Description:1 Title of invention
Active side control stick assembly with variable force feedback.
2 Field of invention
The present invention of an active side control stick assembly with variable force feedback is related to the aircraft flight control column and is more particularly associated with the method of providing and controlling the tactile feedback force to the pilot following the stick displacement and aircraft dynamics.
3 Background of invention
Aircraft have been predominantly designed with two types of pilot interfaces: yokes and centre sticks. The yoke which is common on transport aircraft, has a large mass, which impedes rapid maneuvering and often visually obstructs a portion of the instrument panel. Majority of fighter aircraft are using centre sticks. Although the centre stick solves the two main disadvantages of the yoke, a few problems still exist. The stick can be fatiguing as a result of the large motion range. Furthermore, coupling problems can occur when the pilot attempts to make inputs to a single axis. Often, designers face difficulties to locate the centre stick in the cockpit in such a way that it should not hinder the pathway of the escape system during the emergency cockpit egress. This is a big challenge for the designers to cope up with all these constraints. To overcome the drawbacks of the centre stick, passive side stick was designed, developed and being used in several military and civil aircraft. Pilot uses wrist movements to operate the side stick and is more convenient to operate as compared to the centre stick.
The passive side stick obviates certain drawbacks of the centre stick. However, the passive side control stick provides a pre-determined fixed force feel characteristics. The passive side stick is composed of springs and dampers, which generate the force in relation to side stick displacement characteristics. The main disadvantage of the passive side stick is that it is bulky, it requires more space in the cockpit, and is isolated from the flight control surfaces. It provides the same force feel irrespective of the flight conditions. It doesn't provide tactile cues to the pilot to take corrective measures in case of emergency.
4 Brief Summary of invention
The primary objective of the present invention is to provide situational awareness to the pilots by varying the tactile force feedback on the control stick based on the real-time dynamic flight conditions of the aircraft.
The invention consists of outer gimbal (101), which provides longitudinal forward and aft stick displacement and an inner gimbal (108) provides lateral movements of the stick for left and right, which controls the roll rates of the aircraft. A control grip (107) is interfaced with the outer gimbal (101). The outer gimbal (101) is connected to a torque motor- pitch (102) via a lever (103) and a force sensor assembly (104). The outer gimbal (101) is also connected to an artificial feel unit-pitch (AFU) (105) to provide passive force feel and centering. A quadruplex linearly variable differential transducer(LVDT) assembly (106)is mounted on the AFU assembly (105) which senses the grip movement and converts it into proportional electrical output. The quadruple linearly variable differential transducer assembly (106) provides redundant electrical signals for longitudinal flight controls. In the lateral channel, the inner gimbal (108) is connected to a torque motor- roll (109) via a lever (111) and a force sensor assembly (112) and another lever (117). An artificial feel unit - roll (116) is connected to the inner gimbal (108) through a lever (110).A quadruplex linearly variable differential transducer assembly - roll (113) is assembled around the artificial feel unit - roll (116) which senses the grip movement in the roll and converts it into proportional electrical output. The quadruple linearly variable differential transducer assemblies (113) provides redundant electrical signals for lateral flight controls.
Another objective of the present invention is to provide different modes of operation such as active, passive, and jamming modes which ensures sufficient redundancy and failure management of this flight critical item.
Further objective of the present invention is to provide awareness to the pilot about the present flight conditions by providing cues such as stick shacking and stick pushing, when the aircraft approaches the flight limiting envelope.
The active side stick assembly with variable force feedback is coupled with the aircraft dynamics and it provides the tactile and visual cues allowing for better handling and reduced pilot workload. It also provides sufficient redundancy in case of failure of active mode. The mechanism is developed in a way that there is no cross-coupling between lateral and longitudinal axes. A control grip (107) is interfaced with the outer gimbal (101) of the present invention.
5 Brief description of drawings
Fig.1 shows the block diagram of the active side control stick assembly. It is comprising: a control grip (107), an outer gimbal (101), an inner gimbal (108), a plurality of force sensors (104) (112), a plurality of artificial feel units (105)(116), a plurality of quadruplex linearly variable differential transducer (LVDT) assembly(106) (113), a plurality of torque motors (102) (109),and electronic control board (115). The active side control stick assembly is interfaced with a flight control computer (126)) of the aircraft as shown in Fig. 1.
Fig.2 shows the perspective view of the active side control stick assembly. Fig.2 shows the control grip (107), boot assembly (120), rigging pin-pitch (121), rigging pin-roll (122), cover plates (123), and outlet of electrical pigtail connectors (124).
Fig.3 shows the internal details of the active side control stick assembly, showing the torque motor - pitch (102), the control grip (107), the inner gimbal (108), a modularized box assembly (114),the electronic control board (115),a roll bracket assembly(118), a roll Shaft(119),and a plurality of stop bolts (125).
Fig.4. shows the arrangement of the outer gimbal (101), the torque motor (102), a lever (103), a force sensor (104) in the pitch channel, the artificial feel unit (AFU)-pitch(105),the quadruplex pitch LVDT assembly(106),the control grip(107), and the inner gimbal(108).
Fig.5. shows the arrangement of the force sensor assembly - pitch (104), the artificial feel unit (AFU)-pitch (105), the control grip (107), the inner gimbal (108), the torque motor - roll (109), a plurality of levers (110) (111) (117), the roll force sensor (112), the quadruplex roll LVDT assembly (113), and the artificial feel unit- roll (116).
6 Detailed description of invention
The flight control system design aims to create a user-friendly aircraft with good handling qualities. This allows the pilot to concentrate on mission tasks instead of having to devote the effort towards compensating for poor handling qualities. Pilot workload is thus reduced and performance during mission tasks is improved.
The present invention provides an active side control stick (ASCS)assembly that is designed to reduce the movement of the arm and force feel of the pilot. It reduces the pilot effort required for normal flight maneuvers and reduces fatigue in long flight hours. It contains torque motors (102) (109) with encoder, quadruplex pitch and roll LVDTs (106) (113),and force sensor assemblies (104) (111) in pitch and roll axes. It facilitates both maneuvering and trimming of the aircraft. The present invention is mounted on right hand side of the cockpit in a single seater or tandem seater aircraft and either side of the pilot seats in the side by side cockpit configuration for efficient handling, maneuvering, and control of trainer/fighter/passenger aircraft and helicopters.
Refer to Fig. 1 and Fig.4 for the present invention. The Fig.1 shows block diagram of the active side control stick (ASCS).The present invention is used for longitudinal and lateral control of trainer, fighter, and civil aircraft that has a fly-by-wire type flight control system. The present invention consists of an outer gimbal (101)to provide longitudinal forward and aft stick displacement; and an inner gimbal (108) to provide lateral movements of the stick for left and right to control roll rates/roll attitude of the aircraft. The outer gimbal (101) is connected to a torque motor- pitch (102) via a lever (103) and a force sensor assembly (104). The outer gimbal (101) is also connected to an artificial feel unit-pitch (AFU) (105) to provide passive force feel and centering. A quadruplex linearly variable differential transducer (LVDT) assembly (106)is mounted on the AFU assembly (105) which senses the grip movement and converts it into a proportional electrical output. The quadruple LVDT assembly (106) provides the redundant electrical signals for longitudinal flight controls and these electrical signals are interfaced with a flight control computer(126) for further processing. The mechanism is developed such that there is no cross-coupling between lateral and longitudinal axes. A control grip (107) is interfaced with the outer gimbal (101) of the present invention.
An electronic control board (115) is used to obtain the real-time flight parameters, that include: calibrated air speed, altitude, attitudes, angle of attack, angle of sideslip, load factor, and control surface movements. Based on the flight envelope limits and control algorithms, the electronic board (115)calculates the feedback force that the pilot should feel for a given displacement of the stick. Accordingly, a proportional current will be sent to the torque motors (102) (109)to increase or decrease the pilot cues. The torque motors (102) (109) do not obstruct the control grip movements, rather they (102)(109) apply resistance to the grip (107) movements proportional to the flight conditions. The real-time stick position information in pitch and roll directly reaches the flight control computer (126) where the computer (126) manipulates the control surfaces to get the required flight attitude. The trim requirements and other switch functionalities of the grip (107) reach the flight control computer (126) directly. The other functionalities of the electronic board (115) include flight envelope awareness and envelope protection by providing the soft stops, stick shaking, and stick push functions in both longitudinal and lateral channels. If any of the active elements such as the torque motors (102)or the electronic board (115) fails, the passive mode AFU of pitch (105) and AFU of roll (116) provide the artificial feel to the pilot and the pitch and roll quadruplex LVDT assemblies (106) (113) provide the stick position information to the computer (126) without any hindrance and loss of signal. This mode is called passive mode. Similarly, in the stick jamming mode, if the gimbals (101) (108) get struck, the force sensors (104) (114) provide proportional electrical output to the electronic control board(115) and the computer (126). The computer (126) uses these signals to control the aircraft. In these three modes, namely, active, passive, and jamming, the active side control stick provides sufficient redundancy in the integrated flight control system of the aircraft.
Refer to Fig.5. The inner gimbal (108) provides lateral movements of the stick for left and right displacement which controls the roll axis of the aircraft. The roll channel of the active side control stick consists of the torque motor - roll (109), two lever assemblies (110) (111), and a force sensor assembly (112). A quadruplex roll LVDT (113) is mounted which senses the grip left and right movement and converts it into proportional electrical output.
In the preferred embodiment of the proposed invention, the integrated and modularized box assembly (114) houses all the pitch and roll channel units as shownin Fig.2. The movement of the control grip (107) is adjusted by adjusting the stop bolts (125) in both pitch and roll directions.
The electronic control board (115) receives the aircraft parameters like calibrated airspeed, angle of attack, angle of sideslip, attitude, and acceleration from the flight control computer (126)and modulates the feedback forces in both pitch and roll axis by controlling the torque of the motors (102) (109).TheLVDT(106) (113) output and force sensor (104) (112) output signals are interfaced with the flight control computer(126) either through a pigtail connector(124) or through a fixed connector on the control stick for further processing. The rotary variable differential transducer (RVDT) assembly is considered as an alternative to the LVDT assembly (106) (113) of the present invention.
The electronic control board (115) generates a control signal representative of the given stick movement and other flight conditions such as load factor, airspeed, pitch attitude, angle of attack, angle of sideslip, pitch rate, roll attitude, and roll rate for the control of the torque motors (102) (109). The electronic control board (115) with the help of LVDTs (106) (113), force sensors (104) (112), and torque motors (102) (109) generate different force - displacement characteristics, breakout forces, soft stops, surpass able back stops, hard stops, and feel slopes. The control board(115) manipulates the side stick dynamics such as damped natural frequency and damping as per the flight control laws and provides the angle of attack limit awareness and ‘g’ limit awareness to the pilot and has programmable features such as stick shaking and stick push functionalities . The present invention provides situational awareness to the pilots in an aircraft equipped with fly-by-wire type flight control system.
The electronic control board(115) generates differential feedback forces in the roll axis based on the arm kinematics and ergonomics, where the feedback force towards the left roll can be made slightly more than the right (for the case of right-hand side located stick). The control board(115) is also used to generate feedback forces of different slope (force versus displacement) curves with parameters that include breakout force, soft stop, and hard stop.
The present invention provides the angle of attack limit awareness to the pilot by stick shaking function and it provides ‘g’ (acceleration due to gravity)limit protection by automatic stick push function where the torque motors(102) (109) push the control grip (107) towards neutral position. Also, it provides the soft stops for ‘g’ limit protection and the awareness to the pilot by manipulating the current signal to the torque motors (102) (109) through the control board (115).
The control board(115)serves to excite the LVDTs(106) (113), force sensors(104) (112), and torque motors(102) (109); and receives the signals from these sensors (106)(113)(104)(112) for further processing.
The electronic control board(115) serves to control the back drive torque of the motors (102) (109)and vary the feedback forces as per the actual dynamics of the aircraft.
In an embodiment of the present invention for a twin-seater trainer aircraft, two active side control sticks are arranged in a dual-cockpit mode where the control board (115) duplicates the movements of the other stick based on the movements of the stick being operated by the pilot. This is to provide a method for automatically varying the biasing force on the grip(107) for proper pitch and roll control. The present invention ensures the improved reliability and redundancy such that the failure of active elements like torque motors(102) (109)does not affect the performance of the stick, since there is a passive artificial feel unit for the pitch and roll channels (105)(116)that provides the pilot a linearly increasing force feedback following the stick movement.
The present invention of the active side control stick assembly has three modes of operation, i.e., active mode, passive mode, and stick jamming mode to increase the redundancy. The It is ergonomically designed considering the variation in arm movement kinematics, dynamic arm biomechanics, and has been tested with different percentiles of typical pilot population.
In the preferred embodiment of the present invention, if the torque motors (102) (109) and/or the control board(115)fail to generate the active force feedback, i.e., active mode failure, the passive spring in the AFU (105) (116) provides the force feedback, thus it avoids the situation of the stick becoming light and the LVDTs(106) (113) provide the electrical voltage output proportional to the movement of the control grip (107).
The present invention provides improved comfort and legroom for the pilot with less fatigue during long flight hours. It results in significant utilization of cockpit space allowing an unobstructed path way to the emergency pilot egress.
7 Drawing numerals:

Item No. Description
101 Outer gimbal
102 Torque motor - pitch
103 Pitch motor lever
104 Force sensor assembly - pitch
105 Artificial feel unit (AFU)-pitch
106 Quadruplex pitch linear variable differential transducer (LVDT) assembly
107 Control grip
108 Inner gimbal
109 Torque motor - roll
110 Roll LVDT lever
111 Roll force sensor lever
112 Roll force sensor
113 Quadruplex roll linear variable differential transducer (LVDT) assembly
114 Modularized box assembly
115 Electronic control board
116 Artificial feel unit (AFU)-Roll
117 Lever roll
118 Roll bracket assembly
119 Roll shaft
120 Boot assembly
121 Rigging pin - pitch
122 Rigging pin - roll
123 Cover plates
124 Outlet for electrical pigtail connectors
125 Stop bolts
126 Flight control computer , C , Claims:We claim:

1. An active side control stick assembly with variable force feedback for interfacing with a flight control computer (126) of an aircraft, comprising:
- a control grip (107);
- a plurality of gimbals (101)(108);
- a plurality of torque motors (102) (109);
- a plurality of artificial feel units (105) (116);
- a plurality of quadruplex linearly variable differential transducers (LVDT)s (106) (113);
- a plurality of force sensors (104) (112);
- a plurality of levers (103) (110) (111); and
- an electronic control board (115), characterized in that, the control board(115)serves to excite the LVDTs(106) (113) and force sensors(104) (112) along with torque motors(102) (109), the board (115) receives the signals from the sensors (106)(113)(104)(112) for data processing, the control board (115) provides the tactile force feedback for the pilot proportional to the movements of the grip (107) and aircraft parameters, the feedback force is varied based on the flight conditions by varying the current of the torque motors (102) (109) and controlled by the board (115), the control grip (107) is interfaced with the outer gimbal (101) that provides the longitudinal forward and aft stick displacement along the pitch axis,the outer gimbal(101) is connected to the torque motor - pitch (102) with the pitch motor lever (103) and the force sensor assembly- pitch (104), the outer gimbal(101) is connected to the artificial feel unit-pitch (AFU-P) (105) to provide passive force feel and centering, a quadruplex pitch LVDT assembly (106) is mounted on the AFU-P assembly(105) that senses the grip (107) movement and converts it to proportional electrical output, the quadruplex LVDT assembly(106)(113) provides redundant electrical signals for longitudinal and lateral flight controls such that there is no cross-coupling between the lateral and longitudinal axes and these electrical signals are interfaced with the flight control computer (126) for further processing, the inner gimbal (108) provides lateral movements of the stick for left and right displacement that controls the roll axis of the aircraft, the roll channel of the active side control stick assembly consists of the torque motor-roll (109), and the lever assemblies (110)(111) with the force sensor assembly (112) and the quadruplex roll LVDT - artificial feel unit (AFU)-Roll (113) that is mounted to sense the grip (107) left and right movement and converts it into proportional electrical output, the active side control stick assembly translates the movement of the grip (107) in forwards/aft/left/right directions to the torque motor (102) (109) movement, the force sensors (104) (112) are provided between the gimbals (104) (108) and the torque motors (102) (109) to sense the force applied by the pilot on the grip (107),the active force feedback is generated while controlling the pitch and roll attitudes or rates of the aircraft by varying the position and current supply to the torque motors (102) (109) as controlled by the signal from the control board (115), the board (115) receives the flight parameters from the flight control computer (126) and controls the back drive torque of the motors (102) (109) by controlling the input current based on an algorithm and vary the feedback force as per the actual flight dynamics of the aircraft, the movement of the control grip (107) is adjusted for the maximum displacement using a plurality of stop bolts (125) that are adjusted in both pitch and roll directions and the artificial feel units (105) (116) that provide the required damping and passive centering of the control grip (107) which in turn ensures independent longitudinal and lateral movements with no cross-axis coupling, a predetermined relation exists between the desired displacement and movement of the control member (107), the passive spring in the AFU (105) (116) provides the force feedback in the case of failure by the torque motors (102) (109) and/or the control board (115) in generating the active force feedback and thus it avoids the situation of stick becoming light and the LVDTs (106)(113) provide the electrical voltage output proportional to the movement of the control grip (107), the electronic control board (115) generates a control signal representative of the given stick movement and other flight conditions such as load factor, airspeed, pitch attitude, angle of attack, angle of sideslip, pitch rate, roll attitude, and roll rate for the control of the torque motors (102) (109), the electronic control board (115) with the help of LVDTs (106) (113), force sensors (104) (112), and torque motors (102) (109) generate different force - displacement characteristics, breakout forces, soft stops, surpass able back stops, hard stops, and feel slopes, the control board (115) manipulates the side stick dynamics such as damped natural frequency and damping as per the flight control laws and provides the angle of attack limit awareness and ‘g’ limit awareness to the pilot and has programmable features such as stick shaking and stick push functionalities where the torque motors (102)(109) push the grip (107) towards neutral position, the active side stick control assembly provides soft stops for ‘g’ limit protection and awareness to the pilot by manipulating the current signal to the torque motors (102) (109) through the control board (115), and thereby the active side control stick assembly provides situational awareness to the pilots in an aircraft equipped with fly-by-wire type flight control system.
2. The active side control stick assembly with variable force feedback, as claimed in claim 1, wherein, the electronic control board(115) generates differential feedback forces in the roll axis based on the arm kinematics and ergonomics, where the feedback force towards the left roll is made slightly more than the right for the case of right-hand side located stick assembly, and the control board (115) generates the feedback forces of different slope curves that is force versus displacement curves with parameters that include breakout force, soft stop, and hard stop.
3. The active side control stick assembly with variable force feedback, as claimed in claim 1, wherein, the active side control stick assembly operates in a passive mode in the case of failure of active elements in the board (115) or the torque motors (102)(109), such that the AFU of pitch (105) and the AFU of roll (116) are providing the artificial feel to the pilot that provides the pilot a linearly increasing force feedback following the stick movement and the pitch and roll quadruplex LVDT assemblies(106)(113) are providing the stick position information to the computer (126) without any hindrance and loss of signal in the passive mode.
4. The active side control stick assembly with variable force feedback, as claimed in claim 1, wherein, the active side control stick assembly operates in a stick jamming mode if the gimbals (101) (108) get struck, such that the force sensors (104) (114)are providing the proportional electrical output to the electronic control board (115) and the computer (126), and the computer (126) uses these signals to control the aircraft.
5. The active side control stick assembly with variable force feedback, as claimed in claim 1, wherein, two active side control sticks are arranged in a dual-cockpit mode of a twin-seater trainer aircraft where the control board (115) duplicates the movements of the other stick based on the movements of the stick being operated by the pilot that is providing a method for automatically varying the biasing force on the grip(107) for proper pitch and roll control.
6. The active side control stick assembly with variable force feedback, as claimed in claim 1, wherein, the active side control stick assembly is ergonomically designed considering the variation in arm movement kinematics, dynamic arm biomechanics, and is tested with different percentiles of typical pilot population.
7. The active side control stick assembly with variable force feedback, as claimed in claim 1, wherein, a rotary variable differential transducer (RVDT) assembly is considered as an alternative to the LVDT assembly (106) (113).