Linear Motors
------------------------------------------------------------------------------

1、Description of Linear Motors

The same electromagnetic force that produces torque in a rotary motor and also produces direct drive force in a linear motor or actuator. For example, a permanent Magnet DC linear motor is similar to a permanent magnet DC rotary motor and an AC induction linear motor is similar to a squirrel cage induction motor. Take a rotary motor, just split it radially along its axis of rotation and flatten it out. The result is a flat linear motor that produces direct linear drive force instead of rotary torque. It follows that linear motors utilize the same controls as same as rotary motors.  And similar to a rotary motor with rotary encoders, linear motor positioning is provided by a linear encoder. Typical linear motors are referred to as positioning platforms or actuators.

2、Advantages and Features of Linear Motor System

2-1   Unlimited Travel
Non-limitations on travel displacement
2-2   Wide Velocity Range
It can be applied to both very low and very high velocity requirements and all with very high precision. They can precisely run in quite big velocities range.
2-3   Fast Acceleration and Response
Linear motors are capable of very high acceleration and settling times.
2-4   Excellent Accuracy and Repeatability
Linear Motors with Excellent positioning accuracy and Repeatability, use as an essential component or element for achieving very high positioning accuracy.
2-5   Stiffness
Regarding no mechanical linkage or rigid contact, increasing the stiffness is Simply a matter of gain and current. The spring rate of a linear motor driven system can be many times compared with that of a ballscrew driven devices. However it must be noted that this is limited by the motors peak force, the current available and the resolution of the feedback.
2-6   Zero Backlash
Without mechanical transmission components and elements, there is no backlash. Resolution considerations do exist. That is the linear motor must be displaced by one feedback count before it will begin to correct its position.
2-7   Maintenance and Life
Considering no mechanical contact design and no friction between two working Contracting parts, Life is an extremely long, virtually maintenance-free life.
2-8   Cleanroom and Vacuum Applications
The coils parts and the magnets parts of linear motors do make non-contact, This mean the contracting parts no wear or no friction. They are ideally fitted for cleanroom and vacuum surrounding applications.
2-9   Noise down
The elimination of sliding surfaces, rolling and recirculating elements reduces many sources of noises, Thus Linear motors may run very quietly.

3、Typical Linear Motor Systems

Toptech linear motors: Flat Type Linear Motor and U-Type Linear Motor
3-1   Cogging-Free Brushless Linear Motor:   LMCF
3-2   Iron Core Brushless Linear Motor:      LMIC
3-3   Ironless Brushless Linear Motor:       LMBL

4、Linear Motor Typical Applications  

Baggages Handling and Mails Sorting
Labeling, Printing and Packaging Machines
Food Processing and Automatical lines
Laser Cutting Machines
MRI & X-Ray Equipments
Semiconductor, PCB Manufacturing and Assembly lines or Inspection
Precision Grinding
Robots or CNC Machines and Cars Lines  Etc.

5 、Useful Linear Motor Definitions or Glossary
5-1   Continuous Force (FcTmax)
The force produced by continuous current (IcTmax), all the phases sharing the load,  provided the coil is secured through an adequate thermal heatsink as specified. This scenario produces a coil temperature equal to the Tmax rating for the motor.
5-2   Peak Force (Fp)
The force produced by peak current (Ip). Ip assumes a 4% duty cycle with a maximum on time of one second.
5-3   Motor Constant (Km)
This is a figure of merit for motor efficiency. It is the ratio of the continuous force (three phases) FcTmax to the square root of the motor power losses in the three phases.
5-4   Thermal Resistance (R th)
The equivalent thermal resistance of the motor, determined by the ratio of coil temperature rise to the total power motor losses in the three phases. We assume the motor is mounted on a heat sink of at least the size specified in this catalog, with ambient temperature below 20°C and with a stroke of at least twice the coil length.
5-5   Max Power Dissipation (PcTmax)
The continuous power losses of the motor when the RMS current in the coil is IcTmax and the ambient temperature below 20°C.
5-6   Maximum Applied Bus Voltage (VDC)
This is the maximum allowable Bus DC voltage that can be applied to the coils.
5-7   Electrical Cycle Length (Ec)
This is the length of the electrical cycle and corresponds to twice the magnet length (North to North).
5-8   Electrical Time Constant (ôe)
The time it takes for a step current input to the coil to reach 63% of its final value by overcoming the resistance and the          inductance of the coils.
5-9   Maximum Coil Temperature (Tmax)
The maximum rated service temperature of the coil = 130°C. However,  good practice is to limit the RMS current to no more than 80% of the rated continuous current (IcTmax).
5-10  Magnetic Track Mass (Mm)
The mass of the magnetic track per unit of length.
5-11  Force Constant (Kf)
The ratio between the motor continuous force (FcTmax) to the motor continuous Current (IcTmax). For these motors, the force constant does not change as a function of current.
5-12  BEMF Constant p-p (Ke)
The ratio between the back emf voltage in volt peak to the motor speed.
5-13  Peak Current (Ip)
The magnitude of the three-phase sinusoidal currents that need to be applied to the motor to develop the motor peak force (Fp).
5-14  Continuous Current (IcTmax)
The continuous current corresponding to the continuous Force. This is a sinusoidal current which can be expressed either in Amp 0-peak or in Amp rms.
5-15   Resistance p-p @ 20°C (R20)
This is the cold coil resistance measured phase to phase (line to line) at 20°C.
5-16   Inductance p-p (L)
This is the coil inductance measured phase to phase (line to line).
5-17   Magnetic Attraction (Fa)
The magnetic attraction force exerted between the coil assembly and its magnet  assembly, measured at the nominal air gap.
5-18   Coil Mass (Mc)
The mass of the coil including the standard cable length.
5-19   Abbe Error
The angular error that occurs when the measuring point of interest is displaced from the actual measuring scale location.
5-20   Acceleration
Rate of change of velocity in g’s (Gravity constant) which is equal to 386in/sec2 = 9.81 m/sec2.
5-21   Accuracy
Measure of discrepancy between the expected and the actual position. Accuracy is indicated as the maximum deviation from the target location.
5-22   Backlash
Deadband (lost motion) caused by clearances between mechanical motion components Which may occur when starting or reversing direction.
5-23   Bandwidth
Frequency range in which a servo operates.
5-24   Cogging
The tendency of some linear motors to move unplanned discrete distances. This effect is a result of varying magnetic forces along the length of the motor and platen.
5-25   Commutation
The sequence at which the controller switches the drive voltage/current among the various motor windings to ensure smooth linear motion of the motor. Commutation can be achieved through the use of brushes, Hall Effect sensors,or with a sinusoidal current.
5-26   Duty Cycle
Percentage of time during a specified time interval that power is applied to the motor. If time on is greater than 30 seconds the duty cycle is 100%.
5-27   Electric Time Constant
Time in seconds for a step current input to reach 63% of its final value.
5-28   Force Ripple
The periodic force variation that occurs when the motor is in operation.
5-29   Full Step
Longest distance that a stepper motor moves during one pulse.
5-30   Hall Effect Sensor (HES)
A semiconductor chip that senses magnetic flux changes when passing over magnets. Typically, a Hall Effect Sensor is used for commutation in brushless motors.
5-31   Home Position
Unique position used as the initialization location from which all other programmable locations are referenced. Also known as the reference marker.
5-32   Laser Interferometer
Feedback device used to measure the distance between the incident and reflected light beam. Provides the highest degree of resolution and accuracy.
5-33   Mapping
Method used to calibrate or compensate for repeatable system errors.
5-34   Orthogonality
Measure of squareness (90 degree relationship) between motion axes. The value of error is typically expressed in arc-seconds.
5-35   Platen
The long stationary component of the linear motor.
5-36   Primary
The linear motor component that contains the coil assembly.
5-37   Resolution
The smallest displacement that a motor is able to move or the smallest displacement an encoder is able to detect.
5-38   Settling Time
Time required for the system to settle within a finite error band of its final position after a commanded move.
5-39   Velocity Ripple
Periodic velocity fluctuation that occurs when the motor is in operation.

6    Useful  Motor Unit Conversion

6-1    Rotary Inertia
6-2    Torque
6-3    Materials Densities    
6-4    Friction Coefficients
6-5    Mechanism Efficiencies
6-6    Temperature
6-7    Gravity
6-8    Length (L)
6-9    Power (P)
6-10   Mass (WT)
6-11   Force (F)
6-11   Linear Velocity (V)

7      Linear Motor Order needed Information

E-mail:   hktoptech@toptechelectric.com
Website:  www.toptechelectric.com