Industrial encoders are used for various applications in the production industry. One type of industrial encoder is Incremental industrial encoders. These units, like incremental couplers, provide precise position measurement over an extended range.
Incremental industrial encoders are found in diverse industries such as power generation, printing, and packaging; automotive assembly, rubber, and plastic manufacture; metal fabrication, electronic assembly, and many more. The main function of industrial encoders is to monitor and measure one or more positions, using a device for observing and recording motion.
Incremental industrial encoders can be used in various applications, including accurate position measurement in machine tooling, testing, and inspection of parts, precise positioning of components during manufacture or assembly operations. Incremental digital industrial encoders are used for global positioning systems (GPS) as well as other applications.
Exact Position Measurement (APM), also called an incremental encoder, is a method used to provide accurate position measurements over an extended range by repeating the same measurement at predetermined intervals.
An incremental encoder is a device that can be configured to give an accurate measurement in less time than an AC or DC position sensor. The incremental encoder repeats the same measurement at a very short time interval. This is accomplished by producing an electrical pulse or signal (depending on the type of incremental industrial encoder) that is repeated at a much faster rate than what would normally be required if the same measurement was taken with a typical sensor.
The pulses of the pulse-rate signal are generated by an electronic circuit that generates a square wave of constant amplitude for each period of time; for example, one cycle per second produces four pulses per second (i.e., 500 cycles/second).
The time interval between pulses is defined by the pulse-period signal, which is generated by another electronic circuit that produces a square wave. The period of the pulse-period signal is usually constant, usually one millisecond. The division of the pulse period in time determines how long each pulse is produced.
The time interval between two consecutive pulses of the pulse-rate signal is a measure of how much displacement there has been since the last measurement. If a series of two pulses are taken at exactly 0.5 s intervals, it will appear as a single long “virtual” pulse; this indicates that the encoder has been displaced by half its range during these 0.5 seconds.
Incremental rotary encoder principle
The principle of measurement of an incremental encoder is based on two separate circuits that generate pulse signals of set periodicity. The time interval between pulses provided by the pulse-period circuit indicates the amount of movement of the axis.
The voltage generated across the terminals (usually X and Y) is used to drive a counter. The counter subtracts a given value from its stored value, which corresponds to initial displacement, and updates the stored value each time it receives a pulse signal from the pulse-period circuit. When it has counted all possible states, it outputs an analog signal indicating an angular position in degrees or radians.
The following figure shows how an incremental rotary encoder generates incremental pulses for motor control.
Incremental rotary encoder circuit
The following block diagram shows the analog signal path in a typical incremental rotary encoder. The analog signal from the X and Y lines of the incremental encoder is amplified (usually by an op-amp) and passed through a bandpass filter to remove noise created by internal circuits. The filtered signal is then passed through an integrator to give average current output proportional to displacement. This output is then fed into a comparator, which compares it with an adjustable reference voltage and generates a square wave pulse-rate signal at the TTL logic level as its output. This pulse-rate signal drives the external counter used for measuring angular displacement.
Analog signal path in an incremental rotary encoder
Incremental encoders are used in conjunction with other methods of position measurement to provide a local coordinate system with zero offsets. They are generally used to provide feedback signals for closed-loop systems (servo) where the position of an electric or hydraulic actuator is required. For example, they are used to control robot arms, robotic machine tools and pick-and-place machines, and automated assembly equipment.
To reduce the cost, size, and weight of the incremental encoder, an optical method is used to detect a change in light intensity generated by an internal rotating mechanism. This is then used as a signal to detect position.
The optical method also reduces the number of sensors needed, which is especially valuable for their use in mobile applications. This is because a sensor can not be installed near the rotating mechanism (for example, a turret) that is being measured. The following figure shows an optical encoder used in mobile applications.
Encoders by dimension
A rotary encoder is an optical, inductive, or magnetic device used to detect angular displacement. An encoder provides a digital output signal that is proportional to the angle of rotation. A sensor device (rotary encoder), which is mounted on a shaft or other moving part of a machine, detects and measures the angular displacement of the moving part and provides an output signal proportional to the measured displacement. The rotary encoder has two major applications for linear position measurement: As an absolute angular position sensor for machine tool servomotors, robots, and other motion control equipment; as an incremental signal generator for digital counting systems such as programmable logic controllers (PLCs).
Encoders for special requirements
A rotary encoder generates an electrical output as a function of the angular displacement or angle of rotation of its shaft. The electrical output is always proportional to the actual angle of rotation, ensuring that for any displacement, only one unique output is generated. This property makes rotary encoders suitable for use in closed-loop systems as angular position transducers, as well as systems requiring absolute position information. In such systems, one or more encoder signals are processed by a controller to produce a control signal that drives the motion (like an electric motor) to a specific setpoint.
A rotary encoder is a general name for something that is more specific. Therefore, some rotary encoders are used in the following applications:
The rotational speed of the wheel-mounted wheel-hub (“fine-particle wheel”) and a driven wheel of an electric motor must be accurately known. An encoder mounted inside the wheel hub detects the rotation speed and provides feedback to both wheels so they can be controlled by a servomotor or other closed-loop device. This configuration allows them to operate with very low slip, which improves fuel efficiency and reduces the wear on drivetrain components.
The encoder can also be used in applications where the probe position sensor is not in contact with the part to be measured. This is, for example, the case with shaft encoders. In such applications, the encoder may replace existing encoders on shafts that have similar accuracy requirements, or it may be used as a refinement to measure inaccuracies due to friction and wear. The latter case requires that the phase-to-phase difference between rotary shafts is known and controlled.
Conventional probes for position measurement usually consist of a flat conductive gage (similar to a steel pin) which does not offer much information about rapid variations in speed, just like an ordinary balance. In contrast, the encoder probes provide a rectangular signal (different phases between current and voltage) proportional to the position, which allows for precision positioning at high speed (especially for a round probe).
Servo systems are used to control motion in many applications. The motion can be of a mechanical nature, such as in robotics, machine tools, and system robotics. Servo systems may also be used for motion control of fluids or gases, as well as controlling electrical currents or voltages.
Baumer rotary encoders are used for many applications and are popular in machine building. They offer high tolerance and good performance at a low price, thanks to the solid integrated feedback system. The rotary encoders are optimized for multiple axis position measurement, implement a strong positioning function and provide excellent long-term stability due to the non-contact mounting with the shaft under test.
The Baumer encoder is ideally suited as a time-invariant positioning device in controlling spindles, screws, or cutting tools. Various forms of this type of position feedback system are used for precision machine control and motion measurement (e.g., programmable motor control).
A potentiometer is a three-terminal resistor with a sliding electrical contact that forms an adjustable voltage divider. A rotary encoder utilizes relative motion between a magnetic or optical target and a sensor to detect and encode its position. A resolver uses the phase-to-phase differences in two angular positions to calculate the angular displacement between them. Encoders are widely used in automotive applications like ABS, traction control, cruise control, automatic transmission and climate control systems.