Gimbal lock is a phenomenon which occurs in multi-gimbaled systems when two axes are driven into a coplanar
orientation, thereby resulting in the loss of one degree of rotational freedom. This paper presents a control
scheme which introduces a redundant fourth axis in conjunction with an algorithm that minimizes weighted
least-square gimbal rates, ultimately permitting the use of open inner and middle gimbals to achieve a wide
field of view. The control algorithm produces a singularity/gimbal lock measure which is derived using the inner
three gimbals, and used to adapt the weights and transition the table from three-axis operation to four-axis
operation at or near the three-axis gimbal lock orientation. Weight adaptation minimizes the peak gimbal rate
required to track a vehicle reference rate profile. The control strategy also minimizes tracking errors between
vehicle kinematic motion,which is obtained from the vehicle dynamics simulation, and kinematic motion induced
onto the table-mounted payload. The control algorithm accepts Euler angles and body rates, as defined in the
body fixed frame of reference, and generates four gimbal command sets. Each gimbal command set consists of
gimbal acceleration, rate, and angle. Mathematical analysis, simulation, and 3-D CAD multi-body dynamics
visualizations are included, illustrating differences between desired vehicle kinematic motion and that induced
by this control strategy onto the table mounted payload, including an examination of effects due to finite gimbal
control loop bandwidths.
Target Motion Simulators (TMS) are often used in conjunction with Flight Motion Simulators (FMS) to provide a realistic simulation of tracking and target engagement. For near-field applications, the TMS has typically been implemented with two additional gimbals around the FMS. For far-field applications, such as a radar, the TMS has traditionally been implemented with curvilinear X-Y Frames. A curvilinear frame placed at the proper distance from the FMS has the benefit of always pointing the Target back to the FMS intersection of axes. In most cases the curvilinear TMS provides good results. However, the curvilinear TMS lacks the possibility to change the distance between Target and Seeker, which is needed for operation with different radar wavelengths. Acutronic has developed a new approach using a flat frame (X-Y) TMS coupled with a gimballed payload mount that has the possibility of being used at various distances without losing the functionality of continuous pointing back to the seeker. This paper describes the electro-mechanical design and gives an overview of the Computer and Controllers used. It further addresses the problem of coordination transformation that is needed to obtain the correct pointing.
The increase in sophistication of shoulder and gun launched smart weapon systems have increased the demands placed on the flight motion simulator. The high spin rate and accelerations seen during launch drastically exceed the capability of the roll axes on today’s motion simulators. Improvements are necessary to the bearing and drive system to support these requirements.
This paper documents the requirements, design, and testing of a flight motion simulator produced to meet these challenges. This design can be incorporated into a new flight motion simulator, or as this paper describes, can be retrofitted into an existing flight motion simulator to improve its capability.
The effectiveness of a HWIL facility for developing missile guidance and targeting systems is limited by the quality of the elements that simulate the continuous physical processes. A motion simulator, which stimulates the inertial measurement and targeting sensors, must produce motion that is consistent with the actual physical processes. The effectiveness of a HWIL simulation is progressively degraded by each non-ideal element or process in the loop. The interface between the simulation computer and the motion system is traditionally a problematic link that is resolved once and for all in the Acutrol3000 Motion Control instrumentation.
This paper focuses on issues relating to data synchronization, time skew correction, multi-rate data smoothing, and reduced state motion vectors. Concepts are addressed and results are presented.