Showing papers by "Saab Automobile AB published in 1996"

Phase compensation of rate limiters in JAS 39 Gripen

Abstract: For a modern aerodynamically unstable fighter, like the JAS 39 Gripen, the flight control system (PCS) typically provides 45° phase margin. Therefore rate limiting of control surfaces is an important issue. Software rate limiters are placed on the control servo commands in order to prevent the hydraulic servos from rate limiting. When a rate limiter is saturated, the phase shift drastically reduces the stability margins of the closed loop and increases the risk for pilot-induced oscillation (PIO). This paper describes a novel method for compensating the phase shift of a rate limiter. In contrast to earlier phase compensation methods, this method uses feedback instead of logic or feedforward. Open loop and closed loop properties of the method are discussed. The method gives a drastic improvement on stability margins and reduces PIO tendencies. This is demonstrated on a JAS 39 Gripen example. Phase compensated rate limiters are now used in the JAS 39 Gripen PCS production software. Their effects on closed loop stability and flying qualities are discussed in the paper.

Phase compensation of rate limiters in unstable aircraft

Abstract: For a modern aerodynamically unstable fighter, like the JAS 39 Gripen, the flight control system typically provides 45/spl deg/ phase margin. Therefore rate limiting of control surfaces, which may cause large phase shifts, is an important issue. Software rate limiters are placed on the control servo commands in order to prevent the hydraulic servos from rate limiting. When a rate limiter is saturated, the phase shift drastically reduces the stability margins of the closed loop and increases the risk for pilot-induced oscillation (PIO). This paper describes a novel method for compensating the phase shift of a rate limiter. In contrast to earlier phase compensation methods, this method uses feedback instead of logic or feedforward. Open loop and closed loop properties of the method are discussed. The method gives a drastic improvement on stability margins and reduces PIO tendencies.

Occupational dermatoses in a Swedish aircraft plant.

Abstract: A survey of occupational dermatoses, based on a questionnaire, clinical examination and patch testing, was carried out among 341 workers in an aircraft plant. The questionnaire was answered by 330 workers (96.8%). Present or previous skin disease was reported by 92 employees, who were all subjected to physical examination and patch testing. Patch testing was conducted with a standard series, as well as with a series of substances and products representing the work environment. Occupational contact allergies were established in 12 employees. In total, the figure for occupational skin diseases was 16.1% (55 workers), when calculated for all employees.

Clock signal distribution and synchronisation in a digital system

Abstract: The invention relates to a method and a device for increasing the working speed of synchronous digital systems comprising a number of system parts (A - D) placed at a distance from each other and communicating with at least one other of the other system parts. A common signal for the system with a reference frequency (2) is distributed to all the system parts. The system parts are each equipped with their own internal clock signal oscillator (5) which is phase-adjusted individually for the different system parts in relation to the signal received from the reference frequency (2) so that the communication between the communicating system parts takes place with the same phase relationship but can take place in different periods.

Memory structure for storage of memory vectors

Abstract: A memory structure for storing memory vectors in at least one storage location. A plurality of storage locations store memory vectors. After configuration each storage location has a length adapted to a length of a memory vector stored therein. The storage locations are arranged parallel to each other and extend from a memory input deeper into the memory such that each memory vector is arranged to be undividedly stored in sequential order with a beginning of a vector at the memory input. Storage place addressing is made to the memory input. Input buffers are arranged to input the memory vectors in unbroken sequence according to the addressing. The vectors are inputted in a buffer-by-buffer manner. Output buffers are arranged to output the memory vectors in unbroken sequence according to the addressing in a buffer-by-buffer manner.

Climatizing arrangement and a method for controlling the same

Abstract: The present invention relates to a climatizing arrangement and to a method for controlling a climatizing arrangement, preferably air-conditioning equipment, for adjusting the temperature in the interior (7) of a vehicle, with individual regulation of the temperature of the air to different outlets (5, 6). The climatizing arrangement consists of an air-conducting system (2, 3, 4), a fan (1) for generating an air flow and a heat exchanger (8) for heating the air in cold weather. In warm weather the heat exchanger (8), in this case switched off, is instead utilized to provide flow resistance. The partial air flow to each outlet (5, 6) is then caused to pass through the heat exchanger or to bypass the heat exchanger (8), so that the flow rate is reduced in each air flow. Individual exhaust rates, and thus subjective sense of temperature, is thus obtained for each outlet (5, 6).

Method of identifying the combustion chamber of a combustion engine that is in the compression stroke, and a method and device for starting a combustion engine

Abstract: A combustion engine comprises at least two combustion chambers and an ignition system having a spark device (11, 13) forming an electrode gap and a charging member (20) for accumulating the electrical energy necessary for generating a spark in the electrode gap. The combustion chambers are in the compression stroke according to a predetermined sequence. During a first engine revolution, high voltage pulses are supplied at a high frequency to all spark devices (11, 13). The spark voltage in the electrode gap of each spark device (11, 13) is measured for each spark. Based on the measured spark voltage of the different spark devices, the combustion chamber that first will be in the compression stroke is determined by means of an electronic control unit (3). Based on the predetermined sequence and the knowledge of the combustion chamber that first is in the compression stroke, fuel is injected in the combustion chamber that next will be in the compression stroke.

Convertible roof stowage compartment lid

Abstract: The convertible vehicle has a stowage area (10) for the retracted hood behind the passenger compartment. Covering the area is a lid (14) connected with the body (4) by two hinge arms (16) which are fixed to the lid by screws (22). A cross-tie rod (24) is connected by separate points to the same hinge arms. A pair of restraint straps (36) connect the lid to the rod. Should the vehicle be hit from the rear, the lid may break free from its fasteners whereupon the restraint straps would limit its movement.

A Spinning Finite Beam Element of General Orientation Analyzed With Rayleigh/Timoshenko/Saint-Venant Theory

Abstract: Linear vibrations are studied for a straight uniform finite beam element of general orientation spinning at a constant angular speed about a fixed axis in the inertial space. The gyroscopic and circulatory matrices and also the geometric stiffness matrix of the beam element are presented. The effect of the centrifugal static axial load on the bending and torsional dynamic stiffnesses is thereby accounted for. The Rayleigh/Timoshenko/Saint-Venant theory is applied, and polynomial shape functions are used in the construction of the deformation fields. Nonzero off-diagonal elements in the gyroscopic and circulatory matrices indicate coupled bending/shearing/torsional/tensional free and forced modes of a generally oriented spinning beam. Two numerical examples demonstrate the use and performance of the beam element.

Parallel implicit time-accurate Navier-Stokes computations using a coarse grid correction scheme

Abstract: A parallel implicit Navier-Stokes solver is constructed using a block-by-block inversion of the resulting linear system of equations followed by a global coarse grid correction to account for the block coupling. This solver is used to compute two different cases of vortex shedding flows. The efficiency of our method is compared to the efficiency of the method based on pseudotime stepping and multigrid acceleration. This comparison is based on direct comparison of the two methods applied to identical test cases, as well as results reported in the literature. Emphasis is put on scalability as well as mesh sensitivity. It is concluded that the solver is not sensitive to grid stretching and scales well with both problem size and number of processors

Vehicle circuit for controllable, continuous engagement of electric load

Abstract: The engagement voltage is obtained from a current source (+30), while a control switch (2) is in series with the load (1). There is pulse current circuit (6) for intermittent voltage engagement of the load when the control switch is conductive. The voltage engagement is actuated by a control switch (4), affected by the pulse current circuit and series-connected to first control switch. A detection circuit (3,5) is in series with the load, scanning the current of the load, and fitted for actuating the switch-on of a holding circuit (16) for keeping the second control switch closed, when the detection circuit operates.

Compact prism-based optics for two-axis gimbal systems allowing large aperture and field of regard

Abstract: This paper presents an optical principle based on four right angle prisms with an optional intermediate lens that allows a large aperture combined with a large field of regard. The optics can be fitted into a small volume and the major part of the thermal imager is placed off-gimbal.

Object recognition by the use of a hand scanner and Fourier transform

Abstract: In autonomous manufacturing systems an important task is to recognize different 3D objects, e.g. workpieces. We have used the fact that different objects scatter laser light from a handscanner differently. To recognize the differences of the scattered light from the objects we have used Fourier transformation. It turns our that by using Fourier transformation we are able to recognize different objects and that this methods is a rather simple and inexpensive way to complement other object recognition systems, e.g. in robotic application.

A method for the measurement of relatively small water depths, especially in the vicinity of sea coasts and lake shores

Abstract: A method for measuring relatively small water depths is described. Measuring equipment for transmission having a direction in a small angle α to the perpendicular of the water depth and for receiving laser pulses of μ = about 0.5 νm is used. A first reflection from the water surface is obtained and a second reflection from the bottom. By means of signal processing the signals corresponding to the reflections the water depth is calculated. In particular, the method is characterized in that the signal processing is made in such a way that the function signal-amplitude/time is scanned and a first portion of this function is approximated by a substantially straight first line, after which the function is further scanned to pass through a minimum of its first derivative (inflection point) to a second increasing portion of the function located before a maximum point, which is approximated by a substantially straight second line, whereafter the time interval between the lines that is related to said distance is used for determining it.