Optical Encoders
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To introduce basic knowledge of optical encoders and OPTEK product portfolio
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Optical Encoders
- 4. Incremental / Absolute Encoders Indicates closed circuit, blank indicates open circuit Indicates closed circuit, blank indicates open circuit Incremental Encoder Absolute Encoder Quadrature 2-bit Code ¼ Cycle per Detent Code Position Output A B 1 2 ■ 3 ■ ■ 4 ■ 5 6 ■ 7 ■ ■ 8 ■ 9 10 ■ 11 ■ ■ 12 ■ 13 14 ■ 15 ■ ■ 16 ■ 4-bit Gray Code – 16 Position Code Position Output 1 2 4 8 1 2 ■ 3 ■ ■ 4 ■ 5 ■ ■ 6 ■ ■ ■ 7 ■ ■ 8 ■ 9 ■ ■ 10 ■ ■ ■ 11 ■ ■ ■ ■ 12 ■ ■ ■ 13 ■ ■ 14 ■ ■ ■ 15 ■ ■ 16 ■
Notas del editor
- This is a training module on Grayhill Inc. Optical Encoders
- Welcome to the training module on Grayhill optical encoders. This training module introduces how encoders work and their different applications, comparing different types of input solutions and an overview of different product families.
- The key components of an optical encoder are shown here. The shaft turns the code rotor. The LEDs emits infrared light. The photo detectors are special transistors that allow current to flow when the light from the LEDs is shining on them. The light from the LEDs is alternately blocked or allowed to pass to the photo detectors as the code rotor is turned. Two LED-photo detector pairs are used. These produce the outputs A and B as shown. The alternating on-off state produces the output signal.
- An incremental encoder is called “quadrature” because it repeats itself every four positions. The alternating on-off state produces the output signal. A microprocessor chip that reads a quadrature encoder can only determine the direction, clockwise or counterclockwise, and the amount of increments, number of detent positions, that the encoder shaft has been rotated. A microprocessor cannot determine the absolute rotational position of the shaft. In some cases, the customer’s application will require the encoder output a unique, non- repeating, code for each incremental position the shaft is rotated. An incremental encoder will not work in this kind of application. The application requires an absolute encoder. The table shows how 16 unique output codes are created.
- Specific encoders can be specified in terms of the pulses per revolution or PPRs of the output signal. This is the number of quadrature state changes per 360° rotation of the code rotor. Encoders can alternately be specified in terms of their cycles per revolution or CPRs. This is the number of full quadrature cycles per 360° rotation of the code rotor. Please note that there are four pulses in every cycle.
- Common characteristics of Grayhill optical encoders are: Very high life ratings, typically 1 million to 300 million cycles - this is because they do not use mechanical contacts that tend to wear out over time. They are active devices that require a power source - this is typically 5V but Grayhill can customize the operating voltage if required. The majority are available with standard connector and cable options . Customizations include shaft and bushing configurations, special detent or rotational feelings, customer specified terminations and special output codes .
- The features of human interface encoders are: They are low resolution - their resolution is specified in pulses per revolution They have detents - these allow the operator to feel when the shaft clicks into position as the shaft is rotated They also have a pushbutton feature that is used to enter or choose menu selections
- Grayhill offers four general purpose optical encoders suitable for human interface applications. The first encoder was the 61B. Grayhill developed the 61C, 62A and 62S products in order to satisfy evolving customer requirements for lower cost and smaller package sizes. The 62S is the latest offering which is our smallest package size encoder.
- Grayhill human interface encoders are used in many industries. For instance, they are used in medical devices such as ultrasound equipment, patient monitoring devices, defibrillators, and x-ray equipment. They are also used by the automotive industry in dashboard and console navigation systems and climate controls. Industrial applications include machine tools, process controls and factory automation. Encoders can also be found in lab instruments, avionics, communication equipment and handheld tablets.
- This page gives you advantages of human interface encoders. For any application, the customer has a variety of input devices to choose from. It is important to understand how optical encoders compare to other types of input solutions. An encoder can be mounted on the front panel of the device. This results in a self contained assembly that does not require additional space or surfaces for a mouse pad.
- Grayhill offers four general purpose optical encoders suitable for human interface applications. 61B series product is first optical encoder. On customer demand, Grayhill subsequently developed products the 61C, 62A and 62S which are lower cost and smaller package sizes. The 62S is the latest offering. It is our smallest package size encoder. In addition, it is available with many standard catalog options as shown in the table.
- Grayhill has also developed several encoders with special features for various applications. The 60A and 60C joystick encoders incorporate an 8-way mechanical joystick. This allows the customer to incorporate additional functionality into their product without using additional panel space. The 60C separates the pushbutton and joystick from the encoder on concentric shafts. Applications for these products include automotive climate controls and rear seat entertainment systems, avionic information management systems and oven temperature and humidity controls. The Grayhill 62C is a concentric shaft encoder with a non-rotating inside shaft. This is required when the customer wants the pushbutton feature to be on a different shaft to prevent accidental actuation. The non turn shaft also insures that any legends printed on the knob stay in their proper orientation. Applications for these products include avionics and medical devices.
- Grayhill offers a family of products with high torque detent systems. These products require two to four times more rotational force to actuate compared to standard encoders. They are used by customers that desire an additional degree of security and tactile feedback. Typical applications include avionics or any application where the device is used by an operator wearing gloves. The 62B encoder has a pull-to-actuate feature in its shaft in addition to the typical pushbutton feature. The pull-to-actuate shaft is almost impossible to actuate accidentally. A customer can use this product to incorporate “push-for-off , pull-for-on” OR “push-to-enter, pull-to-reset” functionality into their equipment. This product is targeted to the avionics industry.
- The 62V encoder operates at a lower voltage of 3.3V than standard encoders that operate at 5V. It consumes less power which makes it ideal for battery powered devices. The lower voltage also reduces risk in explosive environments. The 62F is an optical encoder with an LED and light pipe incorporated into the shaft. The 62F simplifies the customer’s design when the knob is required to be illuminated. The customer does not have to worry about incorporating the lighting circuitry into their panel. The 62R is an optical encoder with a second set of backup circuitry. The encoder will still function in the unlikely case of a failure of the primary circuit. Originally designed for a helicopter ground avoidance system, this product is designed for ultra critical applications like avionics. The 62P was introduced as a low cost optical encoder to compete against printed circuit board mounted mechanical encoders. It has the advantage of high life, 500,000 cycles, and it does not require extra “debounce” circuitry .
- Grayhill offers three higher resolution encoders suitable for human interface applications. These products are used where fine adjustment, greater accuracy and a smooth, continuous rotational feel is required. The original 61H and 61J products can be produced with resolutions up to 128 cycles per revolution. This is equivalent to 512 pulses per revolution. Previously a maximum of 32 pulses per revolution were available. On market demand, 256 cycle per revolution products 61K and 61R encoders were developed. Grayhill uses a special chip instead of photo detectors in 61S product in order to achieve the reduced package size. Applications for these products include electric welding machines, medical ventilators, test equipment, audio mixing consoles and high-end audio amplifiers.
- Applications for higher resolution products include electric welding machines, medical ventilators, test equipment, audio mixing consoles and high-end audio amplifiers.
- In a machine interface application, the encoder is used as a feedback device in a motion control system. This means that the encoder is installed with moving equipment and is not turned by hand. It has higher resolution and are specified in cycles per revolution, not pulses per revolution. They do not have detents or pushbutton features. They may be built with ball bearings to withstand high shaft RPMs and high shaft loads. Typical machine interface applications include motor shafts, conveyor belts, machine tools, robots, factory automation, office printer/copier mechanisms, antennas and telescopes, elevators, printing equipment and smartcard fabricating equipment. Other machine interface applications require encoders that can withstand high shaft speeds and some level of shaft loading. Grayhill produced the 63K and 63R ball bearing encoders for these applications. Applications for the 63K and 63R include propane gas flowmeters, bulk processing flowmeters, fluid flowmeters, automated vial samplers and lift trucks.
- In order to further penetrate the machine interface market, Grayhill now offers the following high-resolution products: The 63A is a 256 CPR absolute encode because this absolute encoder outputs 256 unique codes per each 360 degree rotation. It is suitable for applications where the absolute position of the encoder must be known when the device is powered-up. The 63Q is a 1024 CPR incremental encoder. The 63T is a hollow shaft version of the 63Q suitable for mounting on a motor or other shafts in a motion control system. These products are used in applications such as motor shafts, conveyor belts, machine tools, robots, factory automation, office printer/copier mechanisms, antennas and telescopes, elevators, printing equipment and smartcard fabricating equipment.
- Applications for the 63K and 63R include propane gas flowmeters, bulk processing flowmeters, fluid flowmeters, automated vial samplers and lift trucks . These products are used in applications such as motor shafts, conveyor belts, machine tools, robots, factory automation, office printer / copier mechanisms, antennas and telescopes, elevators, printing equipment and smartcard fabricating equipment .
- Thank you for taking the time to view this presentation on “Optical Encoder ” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link, or simply call our sales hotline. For more technical information you may either visit the “Grayhill” site, or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility. You may visit Element 14 e-community to post your questions.