BACKGROUND

In today's aviation industry, most pilots receive a great deal of flight training in flight simulators. For this training to be effective, flight simulators must be able to accurately replicate the static and dynamic “feel” of cockpit flight controls under normal and abnormal conditions.

The portion in a flight simulator responsible for replicating this feel is commonly referred to as a “control loading system.” This system generally consists of a force-generating device, known as a control loader, a servo drive, and a model of the aircraft flight control system which simulates the aircraft “feel” forces.

Control loaders are typically electro-mechanical devices containing an electric motor and, if the motor is brushless, a commutation transducer. Servo drives are a special type of electronic amplifier formed from a combination of electrical hardware, firmware and/or software. Aircraft models define the specific behavior of each flight control system and, most often, are generated in a separate control loading computer.

The control loader and servo drive work in concert to establish performance and fidelity capabilities of a given control loading system. Consequently, the design and integration of these items sharply distinguish one system from another and determine which systems are appropriate for specified FAA simulation certification levels—the highest being Federal Regulation 14 CFR Part 60, Level D, or equivalent.

SUMMARY

Unfortunately, current high-fidelity control loaders tend to be large, heavy, and expensive, making them difficult to use in many applications. The size and weight of prior control loaders have been primarily driven by motor requirements. For example, in order to generate the required force levels, dynamic fidelity, and stable, smooth (level D) performance, prior control loaders have employed large and expensive slotless motors. Such slotless motors tend to provide very smooth responses and low cogging, i.e., non-linear torque ripple, which can impair loader fidelity and feel. To accommodate the large motors, prior control loaders have also employed large and expensive motor mounting hardware, large and heavy motor/gear reduction methods, and cumbersome externally mounted force transducers.

In contrast with prior designs, an improved technique for control loading employs a slotted motor having a higher power density than slotless motors of similar power. The use of smaller slotted motors enables more efficient mounting hardware, smaller gear reduction mechanisms, and more efficiently mounted force transducers. Although slotted motors generally produce more cogging than slotless motors, the improved technique overcomes cogging and smooths the torque response by combining high-gain servo control with high-resolution motor sensing. Slotted motors are thus enabled to perform at a level previously achieved only with slotless motors, but with dramatic reductions in size, weight, and cost.

Given the smaller footprint and lower cost, the improved loader may also be practical in lower-cost simulators and as secondary controls in higher-cost simulators, applications where high fidelity has heretofore been difficult to achieve due to size and cost.

Certain embodiments are directed to a control loading system that includes a slotted motor having a motor shaft and an encoder configured to measure an angle of the motor shaft, an output arm coupled to the motor shaft and including a force transducer configured to measure an applied force applied by an operator, and a control stage. The control stage is configured to: receive inputs for (i) the applied force, (ii) the angle of the motor shaft, and (iii) a modeled force generated by a flight-control model; produce a command velocity based on a difference between the applied force and the model force; and generate, based on the inputs and on the command velocity, an output drive coupled to the slotted motor for driving the slotted motor.

In some examples, the control stage is further configured to apply a motor pole map to generate a cogging-correction based at least in part on (i) the angle of the motor shaft and (ii) the command velocity. According to some examples, the motor pole map includes an adaptive lookup table.

In some examples, the control stage is further configured to differentiate the angle of the slotted motor to generate a measure of angular velocity of the slotted motor, and generation of the output drive is further based at least in part on the measure of angular velocity of the slotted motor.

In some examples, the control stage includes multiple weighted differentiator elements configured to operate over respective time intervals, and the measure of angular velocity of the slotted motor is based at least in part on a sum of outputs of the weighted differentiator elements. According to some examples, weights of the weighted differentiator elements are established to optimize suppression of quantization noise introduced by the encoder.

According to some examples, the control stage is further configured to: generate a measure of command position as an integration of the command velocity; generate an error between the measure of command position and the angle of the motor shaft; and differentiate the error to produce a differentiated error, where the output drive is further based on the differentiated error.

In some examples, the control stage configured to differentiate the error includes multiple weighted differentiator elements configured to operate over respective time intervals, wherein the differentiated error is based at least in part of a sum of outputs of the weighted differentiator elements. According to some examples, weights of the weighted differentiator elements are configured to suppress quantization noise introduced by the encoder.

Other embodiments are directed to a method of control loading. Still other embodiments are directed to a computer program product. The computer program product stores instructions which, when executed on control circuitry of a computerized apparatus, cause the computerized apparatus to perform a method of control loading.

The foregoing summary is presented for illustrative purposes to assist the reader in readily grasping example features presented herein; however, this summary is not intended to set forth required elements or to limit embodiments hereof in any way. One should appreciate that the above-described features can be combined in any manner that makes technological sense, and that all such combinations are intended to be disclosed herein, regardless of whether such combinations are identified explicitly or not.

