DESCRIPTION OF THE INVENTION

[0018] Conventional PDU's are mechanically complex and lack flexibility under varying operating conditions or vehicles. The present invention addresses and solves these problems of conventional PDU's.

[0019] The PDU of the present invention includes two separate electronically controlled electric motors, one for the drive function and one for the lift function. These motors can both be permanent magnet alternating current (PMAC) motors, commonly referred to as “brushless DC” motors. The motors have their own control electronics, which are integrated into the PDU's electronics module. The dual electronically controlled motor arrangement of the present invention provides independent, fully controllable power to both the drive and lift functions of the PDU. For example, the maximum drive torque and the maximum lift force of the PDU can be set and changed independently by the control software of the PDU, thereby providing maximum flexibility for using the actuator in various cargo applications. Furthermore, unlike prior art actuators, the present invention does not retract and then lift upon change of drive direction; the drive roller stays in constant contact with the container when the drive direction is reversed, thereby avoiding unwanted cargo movement when changing drive direction. Moreover, the use of electronically controlled motors in the inventive actuator improves upon the state of the art by providing increased motive force, reduced power consumption and reduced weight compared to prior art actuators.

[0020] An embodiment of the present invention will now be described with reference to FIGS. 1 - 4 . A PDU 100 according to the present invention comprises a support base 105 of a metal such as aluminum, to which is mounted drive means, such as a drive assembly 110 pivotably mounted via pivot pins 115 for limited vertical movement substantially normal to the longitudinal axis L of support base 105 . Drive assembly 110 comprises a drive roller 120 having an elastomeric outer surface, and means for rotating roller 120 , such as an electronically controlled electric motor; e.g., a conventional PMAC motor 125 for rotating roller 120 via planetary gear assembly 130 , pinion gear 135 , idler gear 140 and output gear 145 (see FIG. 3 ).

[0021] The inventive PDU also incorporates lift means, such as lift assembly 150 , for raising the drive means from its lowered position, as by rotating cams on a common camshaft against reaction points or bearings in the support base. The lift means provides vertical force to the drive roller, which in turn provides the frictional force to drive the container. More specifically, lift assembly 150 comprises an electronically controlled electric motor such as a conventional PMAC motor 155 . As shown in FIGS. 3 and 4 , lift motor 155 transmits power through a planetary gear assembly 160 , a lift cable driver 165 , lift cables 170 and a lift pulley 175 to a cam shaft 180 which carries a pair of cams 185 at either end. Cams 185 react against bearings 190 supported by lift reaction pins 190 a in support base 105 to move drive assembly 110 relative to support base 105 around pivot pin 115 from a retracted position substantially within support base 105 (as shown in FIGS. 1 - 4 ) to an extended position wherein roller 120 is in driving abutment against the cargo (not shown). Lift motor 155 drives at approximately 11,000 rpm as drive assembly 110 is raising, and then operates in a stalled condition when drive roller 120 comes in contact with a container bottom, or when lift assembly 150 reaches its internal lift stop (not shown).

[0022] Lift assembly 150 incorporates tension cables 170 to transmit torque from lift motor 155 and gearing 160 to lift cams 185 . In prior art actuators, the common means to provide torque to lift cams is to use gearing. The layout of the present invention is designed so that drive roller 120 is located between motors 125 , 155 and lift cams 185 . This layout provides optimum load distribution and minimizes the loads transmitted into support base 105 . Torque transmission from the lift gearing 160 to cams 185 is accomplished by one or more multi-strand, steel or composite cables or straps 170 , which are pulled by driver 165 at the output of lift gearing 160 , and in turn pull cams 185 at a fixed radius. Cams 185 rotates against reaction bearings 190 in support base 105 , thereby providing both vertical motion and vertical force to drive roller 120 . Since an independent lift motor 155 is used, lift assembly 150 is designed to rotate in a single direction, regardless of the direction of drive roller rotation. The cable lift mechanism of the present invention provides a lighter weight, lower cost solution which can be operated in an open environment, eliminating the need for the prior art's sealed gearing at the output of the lift mechanism.

[0023] PDU 100 also comprises control means for independently controlling the lift means and the means for rotating the roller, such as an electronic controller 195 for electronically controlling drive motor 125 and lift motor 155 in a conventional manner as required by all electronically controlled motors, and for performing logical, memory and other operations which will be described in detail hereinbelow. Electronic controller 195 also includes built-in-test (BIT) functions to verify the proper operation of the actuator prior to use. Electronic controller 195 includes an input/output port 200 , such as a serial port, for receiving signals from an external controller (not shown) and for sending signals to the external controller or other external devices, such as a computer. Electronic controller 195 further comprises a non-volatile memory that is used to collect and retain operating information of PDU 100 , such as total operating time, total operating cycles, or any other data available to electronic controller 195 . This data can be extracted via input/output port 200 for purposes of tracking reliability data or verifying usage.

[0024] Electronic controller 195 performs several critical functions. It controls independent lift and drive motors 125 , 155 , vehicle interface and logic functions, as well as providing electromagnetic interference control. Conventional power control modules for both motors 125 , 155 are incorporated into electronic controller 195 , which in one embodiment of the present invention comprises ‘cool’ MOSFETs (metal oxide semiconductor field effect transistors) for power switching. These devices have advantageously low power dissipation, and are ideally suited to application in a PDU. Electronic controller 195 can also utilize advanced IGBTs (integrated gate bipolar transistors) for other critical switching functions. Each motor 125 , 155 can be controlled by its own microprocessor within electronic controller 195 which stores software code, including the current and force limit settings for the motors, acceleration and deceleration rates, timeouts and delays, and any other necessary information. Electronic controller 195 can also include an EMI (electro-magnetic interference) filter to limit both the conducted EMI from PDU 100 as well as the EMI susceptibility of PDU 100 to within industry standards.

[0025] PDU 100 further includes two separate non-contacting sensors 205 which detect the presence of cargo containers above PDU 100 . Sensors 205 can be one or more of several types of non-contacting sensors, e.g. infrared, ultrasonic, Hall effect, etc. The sensor cargo presence signals are received by electronic controller 195 , which operates motors 125 , 155 only if it receives the cargo presence signal from at least one of the sensors 205 . Electronic controller 195 applies ‘OR’ logic to insure that PDU 100 's motors 125 , 155 operate when one sensor 205 experiences a failure (ON or OFF). The dual sensors provide added protection from contamination that might block one sensor 205 and render PDU 100 inoperable. Alternatively, electronic controller 195 can receive a manual override signal from the external controller through input/output port 200 , and in response will operate motors 125 , 155 regardless of whether the cargo presence signal is received from sensors 205 . This manual override mode is used for system check-out and for sensor fault override.

[0026] In addition to cargo sensors 205 , temperature sensors 205 a are provided for monitoring the temperature of motors 125 , 155 and the temperature of electronic controller 195 . Electronic controller 195 also monitors motor operating parameters such as electrical current draw and speed of motors 125 , 155 in a conventional manner employing sensors incorporated into motors 125 , 155 , such as rotor position sensors, which are required for operation of motors 125 , 155 . Using sensors 205 a and its monitoring functions, electronic controller 195 provides internal self-protection against overheating, as well as protection against both drive motor and lift motor overloads. As discussed above, electronic controller 195 can provide feedback to the external controller through input/output port 200 . Such feedback signals can include but are not limited to container presence, drive motor speed, drive roller speed, drive or lift motor current or corresponding loads, thermal protection status and a PDU identifier code.

[0027] Drive and lift motors 125 , 155 and their associated gearing are designed to be installed into a center housing 210 of PDU 100 comprising a single, continuous bore. Center housing 210 contains both drive and the lift motors 125 , 155 , planetary lift gearing 160 , planetary primary drive gearing 130 , inboard bearing support 215 , outboard bearing supports 220 , 225 and end covers 230 , 235 . The advantages of this configuration are the ease of manufacture of the housing bore 210 , the ease of assembly of components into a common bore, and the elimination of shimming during assembly. Shimming is a time consuming and error prone step in the assembly process which is avoided in this embodiment of the present invention. Shimming is eliminated in the inventive apparatus, despite the numerous axial components in the bore, because inboard bearing support 215 not only supports the inboard bearings of the rotors of both drive and lift motors 125 , 155 , but also provides an axial spring 215 a which compensates for the tolerance stack-up in the bore of center housing 210 . The assembled components are compressed against spring 215 a and are retained by end covers 230 , 235 thereby eliminating gaps between all the components in the bore of center housing 210 .

[0028] Lift assembly 150 also includes a one-way clutch 240 between lift motor 155 and lift gearing 160 to eliminate the impact loads which would normally occur when drive assembly 110 retracts to the lowered position. During retraction, lift motor 155 accelerates to high speed; clutch 240 allows motor 155 to ‘free-wheel’ to a stop after lift cams 185 contact their down direction stop (not shown).

[0029] The performance and operational availability of a PDU is directly related to the size and durability of its drive roller(s). The size of the drive roller (based on its diameter and length) relative to the overall ‘footprint’ or top view of the PDU is advantageously maximized to insure good contact with the container, as well as long roller life. Drive roller 120 of PDU 100 of the present invention encompasses approximately 23% of its support base 105 's footprint (i.e., the length and width of support base 105 ), with a total surface area of approximately 48 square inches. By comparison, prior art PDUs used in air cargo have single or dual drive rollers that are about 12% to 17% of the footprint area, and total surface areas of 7 to 39 square inches.

[0030] The fixed support base of the inventive PDU 100 is designed to minimize weight and cost, yet still transfer the required loads from drive assembly 110 to the vehicle floor structure. This is accomplished by the layout and load distribution described above, which transfers the loads imparted to drive roller 120 through pivot pins 115 and lift cams 185 and into the corners of base 105 through reaction pins 190 . This minimizes bending and deflection in support base 105 , and allows base 105 to be manufactured with aluminum sheet stampings or thin-walled extrusions.

[0031] Several exemplary actuation functions or “modes” of PDU 100 will now be described. The “retracted mode” is the normal rest mode of PDU 100 , wherein external power is removed, no drive or hold command is sent from the external controller, or no container is present (i.e., no cargo presence signal is generated by sensors 205 ). Retract mode facilitates the manual movement of containers. since drive assembly 1 10 is retracted below the conveyance plane.

[0032] In the “lift and drive mode”, lift assembly 150 raises drive assembly 110 into contact with a container and drive roller 120 rotates to move the container. A direction command from the external controller and the cargo presence signal are required for this mode. Unlike typical prior art actuators having a single motor for both lifting and driving, PDU 100 does not retract and then lift upon a change of drive direction. Rather, drive roller 120 stays in constant contact with the container when the drive direction is reversed, because electronic controller 195 causes drive motor 125 to reverse direction while maintaining lift assembly 150 in the extended position.

[0033] In the “hold mode”, lift assembly 150 raises drive assembly 110 into contact with a container and drive roller 120 is restrained from rotating by drive motor 125 and its associated drive gearing 135 , 140 , 145 . The hold function of the inventive PDU 100 does not require a separate brake (e.g., a friction-type brake), because drive motor 125 is locked electronically by electronic controller 195 to prevent rotation of drive roller 120 . This mode is intended to stop and hold containers in position, and can be used continuously when power is available to PDU 100 . The hold mode is selectable via a command from the external controller such that the operator can choose to have PDU 100 hold or retract when the drive command is removed. For example, a pin of input/output port 200 can be connected to the vehicle ground as a signal to electronic controller 195 that the hold mode is desired. This can be applied without operator input, such as when a cargo door of an airplane is opened and the PDU system is turned on, all PDU's are placed in hold mode. The hold mode is typically maintained by the airplane's logic controllers when AC power is interrupted. For example, the hold mode can be engaged by a relay in the airplane.

[0034] Unlike prior art PDUs, the actuator of the present invention has the ability to resume the container holding mode after AC power is removed and subsequently re-applied without operator input. This is particularly important in the air cargo industry, where AC power is typically supplied by a ground power cart, aircraft generators, or an aircraft auxiliary power unit (APU), and is subject to momentary interruption and re-application at any time. Prior art PDUs can lose contact with and control of the cargo container upon power interruption, because they retract immediately upon power interruption and require a drive command to be reapplied by the operator upon resumption of AC power delivery to resume holding (since they typically have a common lift and drive motor). In contrast, PDU 100 of the present invention retracts upon interruption of AC power, but when power is reapplied, sensors 205 detect cargo above them, and electronic controller 195 sees the hold signal, because the hold mode was engaged by the aircraft controller prior to power interruption, as discussed immediately above. In response to the cargo presence signal and the hold signal. electronic controller 195 automatically causes lift assembly 150 to move from the retracted to the extended position and drive assembly 110 to hold the cargo in place. A drive signal from the operator is not necessary.

[0035] In a further embodiment of the present invention, PDU 100 incorporates a traction and scrubbing control function, featuring sensors and logic which limit unnecessary scrubbing of the drive roller under parked or jammed containers, thereby avoiding excessive drive roller wear and motor overheating. When a container reaches its intended position against a latch or another container, it is said to be parked. Most prior art PDUs will continue to drive against a parked container until the drive command is removed, or until the PDU overheats. Some PDUs have incorporated ‘time-outs’ or container motion sensors to limit scrubbing under parked containers. However, time-outs do not allow the operator the flexibility to work with various sizes of containers, and motion sensors may not work well under wet or slow moving containers.

[0036] Electronic controller 195 of PDU 100 of the present invention analyzes the amount of torque applied to drive roller 120 (which is proportional to drive motor 125 's current draw) and the motor 125 's run time to determine the instantaneous power consumption of drive motor 125 . More particularly, electronic controller 195 includes conventional circuitry for measuring the electrical current draw of drive motor 125 and for monitoring the measured current draw. Electronic controller 195 compares a power consumption curve stored in its memory to the monitored current draw, and shuts off drive motor 125 when its power consumption exceeds this curve. Under high traction loads, the drive time is limited to reduce drive roller scrubbing. Under lighter loads, as are encountered with lightweight or wet containers, drive motor 125 runs as long as the drive command is applied. This logic reduces the likelihood of ‘false trips’, and lets drive motor 125 run long enough to ‘squeegee’ a wet drive roller and move wet containers.

[0037] In one embodiment of the present invention, scrubbing (i.e., controlled roller wear) is accomplished by turning off drive motor 125 when the accumulated energy delivered to drive roller 120 via drive motor 125 exceeds a preset limit. The accumulated energy (E _accumulated ) is calculated by summing the total dissipated energy (E _dis ) sampled over time, Dissipated energy is energy (E _in ) that is being delivered to motor 125 in excess of a predetermined threshold energy value (E _th ). Threshold and accumulated energy are programmable into electronic controller 195 for each PDU application and are governed by the following equations:

E _in =∫P _in dt =∫( I _s ² *R _m ) dt (1)

E _th ∫P _th dt =∫( I _th ² *R _m ) dt (2)

E _dis =E _in −E _th (3)

E _accumulated =ΣE _dis dn (4)

[0038] where:

[0039] R _m =Motor resistance, normalized=1

[0040] I _s =Sampled current

[0041] P _in =Power into motor 125

[0042] I _th =Threshold value determined for each application

[0043] P _th =Threshold power.

[0044] Sample power consumption curves are depicted in FIGS. 5A and 5B . FIG. 5A shows PDU energy usage with a variable load at drive roller 120 , and FIG. 5B shows accumulated energy with a variable load at drive roller 120 .

[0045] The PDU of the present invention is designed to operate in a number of different vehicle applications, with no changes to the actuator. It can be pre-programmed to work in several applications where a different traction forces, lift forces or logic delays are required. Electronic controller 195 has sufficient memory to store multiple programs for multiple PDU applications. As discussed above, feedback signals can also be provided to an external controller. Any one of a plurality of different external controllers can be used with a single inventive PDU by using different electrical interface cables, such as cable 300 shown in FIG. 1 . The interface cables attach to input/output port 200 but have a distinct vehicle interface connector, such as connector 300 a , based on the controller application. Circuitry internal to the particular electrical interface cable, such as circuitry 300 b , identifies the cable type to electronic controller 195 via input/output port 200 , and in response electronic controller 195 selects and uses software specific to that application stored in its memory. Thus, the same PDU 100 can be installed in a different position or a different vehicle type, and work properly without any changes to the unit.

[0046] The inventive PDU features two separate permanent magnet brushless DC electric motors, one for the drive function and one for the lift function. The motors have their own control electronics, which are integrated into a PDU electronics module. The drive motor is current limited to control the maximum available drive torque, which can be varied for different cargo applications along with the maximum lift force of the PDU, via control software. The dual motor arrangement provides independent, fully controllable operation of both the drive and lift functions of the PDU of the present invention. This independence and programmability provides maximum flexibility for using the inventive PDU in various applications.

[0047] The present invention can be practiced by employing conventional materials. methodology and equipment. Accordingly, the details of such materials, equipment and methodology are not set forth herein in detail. In the previous descriptions, numerous specific details are set forth, such as specific materials, structures, chemicals, processes, etc., in order to provide a thorough understanding of the present invention. However, it should be recognized that the present invention can be practiced without resorting to the details specifically set forth. In other instances, well known processing structures have not been described in detail in order not to unnecessarily obscure the present invention.

[0048] Only the preferred embodiment of the present invention and but a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.