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Geared Single Axis Actuator
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M-TEK positioners are mainly used for accurate positioning of optronic observation equipment and/or radar antennas for applications on land, sea and air platforms. The actuators may be direct-drive or geared (using anti-backlash gearboxes), and usually make use of permanent magnet, brushless DC torque motors. Resolvers are normally used as feedback sensors. The addition of slip rings will provide unlimited rotation. Power supplies, servo drives and controllers are enclosed in sealed enclosures located either externally, or on the positioners.
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DIRECT DRIVE SINGLE AXIS ACTUATORS
Direct drive actuators are usually used where:
1)high accuracy is important (no backlash),
2)inertial stabilisation is required (low friction), or
3)high rates are required.
Examples include an actuator for a Direction-finding Antenna (400 RPM maximum rate), and individual actuators to position each axis of a Radar Jamming system (inertial stabilisation). M-TEK uses Brushless DC motors, with resolver feedback. The resolver is used both for angle tell-back, and for commutation of the motor. Where high accuracy is required, dual-speed resolvers are used. Slip rings may be included (to allow continuous rotation), possibly including through-holes for RF rotary joints. The control electronics usually consists of a RISC Processor driving an IGBT power stage, to control the motor current, rate and angle. Specific modes (such as search patterns) can be provided, in addition to basic rate and position control.
DIRECT DRIVE DUAL AXIS POSITIONERS
These positioners make use of direct drive actuators. M-TEK has developed several elevation over azimuth direct-drive positioners and related control electronics, usually for radar and/or optronic tracking applications. Direct-drive motors are used to achieve high accuracy, fast dynamics and low friction. Dual-speed resolvers are used to accurately measure base-relative angles. Fibre-optic rate gyroscopes are used for sightline stabilisation.
One example is the positioner used for a naval Optronics/Radar tracker, which produces over 1000 Nm in azimuth and 500 Nm in elevation, in order to provide rapid large-angle slews and search patterns used by the radar. Tell-back accuracy is 0.25 mRad, and tracking accuracy normally better than 1 mrad. The control electronics includes DSP-based servo-amplifiers for the three-phase brushless motors, a power supply and a VME-based controller (using an off-the shelf CPU card and custom M-TEK I/O cards). The controller includes serial links to control the Customer-furnished optronics payloads (two thermal imagers, a laser
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Geared Single Axis Actuator
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rangefinder), receive data from the fibre-optic rate gyro, control the servos, read on-gimbal angles, and receive commands from the Radar Signal Processor.
A smaller system (100 Nm peak torque) has also been developed for an optronics tracker (with Customer-furnished daylight video camera, thermal imager, and laser rangefinder).
Both of the above systems are inertially stabilised using fibre-optic rate gyroscopes.
DIRECT DRIVE FOUR AXIS POSITIONERS
M-TEK has developed a sight using four direct-drive axes, for an Unmanned Aerial Observation System. This sight uses a dynamically tuned gyroscope to stabilise the limited-angle inner pitch and yaw axes, providing a sightline stabilization of 60 µRad. The outer pitch and roll axes follow-up, to keep the inner axes within their ranges of operation. The payload consists of a zoom lens with
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Direct Drive Single Axis Positioners
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monochrome video camera (optimised for the 650 to 900 nm band), and an eyesafe laser rangefinder. The control electronics includes power supplies, servo amplifiers, interface electronics to read angle and rate sensors and to control the camera/lens assembly and laser rangefinder, and a video autotracker. Total mass, including control electronics and cables, is 24 kg.
GEARED SINGLE AXIS ACTUATORS
Geared actuators are used where:
1)High torque is required from a small actuator.
2)Actuator and control electronics mass and power consumption must be minimised.
3)High maximum rates are not required.
4)Inertial stabilisation is not required (friction not critical).
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Direct Drive Single Axis Positioners
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M-TEK has produced geared single-axis actuators ranging from a small precision actuator used to position lens elements in a zoom camera, to a 500 Nm actuator used to point a large communications antenna at an aircraft. Zero-backlash gearboxes are used.
The 500-Nm actuator uses a dual-speed resolver for angle feedback, and a brushless motor to drive the gearbox. The dedicated control electronics includes the servo-amplifier, power supply, and the controller to track the aircraft using the error from the antenna.
GEARED DUAL AXIS POSITIONERS
M-TEK has produced a geared dual-axis elevation over azimuth positioner, for an observation system. Geared actuators are used to reduce the mass of the positioner and the electronics. Each actuator consists of a brushless motor driving a zero backlash gearbox. Resolvers are used for angle tell-back.
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Direct Drive Single Axis Positioner
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The control electronics (consisting of power supply, control CPU, conversion electronics, comms links and DSP-based servo-amplifiers) is mounted in the yoke of the positioner.
A second lightweight system is under development for use on a tripod.
MANUAL POSITIONERS
M-TEK has developed several manual positioners, used mainly for target cueing. The operator uses handles to point a cross-hair in the optics at a target, in order to report target azimuth and elevation angles. Smaller systems consist of a pair of binoculars mounted on a gimbal system which includes resolvers to measure azimuth and elevation angles. A slip ring in azimuth allows continuous rotation. Angles are reported either by resolver signals, or by a serial link.
A larger system includes a searchlight, and allows the binoculars to be replaced with a Night Observation Device. The searchlight is balanced to reduce the load on the operator. Control electronics on the positioner provides controls for the searchlight (such as on/off, black / white light and field-of-view switching) and displays angles. Angles and status are reported via a serial link.
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