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Compact Direct Drive Rotation Mount
Ø1" Linear Film Polarizer in a CRM1 Rotation Mount and Ø1/2" Film Polarizer Threaded into the DDR25 Motorized Rotation Mount
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The rear face of the rotation stage (shown) has four stationary tapped holes for 16 mm cage system rods. A 30 mm cage system can be continued from the back side of the stage by using an SP05 30 mm to 16 mm Cage Adapter Plate.
Thorlabs’ DDR25(/M) low-profile, direct-drive rotary mount provides continuous rotation of a load with a moment of inertia up to 70 kg•mm2 with a maximum rotation speed of up to 5.0 Hz (1800 °/s). An SM05 (0.535"-40) threaded central aperture allows an optical path to pass directly through the body of the mount and provides compatibility with Ø1/2" optical elements and Ø1/2" lens tubes. Components can be threaded into this bore from either side of the rotation mount.
The DDR25(/M) has a 3-phase, slotless, brushless DC motor integrated directly into the frame of the stage. This eliminates all forms of mechanical transmission, resulting in high repeatability, rigidity and reliability. The winding design enables good velocity stability, even at low speeds, by eliminating torque ripple due to magnetic cogging. The optical encoder has a 4.3 µrad theoretical resolution and provides high accuracy and repeatability, while the precision-engineered bearings and tight manufacturing tolerances produce low axial wobble. An engraved graduated scale with 2° increments allows for coarse positioning.
The mount is designed to be mounted vertically on a post using one of four 8-32 (M4) taps on the sides of the device. The rotating portion of the front face features four 4-40 tapped holes spaced for integration of 16 mm cage system assemblies and components, allowing for the rotation of a cage segment. The non-rotating portion of the front face also includes four 4-40 tapped holes spaced for use with 30 mm cage system components. The back of the device features four more 4-40 tapped holes for 16 mm cage system rods, but this portion of the cage remains stationary. A stationary 30 mm cage system can be continued on the back side of the stage using an SP05 30 mm to 16 mm cage adapter plate, as shown in the image to the right. The position of all of these tapped holes can be seen in the diagram below.
The stage is driven by the KBD101 brushless DC controller (sold separately below), which provides very precise positioning through the stable closed-loop PID control system (see the PID Tutorial tab for more information). The controller ships with our Kinesis and legacy APT software packages for easy integration into an existing system. Power supplies for the K-Cube™ controller are sold separately (see below).
The cable attached to the DDR25(/M) rotation stage is terminated in a male 15-pin D-type connector. Pin details are given below.
Thorlabs offers two platforms to drive our wide range of motion controllers: our Kinesis® software package or the legacy APT™ (Advanced Positioning Technology) software package. Either package can be used to control devices in the Kinesis family, which covers a wide range of motion controllers ranging from small, low-powered, single-channel drivers (such as the K-Cubes™ and T-Cubes™) to high-power, multi-channel, modular 19" rack nanopositioning systems (the APT Rack System).
The Kinesis Software features .NET controls which can be used by 3rd party developers working in the latest C#, Visual Basic, LabVIEW™, or any .NET compatible languages to create custom applications. Low-level DLL libraries are included for applications not expected to use the .NET framework. A Central Sequence Manager supports integration and synchronization of all Thorlabs motion control hardware.
Kinesis GUI Screen
APT GUI Screen
Our legacy APT System Software platform offers ActiveX-based controls which can be used by 3rd party developers working on C#, Visual Basic, LabVIEW™, or any Active-X compatible languages to create custom applications and includes a simulator mode to assist in developing custom applications without requiring hardware.
By providing these common software platforms, Thorlabs has ensured that users can easily mix and match any of the Kinesis and APT controllers in a single application, while only having to learn a single set of software tools. In this way, it is perfectly feasible to combine any of the controllers from single-axis to multi-axis systems and control all from a single, PC-based unified software interface.
The software packages allow two methods of usage: graphical user interface (GUI) utilities for direct interaction with and control of the controllers 'out of the box', and a set of programming interfaces that allow custom-integrated positioning and alignment solutions to be easily programmed in the development language of choice.
A range of video tutorials is available to help explain our APT system software. These tutorials provide an overview of the software and the APT Config utility. Additionally, a tutorial video is available to explain how to select simulator mode within the software, which allows the user to experiment with the software without a controller connected. Please select the APT Tutorials tab above to view these videos.
Thorlabs' Kinesis® software features new .NET controls which can be used by third-party developers working in the latest C#, Visual Basic, LabVIEW™, or any .NET compatible languages to create custom applications.
For a collection of example projects that can be compiled and run to demonstrate the different ways in which developers can build on the Kinesis motion control libraries, click on the links below. Please note that a separate integrated development environment (IDE) (e.g., Microsoft Visual Studio) will be required to execute the Quick Start examples. The C# example projects can be executed using the included .NET controls in the Kinesis software package (see the Kinesis Software tab for details).
These videos illustrate some of the basics of using the APT System Software from both a non-programming and a programming point of view. There are videos that illustrate usage of the supplied APT utilities that allow immediate control of the APT controllers out of the box. There are also a number of videos that explain the basics of programming custom software applications using Visual Basic, LabView and Visual C++. Watch the videos now to see what we mean.
To further assist programmers, a guide to programming the APT software in LabView is also available.
The PID circuit is often utilized as a control loop feedback controller and is very commonly used for many forms of servo circuits. The letters making up the acronym PID correspond to Proportional (P), Integral (I), and Derivative (D), which represents the three control settings of a PID circuit. The purpose of any servo circuit is to hold the system at a predetermined value (set point) for long periods of time. The PID circuit actively controls the system so as to hold it at the set point by generating an error signal that is essentially the difference between the set point and the current value. The three controls relate to the time-dependent error signal; at its simplest, this can be thought of as follows: Proportional is dependent upon the present error, Integral is dependent upon the accumulation of past error, and Derivative is the prediction of future error. The results of each of the controls are then fed into a weighted sum, which then adjusts the output of the circuit, u(t). This output is fed into a control device, its value is fed back into the circuit, and the process is allowed to actively stabilize the circuit’s output to reach and hold at the set point value. The block diagram below illustrates very simply the action of a PID circuit. One or more of the controls can be utilized in any servo circuit depending on system demand and requirement (i.e., P, I, PI, PD, or PID).
Through proper setting of the controls in a PID circuit, relatively quick response with minimal overshoot (passing the set point value) and ringing (oscillation about the set point value) can be achieved. Let’s take as an example a temperature servo, such as that for temperature stabilization of a laser diode. The PID circuit will ultimately servo the current to a Thermo Electric Cooler (TEC) (often times through control of the gate voltage on an FET). Under this example, the current is referred to as the Manipulated Variable (MV). A thermistor is used to monitor the temperature of the laser diode, and the voltage over the thermistor is used as the Process Variable (PV). The Set Point (SP) voltage is set to correspond to the desired temperature. The error signal, e(t), is then just the difference between the SP and PV. A PID controller will generate the error signal and then change the MV to reach the desired result. If, for instance, e(t) states that the laser diode is too hot, the circuit will allow more current to flow through the TEC (proportional control). Since proportional control is proportional to e(t), it may not cool the laser diode quickly enough. In that event, the circuit will further increase the amount of current through the TEC (integral control) by looking at the previous errors and adjusting the output in order to reach the desired value. As the SP is reached [e(t) approaches zero], the circuit will decrease the current through the TEC in anticipation of reaching the SP (derivative control).
Please note that a PID circuit will not guarantee optimal control. Improper setting of the PID controls can cause the circuit to oscillate significantly and lead to instability in control. It is up to the user to properly adjust the PID gains to ensure proper performance.
The output of the PID control circuit, u(t), is given as
From here we can define the control units through their mathematical definition and discuss each in a little more detail. Proportional control is proportional to the error signal; as such, it is a direct response to the error signal generated by the circuit:
Larger proportional gain results is larger changes in response to the error, and thus affects the speed at which the controller can respond to changes in the system. While a high proportional gain can cause a circuit to respond swiftly, too high a value can cause oscillations about the SP value. Too low a value and the circuit cannot efficiently respond to changes in the system.
Integral control goes a step further than proportional gain, as it is proportional to not just the magnitude of the error signal but also the duration of the error.
Integral control is highly effective at increasing the response time of a circuit along with eliminating the steady-state error associated with purely proportional control. In essence integral control sums over the previous error, which was not corrected, and then multiplies that error by Ki to produce the integral response. Thus, for even small sustained error, a large aggregated integral response can be realized. However, due to the fast response of integral control, high gain values can cause significant overshoot of the SP value and lead to oscillation and instability. Too low and the circuit will be significantly slower in responding to changes in the system.
Derivative control attempts to reduce the overshoot and ringing potential from proportional and integral control. It determines how quickly the circuit is changing over time (by looking at the derivative of the error signal) and multiplies it by Kd to produce the derivative response.
Unlike proportional and integral control, derivative control will slow the response of the circuit. In doing so, it is able to partially compensate for the overshoot as well as damp out any oscillations caused by integral and proportional control. High gain values cause the circuit to respond very slowly and can leave one susceptible to noise and high frequency oscillation (as the circuit becomes too slow to respond quickly). Too low and the circuit is prone to overshooting the SP value. However, in some cases overshooting the SP value by any significant amount must be avoided and thus a higher derivative gain (along with lower proportional gain) can be used. The chart below explains the effects of increasing the gain of any one of the parameters independently.
In general the gains of P, I, and D will need to be adjusted by the user in order to best servo the system. While there is not a static set of rules for what the values should be for any specific system, following the general procedures should help in tuning a circuit to match one’s system and environment. In general a PID circuit will typically overshoot the SP value slightly and then quickly damp out to reach the SP value.
Manual tuning of the gain settings is the simplest method for setting the PID controls. However, this procedure is done actively (the PID controller turned on and properly attached to the system) and requires some amount of experience to fully integrate. To tune your PID controller manually, first the integral and derivative gains are set to zero. Increase the proportional gain until you observe oscillation in the output. Your proportional gain should then be set to roughly half this value. After the proportional gain is set, increase the integral gain until any offset is corrected for on a time scale appropriate for your system. If you increase this gain too much, you will observe significant overshoot of the SP value and instability in the circuit. Once the integral gain is set, the derivative gain can then be increased. Derivative gain will reduce overshoot and damp the system quickly to the SP value. If you increase the derivative gain too much, you will see large overshoot (due to the circuit being too slow to respond). By playing with the gain settings, you can maximize the performance of your PID circuit, resulting in a circuit that quickly responds to changes in the system and effectively damps out oscillation about the SP value.
While manual tuning can be very effective at setting a PID circuit for your specific system, it does require some amount of experience and understanding of PID circuits and response. The Ziegler-Nichols method for PID tuning offers a bit more structured guide to setting PID values. Again, you’ll want to set the integral and derivative gain to zero. Increase the proportional gain until the circuit starts to oscillate. We will call this gain level Ku. The oscillation will have a period of Pu. Gains are for various control circuits are then given below in the chart.
Rotation Mount and Stage Selection Guide
Thorlabs offers a wide variety of manual and motorized rotation mounts and stages. Rotation mounts are designed with an inner bore to mount a Ø1/2", Ø1", or Ø2" optic, while rotation stages are designed with mounting taps to attach a variety of components or systems. Motorized options are powered by a DC Servo motor, 2 phase stepper motor, or an Elliptec™ resonant piezo motor. Each offers 360° of continuous rotation.
Manual Rotation Mounts
Manual Rotation Stages
Motorized Rotation Mounts and Stages
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Diagram Showing the Dimensions of the DDR25(/M) Rotation Stage and the Position of Tapped Holes for Cage System Rods
Characterized by high-speed rotation and high-positional accuracy, the DDR25(/M) mount is well-suited for applications where there is a need to rotate components at high speed within a cage or other system. This mount is driven by the KBD101 brushless DC controller (sold separately below), which provides precise positioning through the stable closed-loop PID control system.
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KCH601 USB Controller Hub (Sold Separately) with Installed K-Cube and T-Cube™ Modules (T-Cubes shown on the KAP101 Adapter)
Thorlabs' KBD101 K-Cube™ Brushless DC Motor Controller provides local and computerized control of a single motor axis. It features a top-mounted control panel with a velocity wheel that supports four-speed bidirectional control with forward and reverse jogging as well as position presets. A backlit digital display is also included that can have the backlit dimmed or turned off using the the top-panel menu options. The front of the unit contains two bidirectional SMC trigger ports that can be used to read a 5 V external logic signal or output a 5 V logic signal to control external equipment. Each port can be independently configured.
Please note that this controller does not ship with a power supply. Compatible power supplies are listed below. Additional information can be found on the main KBD101 Brushless DC Servo Motor Controller page.
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A location-specific adapter is shipped with the power supply unit based on your location. The adapters for the KPS101 are shown here.
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The KPS101 Power Supply Unit
The KPS101 power supply outputs +15 VDC at up to 2.4 A and can power a single K-Cube or T-Cube with a 3.5 mm jack. It plugs into a standard wall outlet.
The KCH301 and KCH601 USB Controller Hubs each consist of two parts: the hub, which can support up to three (KCH301) or six (KCH601) K-Cubes or T-Cubes, and a power supply that plugs into a standard wall outlet. The hub draws a maximum current of 10 A; please verify that the cubes being used do not require a total current of more than 10 A. In addition, the hub provides USB connectivity to any docked K-Cube or T-Cube through a single USB connection.
For more information on the USB Controller Hubs, see the full web presentation.