing, where it was securely mounted within the customer's stepper motors. Both laboratory and field tests demonstrated that the M15 encoder was less susceptible to debris, condensation, adverse weather, and extreme temperatures compared to optical encoders. As a result, the M15 encoder is now used in production units.
Schneider MDrive® Actuators: In another industry, a customer enhanced the precision and reliability of its motion control systems by using the MPS Encoder ASIC linear encoder ASIC.
Schneider Electric Motion USA (formerly IMS Motion Control Systems), a global leader in all-in-one motion systems for robotics, pharmaceutical processing, and the manufacturing of medical, biomedical, electronic, and semiconductor products, replaced optical encoders in its Schneider MDrive® actuators with the MPS Encoder ASIC. These actuators enable automated equipment to achieve high accuracy and repeatability in movement. The MPS Encoder ASIC provides feedback on the shaft's position and speed, allowing for an off-axis design and installation in compact spaces. Previously, Schneider's stepper motors relied on remote drives with external optical encoders connected by cables, which caused noise and debris contamination issues. The MPS Encoder ASIC overcame these challenges by being integrated directly into the motor's embedded electronics.
Schneider also selected the MPS Encoder ASIC for its programmability, which simplifies product customization. The company can quickly program the sensors for the required number of pulses per revolution, install the encoders in the MDrive® units, and dispatch them for installation in automation equipment.
Magnetic encoders offer several benefits over traditional optical encoder designs, including enhanced durability, reliability, and a more compact form factor.
They are particularly well-suited for use in harsh environments with dirt, humidity, high temperatures, and significant vibration. Utilizing Hall effect technology, magnetic encoders have demonstrated successful operation in various demanding applications. These include stepper motor drives in automated stage lighting systems and the Schneider MDrive® actuators, which are integral to a range of industrial automation systems. This next generation of off-axis magnetic sensor technology has been effectively applied in automotive steering systems, mining trucks, measurement systems, medical devices, lighting systems, and transmission sensors for off-road equipment.
When choosing the appropriate encoder technology for a specific application, engineers should evaluate environmental conditions, packaging constraints, resolution requirements, and cost considerations. Magnetic encoder technology is particularly advantageous in scenarios where performance cannot be compromised, and the operating environment is challenging. It offers a reliable and cost-effective solution to meet these stringent demands.