Trio Motion Technology



	Armature:
	The rotating part of an electric motor. In a conventional DC brushed motor the armature supports the coils which carry the electric current.


	Back EMF:
	The electromotive force (voltage) produced by a motor acting as generator. Back EMF is generated at all times by a motor although it will be smaller than the voltage being used to drive current though a motor when running at constant speed.


	Backlash:
	The motion required to take up the mechanical tolerances or wear after change of direction in a machine part such as a gearbox.


	Brushless Motors:
	Motors in which commutation is performed using electronic switches rather than using mechanical brushes. In most DC Brushless Motors the armature supports permanent magnets and the motor coils are arranged mounted surrounding the armature. This configuration reverses that of a conventional DC brushed motor.


	Commutation:
	The process whereby current is fed to the different coils of a motor to try to maintain constant torque as the motor rotates. In a brushed DC motor the brushes act as on/off commutation switches. In a brushless motor the servo drive gradually varies the current into each phase of the motor.


	Encoder:
	Usually refers to an Incremental Optical Encoder. An encoder may be mounted on a motor or machine part to indicate it’s position to a control system. An incremental optical encoder consists of a disk with a few hundred or thousand slots, and 2 optical sensors which produce an out of phase pair of signals referred to as A and B channels. A third optical sensor, produces a once per turn signal, referred to as the Z, or 0, channel. Incremental Optical Encoders provide a control system with incremental position changes


	Electronic Commutation:
	Commutation in a brushless motor system. The servo drive switches current into the motor windings depending on the relative position of the rotor and the motor windings.


	EnDat™:
	A format devised by Heidenhain for serially transmitting information from an absolute encoder into a control system. RS485 signals are used to transmit the absolute encoder position (including possibly multi-turn data) at high speed into the control system. EnDat is the trademark of Heidenhain.


	Feedback:
	The provision of measured information from a system under control to allow a servo loop to be constructed. A servo motion control system typically will have current, speed and position feedback.


	Gray Code:
	A format for encoding numbers used instead of binary in absolute encoders. Gray codes allow only one bit of the pattern to change at a time when counting up or down. For example, when changing from 15 to 16 in binary bits 0,1,2 and 3 will all change simultaneously.


	Hall Sensors:
	A simple low cost way of providing a brushless motor’s approximate absolute position to a servo drive. Hall sensors are often used to allow for simple trapezoidal commutation.


	Hiperface:
	A format devised by Stegmann for serially transmitting information from an absolute encoder into a control system. RS485 signals are used to transmit the absolute encoder position (including possibly multi-turn data) into the control system. Hiperface is the trademark of Max Stegmann GmbH.


	Inertia:
	The resistance of a body to accelerate when a force is applied due to its mass.


	Linear Motors:
	Different configurations of linear motors are available which correspond with brushed, brushless servo or stepper motors. In many cases they can be considered as a rotary motor which has been rolled out flat. In a brushless motor typically permanent or electro magnets are arranged in a row and the electric windings are arranged on a moving carriage.


	Load Inertia Ratio:
	The ratio between the rotary inertia of the load as seen by an electric motor and the motors own inherent rotary inertia. As this ratio increases the load will become harder for the motor to control and the frequency response will become lower. A key factor in machinery design for servo systems is selecting the transmission ratio (using gearboxes and toothed belts) to achive a suitable balance between the Inertia Ratio and the motor speeds.


	Microstepping:
	A technique for sub-dividing steps on a stepper motor. Microstepping allows a stepping motor to stop and hold a position between the step positions, and reduces the jerk between steps giving less noise and resonance.


	Optical Encoder:
	See encoder.


	Phase:
	Many brushless motors are 3 phase. There are 3 coils within the motor which are each fed with a current depending on the position of the rotor. The relative current in each phase of the motor is calculated by the drive to produce the torque in the motor as it rotates.


	PWM:
	Pulse Width Modulation is the technique where current is fed into motor phases as a sequence of rapid on/off cycles using electronic switches such as transistors or IGBT’s at typically 20-50kHz. The short pulses are smoothed by the inductance of the motor windings.


	Resolver:
	A single turn absolute position feedback device frequently built into servo motors. The absolute nature of a resolver allows it to be used for electronic commutation. A resolver is a rugged inductive device that may be considered as signal transformer with a primary and 2 secondary coils. An excitation sin wave is fed into the primary and the rotary position of the transformer is indicated by the relative magnitude of the 2 secondary sin wave outputs.


	Rotary Inertia:
	The resistance of a rotating object to angular accelerate when a torque is applied.


	Servo:
	A servo system is a closed loop control system. It incorporates a demand requirement of a parameter such as position, feedback of the measured parameter, and a method to close the difference. A servo motion control system typically will have current, speed and position feedback servo loops.


	Sinusoidal Commutation:
	In an idealised system for controlling 3 phase motors the current in each phase will be varied in a sin wave profile as the motor rotates. Servo drives with accurate feedback of the motor position are able to modify the motor phase currents in this way using sinusoidal commutation. Sinusoidal commutation is typically performed in motors fitted with resolvers or absolute encoders.


	SINCOS Encoder:
	A type of optical encoder where the output signals are 2 analogue channels, out of phase by 90 deg. Electronic circuits can interpolate the analogue signals to give high position resolutions. A SINCOS encoder might have 4096 analogue pulses/turn. Each analogue pulse might be interpolated to 1024 sub-divisions giving a resolution of approximately 4 million counts/turn.


	SSI:
	A format for serially transmitting information from an absolute encoder into a control system. RS485/422 signals are used to transmit the absolute encoder position (including possibly multi-turn data) at high speed into the control system in either binary or gray code format.


	Stepper Motor:
	A type of electric motor typically used in lower cost applications. Current is applied to the motor phase windings either in steps or using “microstepping”, similar to sinusoidal commutation, to rotate a permanent magnet rotor synchronously. A stepper motor will maintain it’s position provided the torque and speed required by the application are well within the motor’s limits.


	Torque:
	Turning, or rotational, force.


	Torque Constant Kt:
	How much torque a motor will produce per ampere of current supplied . One of the key parameters for a servo motor. The units are Newton Metres/Amp.


	Trapeziodal Commutation:
	A simple form of electronic commutation used where a brushless motor’s absolute position is returned by 3 on/off sensors built into the motor. This results in greater torque ripple in the motor output.


	Trap Drive:
	A low cost drive using trapezoidal commutation.


	Voltage Constant Ke:
	How much rotary speed a motor will produce for the voltage supplied . One of the key parameters for a servo motor.