A visible light / infrared visual aircraft detection probe

Abstract

This invention discloses a visible light / infrared visual aircraft detection probe, comprising an imaging structure, a servo drive motor, and a control board for loading an inertial navigation system. The imaging structure includes an imaging unit, a gyroscope, and a drive frame. The imaging unit integrates an infrared camera, a visible light camera, and a laser ranging unit, achieving simultaneous imaging of the same target by staggered lens arrangement and optical axis consistency adjustment. This invention features a more compact overall structure, smaller size, lighter weight, smaller window volume, fewer intermediate components, and a simplified control process. Direct observation of the target using infrared and visible light eliminates image rotation, and the consistency of infrared, visible light, and optical axes can be adjusted. Visible light, infrared, laser, and gyroscope are all directly mounted on a rotating frame, with a pitch motor directly driving the frame and lens, resulting in fast response.

Description

Technical Field

[0001] This invention belongs to the field of aircraft detection technology and relates to a visible light / infrared visual aircraft detection probe. Background Technology

[0002] In recent years, with the rapid development of flight technology, including drones, their importance has become increasingly prominent in both the national economy and national defense; aerial photography is one of their important applications.

[0003] During continuous flight shooting, the tumbling and rolling motions caused by flight can create S-shaped image patterns, thus requiring stabilization of the shooting line of sight. Three-dimensional frame stabilization is a common solution used in many products. However, three-dimensional stabilization is very complex and suitable for large, high-value equipment, such as platform-based inertial navigation systems. Typical video or photographic stabilization systems cannot withstand this. Furthermore, due to the limited space available on the aircraft, the image acquisition unit used for shooting is prone to vibration, affecting the shooting results. Summary of the Invention

[0004] The technical problem solved by this invention is to provide a visible light / infrared visual aircraft detection probe that can conduct day and night reconnaissance at different altitudes and complete seamless photographic sampling of a predetermined area.

[0005] This invention is achieved through the following technical solution:

[0006] A visible light / infrared visual aircraft detection probe includes an image structure, a servo drive motor, and a control board for loading an inertial navigation system;

[0007] The shooting structure includes a shooting unit, a gyroscope, and a drive frame. The shooting unit integrates an infrared camera, a visible light camera, and a laser rangefinder. By staggering the lenses and calibrating the optical axis, the visible light and infrared cameras can shoot at the same target.

[0008] The drive frame is driven by a servo drive motor and includes a roll axis and a pitch axis. The roll axis is parallel to the roll axis of the flight vehicle and is equipped with a roll motor and a position encoder. The pitch axis is mounted on the roll axis. The pitch axis is parallel to the pitch axis of the flight vehicle. The stator of the pitch axis is a U-shaped frame structure, and a motor and a position encoder are mounted on both sides of the U-shaped frame. The imaging unit and the gyroscope that measures its inertial velocity are mounted on the pitch axis rotor. The gyroscope is directly sensitive to the aiming line of the imaging unit, and the aiming line of the imaging unit is viewed from below through the window glass set on the flight vehicle.

[0009] The gyroscope, servo drive motor, and control board motor form a closed-loop feedback to control the aiming line of the shooting unit, keeping the aiming line at a fixed position in inertial space. The control board receives data from the gyroscope, the position encoder, and the inertial navigation information, generates a PWM control signal, amplifies it through a power amplifier, and sends it to the drive motor for driving.

[0010] Aiming line stabilization is achieved through a combination of direct gyroscope stabilization and indirect inertial navigation system stabilization. Direct gyroscope stabilization has a high control bandwidth, while the attitude information provided by the inertial navigation system provides the absolute position information of the aiming line. Control commands are output from the control board to the servo drive motor, which drives the pitch / roll axis of the drive frame to rotate, eliminating the influence of flight disturbances on the aiming line.

[0011] The motion of the gyroscope-sensitive aiming line in inertial space is controlled by the control board, which outputs control commands to the servo driver. The servo driver reverses the drive frame to eliminate the influence of flight disturbances on the aiming line and can receive control commands to move at a certain speed.

[0012] The control board also applies equal and opposite angular motion to the drive frame via a servo driver to counteract image motion caused by flight translation, ensuring that the scene does not move relative to the image sensor during the exposure time, thus enabling reverse scan control.

[0013] The image motion velocity can be obtained from the velocity-to-altitude ratio of the flight vehicle. The velocity of the flight vehicle is obtained through the inertial navigation system.

[0014] V = V E COSΨ+V N SINΨ;

[0015] V E V is the eastward velocity of the flight vehicle. N Here, Ψ represents the northbound velocity, and Ψ represents the heading angle of the flight vehicle.

[0016] The flight altitude R is obtained by measuring distance with a laser rangefinder. Therefore, the velocity of the image motion caused by the translational motion of the flight vehicle is:

[0017] ω=V / R

[0018] The control board first controls the aiming line to work perpendicular to the ground, and then controls the image to be back-scanned at this speed according to the speed-height ratio. During the back-scanning process, it receives pulse signals sent by the host computer and issues control commands to expose the image by the shooting unit. After the exposure is completed, the drive frame returns to the initial position and then back-scans again.

[0019] The control board also receives zero-position correction commands sent by the host computer, which can set the azimuth and pitch zero position of the drive frame at any position within the working range.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] The visible light / infrared visual aircraft detection probe provided by this invention has a more compact overall structure, smaller size, lighter weight, smaller window size, fewer intermediate links, and simplified control process; it can directly observe targets with infrared and visible light without producing image rotation, and the consistency of infrared, visible light, and optical axis can be adjusted; it directly mounts visible light, infrared, laser, and gyroscope on a rotating frame, and the frame is directly driven by a pitch motor to drive the lens, resulting in fast response.

[0022] The visible light / infrared visual aircraft detection probe provided by this invention can achieve high-bandwidth control of the aiming line through gyro feedback, which plays an important role in attenuating high-frequency disturbances. Based on gyro feedback, attitude control of the aiming line can be achieved through inertial navigation data commands. The combination of the two can isolate base motion and torque disturbances and realize the system's backscan control function. At a relative altitude of 300m to 2000m, the visible light and infrared cameras are ensured to be pointing at the same target, and clear pictures can be taken at high speed relative to the ground. The difference between the start time of visible light and infrared imaging is less than 0.2ms. Infrared and visible light are separate modules, and the back intercept adjustment is convenient.

[0023] Simulations with and without gyroscope feedback showed little difference in the effects of base attitude changes on the two methods, but a significant difference in the effects on torque disturbances. Considering the complex torque disturbances caused by friction, winding torque, and vibration, only a stabilization system with direct gyroscope feedback can overcome these disturbances. High-bandwidth gyroscope feedback stabilization provides the system with a fast response capability, which is difficult to achieve with other methods, as proven by past engineering experience. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the imaging unit structure of the present invention; wherein, 101 is the optical load, 102 is the pitch axis, and 103 is the roll axis;

[0025] Figure 2 This is a schematic diagram of the drive frame stability control of the present invention;

[0026] Figure 3 This is a schematic diagram of the aiming line stabilization control of the present invention;

[0027] Figure 4 This is one of the exposure and imaging schematic diagrams of the present invention;

[0028] Figure 5 This is the second schematic diagram of the exposure and shooting process of the present invention;

[0029] Figure 6 This is a schematic diagram of the control board circuit connection of the present invention;

[0030] Figure 7 This is a schematic diagram of the pitch control model of the present invention;

[0031] Figure 8 This is a schematic diagram of the roll control model of the present invention. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to embodiments. These descriptions are for illustrative purposes only and are not intended to limit the scope of the invention.

[0033] See Figures 1-3 A visible light / infrared visual aircraft detection probe, comprising an imaging structure, a servo drive motor, and a control board for loading an inertial navigation system;

[0034] The shooting structure includes a shooting unit, a gyroscope, and a drive frame. The shooting unit integrates an infrared camera, a visible light camera, and a laser rangefinder. By staggering the lenses and calibrating the optical axis, the visible light and infrared cameras can shoot at the same target.

[0035] The drive frame is driven by a servo drive motor and includes a roll axis and a pitch axis. The roll axis is parallel to the roll axis of the flight vehicle and is equipped with a roll motor and a position encoder. The pitch axis is mounted on the roll axis. The pitch axis is parallel to the pitch axis of the flight vehicle. The stator of the pitch axis is a U-shaped frame structure, and a motor and a position encoder are mounted on both sides of the U-shaped frame. The imaging unit and the gyroscope that measures its inertial velocity are mounted on the pitch axis rotor. The gyroscope is directly sensitive to the aiming line of the imaging unit, and the aiming line of the imaging unit is viewed from below through the window glass set on the flight vehicle.

[0036] The gyroscope, servo drive motor, and control board motor form a closed-loop feedback to control the aiming line of the shooting unit, keeping the aiming line at a fixed position in inertial space. The control board receives data from the gyroscope, the position encoder, and the inertial navigation information, generates a PWM control signal, amplifies it through a power amplifier, and sends it to the drive motor for driving.

[0037] Aiming line stabilization is achieved through a combination of direct gyroscope stabilization and indirect inertial navigation system stabilization. Direct gyroscope stabilization has a high control bandwidth, while the attitude information provided by the inertial navigation system provides the absolute position information of the aiming line. Control commands are output from the control board to the servo drive motor, which drives the pitch / roll axis of the drive frame to rotate, eliminating the influence of flight disturbances on the aiming line.

[0038] The motion of the gyroscope-sensitive aiming line in inertial space is controlled by the control board, which outputs control commands to the servo driver. The servo driver reverses the drive frame to eliminate the influence of flight disturbances on the aiming line and can receive control commands to move at a certain speed.

[0039] The control board also applies an equal and opposite angular motion to the drive frame via a servo driver to counteract the image motion caused by flight translation, so that the scene does not move relative to the image sensor during the exposure time, thus enabling reverse scanning control.

[0040] The control board also receives zero-position correction commands sent by the host computer, which can set the azimuth and pitch zero position of the drive frame at any position within the working range.

[0041] The following is a detailed explanation of each part.

[0042] 1. Photograph the structure

[0043] To decouple the attitude motion of the flight vehicle and isolate the disturbance caused by the vibration of the flight vehicle platform, the shooting unit's line of sight is always kept vertically downward; furthermore, it can be oscillated as needed to compensate for the image shift caused by the imaging device under high speed and high ratio conditions. The shooting structure of this invention adopts an integrated design.

[0044] The infrared camera, visible light camera, and laser rangefinder are integrated into a single imaging unit. By arranging the lenses in a staggered manner and adjusting the optical axis for consistency (using a collimator to shoot targets at infinity), the visible light and infrared cameras can be aimed at the same target.

[0045] The drive frame employs a roll-and-tilt overall stabilization control system. The optical load (including a visible light camera and an infrared camera) is mounted on the pitch axis rotor of the rotatable drive frame (turntable). The gyroscope used to measure the inertial velocity of the optical load is mounted together with the optical load. The pitch axis is parallel to the pitch axis of the flight vehicle, and the aiming line of the optical load is viewed downwards through a window glass mounted on the flight vehicle.

[0046] The stator of the pitch axis is a U-shaped frame structure (see...). Figure 1 The U-shaped frame has a motor and a position encoder installed on each side; the pitch mechanism is installed on the roll axis, which is parallel to the roll axis of the flight vehicle. The movement of the roll axis actually generates the azimuth motion of the image; the roll axis is equipped with a roll motor and a position encoder.

[0047] By utilizing gyroscope closed-loop feedback, inertial stabilization of the image capture axis in both azimuth and pitch can be achieved, isolating the image motion blur caused by the attitude motion of the flight vehicle in the two directions of azimuth and pitch. However, the roll motion along the aiming line is uncontrolled.

[0048] At the same time, the frame structure will minimize the load through optimized load design.

[0049] 2. Servo Control

[0050] 2.1 The servo control performed by the control board mainly includes the following controls:

[0051] 1) Aiming line stabilization: In order to isolate the aiming line movement caused by the vibration and attitude change of the carrier aircraft, it is necessary to stabilize the aiming line by inertia. The image is stabilized by a closed-loop feedback system composed of gyroscopes and motors.

[0052] 2) Reverse scanning is used to eliminate image shift caused by the translation of the carrier aircraft and to enable the function of taking pictures at a certain frequency.

[0053] 3) Zero-position calibration: The zero-position calibration command sent by the host computer can set the azimuth and pitch zero position of the turntable to any position within the working range and save it in the memory.

[0054] 4) Report information by sending the frame angle, aiming line speed, and working status of the servo drive system to the host computer.

[0055] 2.2 Control Process

[0056] The roll motion of the image is caused by the directional motion of the flight vehicle. Let the directional motion speed of the flight vehicle be ω, the number of image pixels be a×b, and the image exposure time be t. Then, within the image exposure time, the location causing the greatest image blur is the pixel position farthest from the center of the viewing axis. For each pixel, the closer to the center of the visual axis, the less visual blur caused by image roll. For example, ω = 10 ° With an image size of 1024×768 pixels and an exposure time of 5ms, the maximum visual blur caused by the image roll is approximately 0.5 pixels. Therefore, the visual blur caused by the image roll is relatively small and acceptable in engineering, as long as the image is stabilized on both the position and pitch axes.

[0057] The motion blur in the azimuth and pitch directions is related to the focal length of the sensor. The longer the focal length, the greater the motion blur. Let the velocity of the azimuth or pitch direction caused by the motion of the flight vehicle be ω, the image exposure time be t, the focal length be f, and the pixel size be δ. Then the visual blur is ωtf / δ pixels. For example, if ω = 10° / s, the image exposure time is 5ms, the focal length is 25mm, and the pixel size is 14um, then the resulting visual blur is 1.5 pixels.

[0058] In addition, the translational motion caused by the flight of the aircraft will also cause motion blur in the image. If the flight speed of the aircraft is v and the distance between the aircraft and the target scene is d, then the resulting visual blur is vft / δd.

[0059] Therefore, it is necessary to control and eliminate image blur caused by the attitude motion and translation of the flight vehicle. A two-axis, two-frame structure is adopted, and the inertial stability of the aiming line is achieved through gyro feedback control, thereby reducing image blur caused by attitude motion. Meanwhile, the image blur caused by the translation of the aircraft is eliminated by controlling the backscan motion of the two-axis frame.

[0060] The stability control of the driving framework is as follows:

[0061] The optical system is directly mounted on the drive frame, and the gyroscope is mounted on the pitch axis, directly sensing the movement of the aiming line. The gyroscope senses the movement of the aiming line in inertial space, and the control board outputs control commands to the drive motor's driver. The drive motor causes the drive frame to reverse, eliminating the influence of external disturbances on the aiming line, and can also receive commands to move at a certain speed. The aiming line stabilization control employs active disturbance rejection control, improving the ability to suppress aiming line disturbances, thereby improving the system's stability and accuracy.

[0062] like Figure 3 As shown, in order to eliminate gyroscope drift and keep the aiming line in a fixed position in inertial space, the attitude output by the inertial navigation system is introduced to control the aiming line's inertial position.

[0063] Aiming line stabilization is achieved through a combination of direct gyroscope stabilization and indirect inertial navigation system (INS) stabilization. Direct gyroscope stabilization offers a high control bandwidth and effectively eliminates high-frequency disturbances, particularly image blurring caused by system vibrations. The INS provides attitude information that gives the aiming line absolute position information. Introducing INS data eliminates drift caused by gyroscope stabilization and controls the aiming line's position and attitude in inertial space. By combining the strengths of both methods, a better control effect can be achieved.

[0064] The reverse scan control is as follows:

[0065] To eliminate image blur caused by image shift due to the aircraft's translational motion, equal and opposite angular motions are applied to the two-axis inertial stabilization platform to counteract the image motion caused by translation. This ensures that the scene does not move relative to the image sensor during the exposure time, thus obtaining a clear image. This process requires the introduction of inertial navigation data and ranging information. Since images are only captured during vertical downward viewing, the image shift velocity can be obtained simply by calculating the flight vehicle's velocity-to-altitude ratio. The velocity is obtained through calculations using the inertial navigation output.

[0066] V = V E COSΨ+V N SINΨ;

[0067] V E V is the eastward velocity of the flight vehicle. N Ψ represents the northbound velocity and Ψ represents the heading angle of the flight vehicle.

[0068] The altitude R is obtained by measuring distance with a laser rangefinder. Therefore, the image motion velocity caused by the translational motion of the flight vehicle is approximately:

[0069] ω=V / R

[0070] During operation, the aiming line is first controlled to be perpendicular to the ground. Then, the image is back-scanned at this speed according to the speed-to-height ratio. During the back-scanning process, pulse signals are received to expose the image. After the exposure is completed, the image returns to the initial position and is back-scanned again.

[0071] 3. Shooting Process

[0072] Control system workflow diagram as follows Figure 4 , Figure 5 As shown: After the system is powered on, it defaults to standby mode and waits to receive working instructions. When a working instruction is received, it switches to working mode. At this time, the control system receives inertial navigation information, controls the aiming line to the vertical downward position, calculates the velocity-to-height ratio, and starts backscan. After receiving the exposure pulse instruction, it exposes an image for television or thermal imaging. After the exposure is completed, it drives the pitch frame to point back to a position perpendicular to the ground and restarts backscan.

[0073] The specific implementation methods of each component are given below.

[0074] MEMS gyroscopes are selected.

[0075] Table 1 Main Technical Parameters of the Gyroscope

[0076]

[0077]

[0078] The pitch encoder uses the eCoder20 magnetic grating encoder, and its technical specifications are as follows:

[0079] Table 2 Main Technical Parameters of Pitch Encoder

[0080]

[0081] The roll encoder selected is the eCoder35 magnetic grating encoder, with the following technical specifications:

[0082] Table 3 Main Technical Parameters of Roll Encoder

[0083]

[0084]

[0085] control board

[0086] The control board is the core of the entire system control. On one hand, it receives control commands from the host computer to control the servo mechanism and various sensors; on the other hand, it sends the operating status and data information to the host computer. For example... Figure 6 As shown, the control board receives gyroscope data, encoder data, and inertial navigation information, generates a PWM control signal, which is amplified by a power amplifier and sent to the drive motor for driving, thereby realizing functions such as stabilization and reverse scanning.

[0087] The control board includes a signal processor, interface circuit, motor drive circuit, memory circuit, and power management circuit. The processor is an ARM processor, the motor drive circuit uses an integrated power amplifier circuit, the circuit is simple and easy to control, and the memory uses an EEPROM circuit to store information such as the zero position.

[0088] 4. Simulation Analysis

[0089] 4.1 Establishing a system simulation model

[0090] The pitch inertia of the controlled object is J v =0.007kgm 2 The rolling moment of inertia is J h =0.01kgm 2 The pitch motor torque and back EMF coefficient are k T ≈k e ≈0.25, line resistance R=17 ohms, line inductance L=7mH, and the torque and back EMF coefficient of the roll motor are k. T ≈k e ≈0.18, line resistance R = 7 ohms, line inductance L = 2.8mH, gyroscope bandwidth approximately 230Hz, inertial navigation output bandwidth estimated at 20Hz, control models established as follows: Figure 7 and Figure 8 As shown.

[0091] Motion fuzzy analysis

[0092] Based on the flight conditions of the flight vehicle, at a relative altitude of 300m to 3000m and a relative ground speed of 40 to 60m / s, calculate the relative angular velocity at different speed-to-altitude ratios:

[0093] 40m 50m 60m 300m 7.628711569 9.527985174 11.42202758 600m 3.818586128 4.772239565 5.72523215 1000m 2.291694473 2.864403349 3.436969157 2000m 1.145961802 1.432425398 1.718871092 3000m 0.763988682 0.954977894 1.145961802

[0094] The maximum relative angular velocity is 11.42° / s. Based on the infrared exposure time of 7ms, the motion angle is 4.8′, which corresponds to 3.4 infrared pixels and 13.6 visible light pixels, resulting in a blurring effect.

[0095] At a height of 1km and a speed of 50m / s, the corresponding relative angular velocity is 2.86° / s. Based on an infrared exposure time of 7ms, the motion angle is 1.2′, corresponding to 0.85 infrared pixels and 3.4 visible light pixels. Therefore, the blur caused by infrared light is negligible, while the blur caused by visible light affects the imaging. This problem can be solved by further reducing the visible light exposure time, for example, to 1ms.

[0096] Simulation results show that, similar to the pitch direction, the ability to isolate base disturbances is not significantly different between the roll direction and the pitch direction with and without gyro feedback, but the ability to isolate disturbance torques differs considerably.

[0097] The simulation results are as follows:

[0098] 1) High-bandwidth control of the aiming line can be achieved through gyroscope feedback, which plays an important role in attenuating high-frequency disturbances.

[0099] 2) Based on gyroscope feedback, attitude control of the aiming line can be achieved through inertial navigation data commands. The combination of the two can isolate the base motion and torque disturbance, and realize the system's anti-scan control function.

[0100] The stabilization system constructed by direct gyroscope feedback can overcome the complex torque disturbances caused by friction, winding torque, and vibration. The high-bandwidth gyroscope feedback stabilization provides the system with a fast response capability, which is difficult to achieve with other methods. Previous engineering experience has fully demonstrated this point. Therefore, the direct gyroscope feedback method is more suitable for realizing the functions of this system.

[0101] The embodiments given above are preferred examples for implementing the present invention, and the present invention is not limited to the above embodiments. Any non-essential additions or substitutions made by those skilled in the art based on the technical features of the present invention are within the protection scope of the present invention.

Claims

1. A visible light / infrared visual aircraft detection probe, characterized in that, This includes the control board for the imaging structure, servo drive motors, and loading inertial navigation system; The shooting structure includes a shooting unit, a gyroscope, and a drive frame. The shooting unit integrates an infrared camera, a visible light camera, and a laser rangefinder. By staggering the lenses and calibrating the optical axis, the visible light and infrared cameras can shoot at the same target. The drive frame is driven by a servo drive motor and includes a roll axis and a pitch axis. The roll axis is parallel to the roll axis of the flight vehicle and is equipped with a roll motor and a position encoder. The pitch axis is mounted on the roll axis. The pitch axis is parallel to the pitch axis of the flight vehicle. The stator of the pitch axis is a U-shaped frame structure, and a motor and a position encoder are mounted on both sides of the U-shaped frame. The imaging unit and the gyroscope that measures its inertial velocity are mounted on the pitch axis rotor. The gyroscope is directly sensitive to the aiming line of the imaging unit, and the aiming line of the imaging unit is viewed from below through the window glass set on the flight vehicle. The gyroscope, servo drive motor, and control board motor form a closed-loop feedback to control the aiming line of the shooting unit, keeping the aiming line at a fixed position in inertial space. The control board receives data from the gyroscope, the position encoder, and the inertial navigation information, generates a PWM control signal, amplifies it through a power amplifier, and sends it to the drive motor for driving. Aiming line stabilization is achieved through a combination of direct gyroscope stabilization and indirect inertial navigation system stabilization. Direct gyroscope stabilization has a high control bandwidth, while the attitude information provided by the inertial navigation system provides the absolute position information of the aiming line. Control commands are output from the control board to the servo drive motor, which drives the pitch / roll axis of the drive frame to rotate, eliminating the influence of flight disturbances on the aiming line.

2. The visible light / infrared visual aircraft detection probe as described in claim 1, characterized in that, The motion of the gyroscope-sensitive aiming line in inertial space is controlled by the control board, which outputs control commands to the servo driver. The servo driver reverses the drive frame to eliminate the influence of flight disturbances on the aiming line and can receive control commands to move at a certain speed.

3. The visible light / infrared visual aircraft detection probe as described in claim 1, characterized in that, The control board also applies equal and opposite angular motion to the drive frame via a servo driver to counteract image motion caused by flight translation, ensuring that the scene does not move relative to the image sensor during the exposure time, thus enabling reverse scan control. The image motion velocity can be obtained from the velocity-to-altitude ratio of the flight vehicle. The velocity of the flight vehicle is obtained through the inertial navigation system. V=V E COSΨ+V N SINΨ; V E V is the eastward velocity of the flight vehicle. N Here, Ψ represents the northbound velocity, and Ψ represents the heading angle of the flight vehicle. The flight altitude R is obtained by measuring distance with a laser rangefinder. Therefore, the velocity of the image motion caused by the translational motion of the flight vehicle is: ω=V / R The control board first controls the aiming line to work perpendicular to the ground, and then controls the image to be back-scanned at this speed according to the speed-height ratio. During the back-scanning process, it receives pulse signals sent by the host computer and issues control commands to expose the image by the shooting unit. After the exposure is completed, the drive frame returns to the initial position and then back-scans again.

4. The visible light / infrared visual aircraft detection probe as described in claim 1, characterized in that, The control board also receives zero-position correction commands sent by the host computer, which can set the azimuth and pitch zero position of the drive frame at any position within the working range.

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