Stepper & DC Servo Motors… A Brief Tutorial

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Stepper & DC Servo Motors… A Brief Tutorial Powered By Docstoc
					                         Motion Control
Translation Stages       apt™ Modular Stepper Motor Driver
Motorized
Mirror Mounts         The apt™ modular rack system is a sophisticated, self-contained, extendible
                      architecture, precision motion control platform for high channel count motion
Rotation Stages       control applications (see page 352 for details of the rack enclosure). Our modular
3 Axis Flexure Stages apt™ stepper motor driver provides a scalable motion control solution which
& Accessories         allows the independent control of up to 12 stepper motors within a single 19" rack
                      enclosure. The USB interface and advanced application software, allow multiple                    MST601
4, 5 & 6-Axis Stages
                      channel systems to be seamlessly integrated into a single large scale solution.
Drive Electronics     Additionally, it is possible to combine the apt™ rack systems with one or more bench
& Auto-Alignment                                                                                                        For simplicity of operation, the apt™ software
                      top apt™ units. The plug-in modules have all the same performance and ease of use
Actuators &                                                                                                             incorporates pre-configured settings for each of
                      features as our bench top drivers presented on pages 334 through 337. They combine
Adjusters                                                                                                               the Thorlabs’ stages and actuators, while
                      the latest high-speed digital signal processors (DSP), low-noise analog electronics, and
                                                                                                                        highlighting and making available all operating
                      ActiveX® software technology. The modular apt™ stepper motor controller is supplied
                                                                                                                        parameters for use with other manufacturer's
                                                        ■
                                                                                                                        stepper motor systems. For convenience and ease
   Features                                                   User Controlled Digital I/O Port
                                                                                                                        of use, adjustment of many key operating
  ■    Dual (Synchronised) Drive Channels               ■     Motor Control I/O Port
                                                        ■
                                                                                                                        parameters is also accessible through the software
  ■    Supports 2 Phase Bipolar Steppers up to 50W            Full Software GUI Control Suite
                                                        ■
                                                                                                                        generated control panels. Furthermore, move and
  ■    Differential Encoder Feedback (QEP inputs)             ActiveX® Graphical Panel Controls
                                                                                                                        jog commands can be performed directly from
  ■    Maximum 128 Microsteps per Full Step             ■     ActiveX® Programming Interfaces
                                                                                                                        the GUI panels. All settings and parameters are
   ■   25,600 Microsteps per Rev (200 Step Motor)       ■     Seamless Software Integration with apt™ Family
                                                                                                                        also accessible through the ActiveX®
                                                                                                                        programmable interfaces for automated
                                                                                                                        alignment sequences. See pages 354-356 for
                                                            with a full suite of software support tools. An intuitive
                                                                                                                        a full description of the apt™ system software.
                                                            graphical instrument panel allows immediate control
                                                            and visualization of the operation of the stepper           Full Support for Encoder Feedback
                                                            controllers, and any other plug-ins that are installed in   The modular apt™ stepper motor controller also
                                                            the system. See pages 354-356 for a full description of     supports encoder feedback through dedicated
                                                            the apt™ system software.                                   quadrature encoded pulse (QEP) inputs, one for
                                                                                                                        each channel of the two channels of operation.
                                                      Driver Functionality
                                                                                                                        Through conversion routines, the apt™ software is
                                                      A wide range of 2-phase bipolar stepper motors and
                                                                                                                        able to use this feedback signal to generate encoder
                                                      associated actuators are commercially available, each
                                                                                                                        position for access either through the GUI or via
                                                      with its own characteristics, such as step resolution,
See pages 354-356                                                                                                       programmable interfaces for use in custom closed
                     peak phase current or voltage, and lead screw pitch. Operation of the apt™ stepper
for more information motor controller is fully configurable (parameterized) and all of the key settings are             loop algorithms. A “built in” algorithm can be
on the apt™ software accessible through a number of graphical interface panels. For example, the motor step             enabled to allow the stepper system to reach and
included with the                                                                                                       maintain an encoded position through an iterative
                     resolution and lead screw pitch can be set for a particular motor/actuator combination,
MST Controller.                                                                                                         move sequence.
                     phase currents can be limited to suitable peak powers as required, and limit switch
                     configuration is accommodated through a flexible set of limit switch logic settings.
                     Moreover, relative and absolute moves can be initiated with move profiles set using
                     velocity profile parameters. Similarly, home sequences have a full set of associated
                     parameters that can be adjusted for a particular stage or actuator.


   Stepper Controller Specifications                    ■     Stepping (Assumes 200 Step Motor)
   ■   Input/Output:                                            – 25,600 Microsteps per Revolution
       • Motor Drive Channel                                    – Maximum 128 Microsteps per Full Step                       Rack System
         (25 Pin D-type Female)                         ■     Compatible Motors:                                             See Page 352
         – 2 Phase Bipolar Motor Drive Output                 • Peak Powers: 5 to 50W
         – Differential Quadrature Encoder Interface          • Average Power: 25 W Maximum
         – Forward, Reverse Limit Switch Inputs               • Step Angle Range: 20° to 1.8°                                            MOTOR DRIVE
       • Motor Control (15 Pin D-type Female)                 • Coil Resistance (nominal): 4 to 15Ω
         – Jog Forward                                        • Coil Inductance (nominal): 4 to 15mH
         – Jog Back                                           • Rated Phase Currents (nominal):
         – Enable/Disable Interlock                             100mA to 1A
         – Jog Control Handset Available                ■     General:
       • User I/O (26 Pin D-type Female)                      • One Slot apt™ Rack
         – RS 485 Communications Channels                     • Dimensions (W x D x H):
         – Logic Level Trigger Input/Output                     190 x 270 x 50mm
                                                              • Weight: 1.5kg (3.3 lbs)


                          ITEM#                    $                  £               €                 ¥                                DESCRIPTION
                          MST601               $ 1,358.30        £   799.00      € 1.198,50        ¥   223,720            apt™ 2 Channel Stepper Motor Controller Module


338                      Sales: 973-579-7227
                                                                                                                                     Motion Control
Stepper & DC Servo Motors… A Brief Tutorial                                                                                                                               Translation Stages

                                                                                                                                                                                   Motorized
Thorlabs offers a range of benchtop and rack mounted motor                        How a Brushed DC Motor Works                                                Mirror Mounts
controllers covering both low and high power applications. These                  A DC motor works by converting electric power into mechanical
are described on page 331 to 338. The following two pages contain                 energy (movement). This is achieved by forcing current through a           Rotation Stages
a brief tutorial on how stepper motors and DC motors operate,                     coil and producing a magnetic field, which in turn, spins the motor. 3 Axis Flexure Stages
together with a comparison of the two types.                                                                                                                                   & Accessories
                                   How A Stepper Motor Works                                                                                                             4, 5 & 6-Axis Stages
                                   Stepper motors operate using the principle
                                                                                                                                                                           Drive Electronics
                                   of magnetic attraction and repulsion to                                                                                                 & Auto-Alignment
                                   convert digital pulses into mechanical shaft                                                                                                 Actuators &
                                   rotation. The amount of rotation achieved                                                                                                       Adjusters
                                   is directly proportional to the number of
                                   input pulses generated and the speed is
                                 proportional to the frequency of these pulses.
A basic stepper motor has a permanent magnet and/or an iron rotor,
together with a stator. The torque required to rotate the stepper
motor is generated by switching (commutating) the current in the
stator coils as illustrated below.

              Simplified concept of stepper motor operation                                                               DC Servo motor actuators, please see our
                                                                                                                 actuator section that starts on page 357 for details.


                                                                                  Simplified concept of DC motor operation
                                                                                  To describe the operation of a DC motor, consider the single coil
                                                                                  example shown above.
                                                                                  In this diagram, current is forced through the coil via sliding
                                                                                  contacts (brushes) that are connected to the voltage source. The
                                                                                  brushes are located on the end of the coil wires and make a
 Stepper motor actuator, please see our actuator
                                                                                  temporary electrical connection with the DC supply. When
 section that starts on page 357 for details.                                     current is flowing, a magnetic field is set up as shown.
                                                                                  At 0 degrees rotation, the brushes are in contact with the voltage
                                                                                  source and current is flowing. The current that flows through the
                                                                                  wire from A to B interacts with the magnetic field and produces
                                                                                  an upward force. The current that flows from C to D has a similar
Simplified concept of stepper motor operation                                     effect, but because the flow is in the opposite direction with
Although only 4 stator poles are shown above, there are really                    respect to the magnetic field, the force is in the downward
numerous tooth-like poles on both the rotor and stator. The result is             direction. Both forces are of equal magnitude. At 180 degrees, the
that positional increments (steps) of 1.8 degrees can be achieved by              same phenomenon occurs, but segment A-B is forced down and
switching the coils i.e. 200 steps/rev. If the current through one coil           C-D is forced up. In the 90 and 270-degree positions, the brushes
is increased as it is decreased in another, the new rotor position is             are not in contact with the voltage source and no force is
somewhere between the two coils and the step size is a defined                    produced. In these two positions, the rotational kinetic energy
fraction of a full step (microstep). When used with the apt™ motor                of the motor keeps it spinning until the brushes regain contact.
controller, the smallest angular adjustment is 0.014 degrees,                     In reality, DC motors have several such coils, wound onto an
resulting in a resolution of 25,600 microsteps per revolution for a               armature, which produces a more even torque. The magnetic field
200 full step motor.                                                              is provided by an electromagnet.


    New OptoDC/ST Motor Drivers, See Page 331
   These new opto drivers are USB interfaced compact single channel motor drivers, designed to operate with a variety
   of DC brushed motors or stepper motors. They contain a full embedded controller and driver circuit and can be
   operated with and without a PC. The OptoDC driver unit is a direct replacement for the DCX-MC110B controller
   modules featured in earlier editions of the Thorlabs catalog. The OptoST driver has been designed for easy manual
   and automatic control of low power stepper motor actuators such as the Thorlabs ZST series. While compact in
   footprint (2.5" x 2" x 1.6"), these units offer a fully featured motion control capability including velocity profile
   settings, limit switch handling, “on-the-fly” changes in motor speed and direction. For more advanced operation
   control over the closed loop PID parameters and adjustment of settings such as lead screw pitch and gearbox ratio
   allows support for many different actuator configurations.


                                                                                                                                        Sales: 973-579-7227                             329
                        Motion Control
Translation Stages      Stepper & DC Servo Motors… A Brief Tutorial – Comparison
Motorized
Mirror Mounts                                                                                                point or “Home” position in order to improve
                           Comparison Summary                                                                the accuracy of the stage. Movement is allowed
Rotation Stages                                                                                              right through the switch.
                           DC Motors
3 Axis Flexure Stages      ■   When a Voltage is Applied, Turn in One Direction at a Fixed Speed             Home Position
& Accessories
                           ■   Optimized to Run at a Fixed, Usually High RPM                                 Each motor in the system has an associated
4, 5 & 6-Axis Stages       ■   Speed Can be Varied if a PWM Controller is Added                              electronic counter, which keeps a record of the
                           ■
                                                                                                             current position in microsteps (for stepper
Drive Electronics              Inexpensive and Commonly Available
& Auto-Alignment                                                                                             motors), or encoder counts (for brushed DC
                           ■   Available in Wide Range of Speeds and Power
Actuators &                                                                                                  motors). If the Control PC is requested to report
Adjusters                  ■   Not Suitable for Positioning Unless Some Kind of Position Feedback            the position, the value of this counter is converted
                               is Added as with the ODC001, on page 333                                      back into motion units. When the system is
                           ■   If the Applied Load is Greater than the Capacity of the Motor,                powered up, the counters in the controller are all
                               the Motor Will Stall and Possibly Burn Out                                    set to zero and consequently, the system has no
                                                                                                             way of knowing the position of the stage in
                           Stepper Motors                                                                    relation to any physical datum. A datum can be
                           ■   Can Not Turn Without a Controller, such as the OST001 on page 332             established by sending all the motors to their
                           ■   Inexpensive and Commonly Available                                            “Home” positions. The “Home” position is set
                           ■
                                                                                                             during manufacture and is determined by driving
                               Available in Wide Range of Speeds and Power
                                                                                                             the motor until the negative limit switch is
                           ■   Precise Positioning Possible. Encoder Feedback Can be Used in Some Cases
                                                                                                             reached and then driving positively a fixed
                           ■   Torque is Highest at the Full Stop and Decreases as Speed is Increased        distance (zero offset). When at the “Home”
                           ■   If the Applied Load is Greater than the Capacity of the Motor,                position the counters are reset to zero thereby
                               the Motor Will Not Step, Thereby Making Precise Positioning                   establishing a fixed datum.
                               no Longer Possible
                                                                                                             Note: During a manual move, (i.e. if the motor
                                                                                                             shaft is turned by hand) no signal is sent to the
                                                                             Velocity Profiles               motor, the counter is not updated and any
                                                                             To prevent the motor from       subsequent position reporting will be false until
                                                                             stalling, it must be ramped up  the motor is “Homed”.
                                                                             gradually to its maximum velocity.
                                                                             Certain limits to velocity
                                                                             and acceleration result from
                                                                             the torque and speed limits
                                                                             of the motor, and the        We help you
                                                                             inertia and friction of the
              Graph of a trapezoidal velocity profile                        parts it drives. The motion  Precision Motion Control
                                                                             employed is described by a
                       trapezoidal velocity profile, reflecting the shape of the velocity vs. time graph  for basic research,
                       (shown above), thereby driving the stage to its destination as quickly as
                       possible, without causing it to stall or lose steps. The stage is ramped at        industrial R&D,
                       acceleration “a” to a maximum velocity “v”. As the destination is
                                                                            approached, the stage is      and high precision
                                                                             decelerated at “a” so that
  Stage limit switches                                                       the final position is        manufacturing...
                                                                             approached slowly in a
                                                                             controlled manner.             See   Page 274 for Details
                                                                         Limit Switches
                                                                         Linear and rotary stages
                                                                         can both contain                                                              MAX342
                                                                                                                                                         Patented
                                                                         microswitches that                                                            6,467,762
                                                                         detect certain
                                                                         positions of the stage,
                                                                         but they typically differ
                                                                        in the way these switches
                        are used. Most linear stages have limit switches to prevent the stage
                        from accidentally being moved too far in either direction. Once this
                        switch is activated the movement of the stage should halt. A limit switch
                        can also provide a physical datum used to define a “Home” position. A
                        rotary stage typically has only one switch, used to provide a reference           Put it all together
330                     Sales: 973-579-7227

				
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