Abstract:
A cargo power drive unit includes a motor and at least one driver roller element coupled to the motor. The power drive unit further includes a light transmitter for emitting light and a light receiver for measuring light. The power drive unit measures an amount of ambient light and then measures an amount of total light after the light transmitter emits light. The power drive unit then determines whether a cargo container is present based on a calculation of reflected light and the measurement of ambient light.

Description:
FIELD OF THE INVENTION 
   One embodiment of the present invention is directed to a power drive unit for transporting cargo on an aircraft. More particularly, one embodiment of the present invention is directed to a sensor for a power drive unit for detecting unit load devices and scrubbing. 
   BACKGROUND INFORMATION 
   A large variety of motorized systems for moving cargo are known. Motor driven rollers are typically employed in these systems. Cargo and passenger airplanes in particular often employ a series of motor driven power drive units (“PDU”s) to quickly and efficiently propel cargo containers and pallets, otherwise known as unit load devices (“ULD”s), within the aircraft cargo compartment. This configuration can allow for the transportation of cargo from the external loader to the interior of the airplane by one or more operators controlling the PDUs. 
   Cargo within an airplane cargo deck is typically supported by a system of freely rotating floor-mounted conveyance rollers. Sets or banks of PDUs can be simultaneously elevated from beneath the cargo deck to a level just above the conveyance rollers. Each PDU may be a separate electromechanical actuator which includes one or more rubber coated wheels or drive rollers. The drive rollers of the elevated PDUs contact and move cargo above the conveyance rollers in the commanded direction upon energization. The movement of cargo depends on the coefficient of friction between the PDU drive rollers and the bottom surface of the cargo, as well as the lifting force generated by the PDU lift mechanism. When the PDUs are deenergized, roller rotation ceases and the cargo stops moving. 
   Several sets of PDUs can be arranged along a common path of conveyance, and each set can be operated separately, thereby allowing for the transfer of multiple pieces of cargo. An operator supervising the transportation of cargo into the cargo deck area can guide cargo by means of a joystick and an on/off switch or similar controls. 
   PDUs can be damaged when they continue to operate beneath immobilized cargo, a condition known as scrubbing, which can occur when cargo is too heavy or has come upon an obstruction such as a wall guide within the cargo compartment. Scrubbing can quickly wear away the rubber coating on the rollers necessitating their replacement and can result in damage to the PDU motor. 
   Cargo container stall sensors integrated within a PDU are used to sense a stalled container and to remove power to the PDU motor after a predetermined delay to avoid PDU damage. Some PDU control systems have a manual de-select switch for removing power to the PDUs when a stall condition is determined. Unfortunately, this de-select switch is often not used properly by operators, who are focused on loading cargo rather than protecting PDUs. Thus, damage to PDUs when scrubbing conditions occur is a common problem. 
   Known stall sensors include mechanisms for monitoring the temperature of the PDU motor, which is subject to measurement error, or require additional electro-mechanical mechanisms on the PDU, which are susceptible to wear and other maintenance issues. 
   Further, in the aircraft cargo area, it is important to keep track of the location of the ULDs. The most common method of keeping track of these ULDs, while they are in the cargo area, is by detecting them as they pass over a ULD sensor which is located on the floor of the cargo compartment. One known sensing method is the use of infrared light to determine the presence of the ULD. This known ULD detector employs a digital sensor which only allows two states (i.e., “ULD present” or “ULD not present”). Further, the circuitry used in the known detector to create and detect the infrared light requires heavy filtering because of ambient infrared light, which can vary greatly. In addition, the known ULD sensor applies power to the infrared light source constantly, which means that the amount of electrical current applied must be kept low so that the light source does not overheat. 
   Based on the foregoing, there is a need for an improved PDU that includes an integrated ULD detector and a non-mechanical scrubbing sensor. 
   SUMMARY OF THE INVENTION 
   One embodiment of the present invention is a cargo power drive unit that includes a motor and at least one driver roller element coupled to the motor. The power drive unit further includes a light transmitter for emitting light and a light receiver for measuring light. The power drive unit measures an amount of ambient light and then measures an amount of total light after the light transmitter emits light. The power drive unit then determines whether a cargo container is present based on a calculation of reflected light, the measurement of total light, and the measurement of ambient light. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates an aircraft and  FIG. 2  an aircraft cargo deck that can be used to implement an embodiment of the present invention. 
       FIG. 3  is a top view of a PDU in accordance with one embodiment of the present invention. 
       FIG. 4  is an end view of the PDU in accordance with one embodiment of the present invention. 
       FIG. 5  is a block diagram of the electronics of the PDU in accordance with one embodiment of the present invention. 
       FIG. 6  is a flow diagram of the functionality performed by the PDU in order to sense the presence of a ULD in accordance with one embodiment of the present invention. 
       FIG. 7  is a flow diagram of the functionality performed by the PDU in order to sense ULD scrubbing in accordance with one embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   One embodiment of the present invention is a PDU with an integrated sensor for detecting the presence of a ULD and for sensing scrubbing. 
     FIG. 1  illustrates an aircraft  25  and  FIG. 2  an aircraft cargo deck  26  that can be used to implement an embodiment of the present invention. A generally H-shaped conveyance surface  26  forms a deck of an aircraft, adjacent a cargo bay loading door  23 . However, there are many other aircraft cargo deck configurations to which the embodiments of the invention can be implemented. For example, some aircraft, particularly those configured primarily for the transportation of cargo without passengers, have the upper passenger deck removed and an additional larger cargo deck installed. Other aircraft may have three or more parallel longitudinal tracks rather than the H-shape shown in  FIG. 2 . 
   The cargo surface includes a system of freely rotating conveyance rollers  27  mounted in the cargo deck to define the conveyance plane. Cargo loaded onto the aircraft cargo deck can be moved manually throughout the cargo bay upon the freely rotating conveyance rollers. However, it is desirable to electro-mechanically propel the loads with minimal or no manual assistance. To this end, the H-shaped cargo surface includes a number of PDUs  28 , that provide a mechanism upon which cargo is propelled over the conveyance rollers  27 . Each PDU  28  typically includes a drive roller element which can be raised from a lowered position beneath the cargo deck to an elevated position. These PDUs are referred to as “self-lift” PDUs. In the elevated position, the drive roller element contacts and drives the overlying cargo that rides on the conveyance rollers. Other types of PDUs, which can also be used as embodiments of the present invention, are above the conveyor plane all of the time and held up by a spring. These PDUs are referred to as “spring-lift” PDUs. 
   In the longitudinal direction, the H-shaped conveyance surface  26  includes a left track and a right track along which cargo is to be stowed in parallel columns during flight. In the transverse direction, the cargo deck is also separated into a tail (or “aft”) section  11  and a forward section  12 . Thus, the left and right tracks are divided into four sections, two forward sections  13  and  15  and two aft sections  17  and  19 . In addition to the four sections, there is an additional path  21  between both tracks at the cargo door  23 . This additional path  21  divides the cargo bay between the forward and aft sections  11  and  12 . This path is used to move cargo into and out of the aircraft, and also to transfer cargo between the left and right storage tracks. 
   In one embodiment, a human operator manipulates control elements to selectively and electrically energize PDUs  28  in each of the five aforementioned sections  13 ,  15 ,  17 ,  19  and  21 . Typically, these controls are mounted in an operator interface unit. The control elements may be mounted on a wall or other structure within the cargo bay or may be portable, e.g., the controls may be in a hand held pendant. These controls will typically have an on/off switch and a joystick which, depending on the direction pushed, will energize a set of PDUs  28 , causing groups of drive roller elements to be elevated (if not already elevated) and rotated in one of two possible directions (i.e., forward or reverse). A section of PDUs will remain energized as long as the joystick is held in a corresponding position. When the joystick is released, the set of PDUs selected is de-energized and the drive roller elements are returned to their retracted position below the plane of the conveyance rollers  27 , or the PDUs remain up, and brakes are applied to hold the cargo containers in place. Control systems of this type are known in the art. 
     FIG. 3  is a top view of a PDU  28  in accordance with one embodiment of the present invention. PDU  28  includes a housing  30  which incorporates a pair of wheels  51  and  52  that function as drive roller elements. Wheels  51  and  52  are coupled to a drive shaft (not shown). PDU  28  further includes necessary motor and gear assemblies (not shown) for turning and/or raising wheels  51  and  52  so that wheels  51  and  52  are positioned above the cargo deck and are able to contact the bottom of a ULD. PDU  28  further includes an electronics cavity that is separated from the rest of the PDU by a wall  53  for housing the necessary electronics (disclosed in more detail below), and includes an electrical connector  56  for coupling the electronics to a power and a control source. PDU  28  further includes an infrared light (“IR”) transmitter  57 , such as a light emitting diode (“LED”), for transmitting infrared light, and an IR receiver  58 , such as a photo transistor, for detecting the presence of infrared light. In other embodiments, other types of light besides IR can be used. 
     FIG. 4  is an end view of PDU  28  in accordance with one embodiment of the present invention, and illustrates the relationship of PDU  28  with the bottom surface  60  of a ULD that is passing over and being propelled by PDU  28 . IR transmitter  57  transmits light that bounces off the bottom surface  60  (assuming a ULD is present) and is reflected back to IR receiver  58  where it is processed by the electronics of PDU  28 . 
     FIG. 5  is a block diagram of the ULD sensor and scrub sensor electronics of PDU  28  in accordance with one embodiment of the present invention. Coupled to IR receiver  58  is an analog to digital (“A/D”) converter  70  that takes an analog input from receiver  58  and converts it to a digital value. Coupled to A/D converter  70  is a processor  72  and memory  74 . Processor  72  may be any type of general purpose processor, and memory  74  may be any type of storage device that stores instructions to be executed by processor  72 . In one embodiment, processor  72  may include A/D converter  70  and/or memory  74 . IR transmitter  57  is coupled to an output pin of processor  72 . In one embodiment, a power driver is needed between processor  72  and IR transmitter  57 . 
   In an additional embodiment, a processor adjustable variable resistor is coupled to processor  72  and receiver  58 . The variable resistor is used to set the sensitivity of A/D converter  70 , which selects the window of light that the sensor will measure (i.e., the minimum strength of light that will be detected and the greatest strength of light that can be measured before the A/D output reaches its maximum value). 
     FIG. 6  is a flow diagram of the functionality performed by PDU  28  in order to sense the presence of a ULD in accordance with one embodiment of the present invention. In one embodiment, the functionality is implemented by software stored in memory  74  and executed by processor  72 . In other embodiments, the functionality can be performed by hardware, or any combination of hardware and software. 
     101 : The process is initialized by turning off IR transmitter  57  and setting a loop counter to an initial value. 
     102 : The ambient light is measured by reading the voltage level from A/D converter  70 . 
     103 : If the voltage reading equals a predetermined maximum reading, then the ULD sensor is not covered (i.e., a ULD is not present over PDU  28 ) and the flow moves to  109  and then  111 . 
     104 : IR transmitter  57  is turned on. 
     105 : The combined ambient light and reflected light is read from A/D converter  70 . 
     106 : IR transmitter  57  is turned off. 
     107 : The reflected light is calculated by subtracting the ambient reading at  102  from the combined reading at  105 . 
     108 : A determination is made as to whether the reflected light calculated at  107  is greater than or equal to a predetermined amount that indicates that an object (most likely a ULD) is covering the sensor. If not, then the flow moves to  109  and then  111 . If yes, then an object (e.g., a ULD) is covering the sensor at  110 . 
   In one embodiment, the sensor is covered by a ULD if, because of a ULD passing over the sensor, less ambient light gets to the sensor. The sensor may be considered covered if the ULD is positioned overhead the sensor, or between the ambient light and the sensor from any other position. 
     111 : The answer from  109  or  110  (i.e., the sensor is or is not covered) is logged or stored and the loop counter is decremented. 
     112 : A determination is made as to whether the loop counter equals 0. If not, the flow returns to  102 . If yes, at  113  a decision is made as to whether a ULD is present based on the majority of the logged decisions or some other algorithm. 
   As disclosed above, with the ULD sensor in accordance with an embodiment of the present invention, the output of the IR receiver  58  is fed directly into an A/D converter of a microprocessor instead of conditioning the signal to give only two states as in the prior art. Therefore, the reflected light can be measured as not just two levels, but many levels (e.g., 256, 1024, 4096, etc). A differential A/D converter can be used to offer increased accuracy by reducing the effects of ambient electrical noise. In addition, because the processor in the present invention takes an ambient light reading before it turns on its IR light source, the processor can subtract out the ambient light value. The present invention thus has a better sensitivity/resolution and an improved accuracy over the prior art. Because of the power/speed of the processor of the present invention, the light level may be read many times per second which also allows the processor to recognize the on/off pattern of the light from the IR LED. Further, the ULD sensor in accordance with an embodiment of the present invention turns the LED on and off which gives it a chance to cool when it is off. This allows the LED to be driven with higher current levels when it is on, thereby allowing it to emit much higher levels of light. This allows a single LED to be used in embodiments of the present invention in place of the multiple LEDs that are required to be used in prior art designs. 
     FIG. 7  is a flow diagram of the functionality performed by PDU  28  in order to sense ULD scrubbing in accordance with one embodiment of the present invention. In one embodiment, the functionality is implemented by software stored in memory  74  and executed by processor  72 . In other embodiments, the functionality can be performed by hardware, or any combination of hardware and software. 
     200 : The process is initialized by receiving as input whether the sensor is covered by a ULD (from the output of the flow illustrated in  FIG. 6 ), and whether the PDU motor is running (from other software in memory  74  that controls the PDU motor). 
     202 : If the sensor is not covered, no scrubbing can be occurring at  206  so a software timer (if running) is stopped and cleared, and the scrubbing status is cleared. 
     204 : The sensor is covered so it is determined if the PDU motor is running (i.e., the PDU wheels are being powered). If not, no scrubbing can be occurring and flow goes to  206 . 
     208 : If the scrub timer is not already running, the scrub timer is started at  210 . The scrub timer trips a software interrupt when it reaches a predetermined value. The value is based on tracking how long the PDU is running versus how long the ULD has been present over the PDU. The value put into the timer is calculated based on the container size and the speed the PDUs move the ULDs. If the timer runs out before the PDU is shutoff (i.e. “running” becomes false) or the PDU no longer has a container above it (i.e. “covered” becomes false) then the PDU tires are determined to be slipping/scrubbing. This PDU covered time versus PDU run time provides the necessary data for the PDU to function as a scrub sensor. For example, if a 50 inch container covers the ULD sensor for longer than it should (with allowances) when the PDU under the container is trying to move the container, then the container/ULD is probably stuck/scrubbing and the PDU motor should be shut off in order to avoid PDU tire wear and PDU motor overheating. 
   As an example of the timer value calculation in accordance to one embodiment of the invention: Assume the tires of a PDU turn at a speed which moves ULDs at 60 feet per minute or 1 foot per second. For a 5 foot long container, it would take 5 seconds to move the container across the PDU. The timer is loaded with 7 seconds, which equals the exact 5 seconds required plus 2 extra seconds to allow for an acceptable level of slippage. When a PDU is commanded to drive, it turns on its motor (so “running” is true at  204 ). When a ULD is moved onto the PDU, the ULD sensor is used to determine that the PDU is covered (so “covered” is true at  202 ). When both “running” and “covered” are true, the timer is started. If the timer alarm reaches its trigger value before the PDU is uncovered or the PDU motor is commanded to stop, then the container is determined to be stuck (i.e., it took too long for the PDU to move the container across itself and the “assumed” reason is that the PDU tires are slipping/scrubbing). The timer is stopped and loaded with 7 seconds each time either “running” or “covered” are false and the timer is not started again until both “running” and “covered” are true. 
   Embodiments of the present invention “assume” that the PDU tires are slipping/scrubbing when it takes “too long” for the ULD to cross the PDU (i.e., it takes longer than a calculated time for a ULD of a given length traveling at a given speed to move across the PDU). This is a valid assumption since it is true for an extremely high percentage of cases. Alternative reasons would include that the PDU has a mechanical problem—in which case shutting down the PDU because of the scrub “assumption” does no harm and may actually mitigate PDU damage. 
     220 : In one embodiment of the present invention, the timer interrupt feature built into many of today&#39;s processors is utilized. In this embodiment, the expiration of the scrub timer causes entry into an interrupt routine. In other embodiments, a non-interrupt software timer can be utilized, or a hardware timer, or combination of the two. 
     222 : The scrubbing status is set, and action can be taken based on the status (e.g., automatically shut off the PDU motor because of the scrubbing). This action can occur in the interrupt routine and/or in other routines in the memory  74 . 
   The internal PDU motor automatic scrub timeout shutdown can be reset each time the PDU processor receives a PDU motor off command from the system controller (e.g., when the cargo system human operator releases the joystick). This allows the cargo system human operator to once again drive the PDU motor under a scrubbing container in an attempt to free/move the container. 
   As disclosed, the PDU in accordance with the present invention uses an IR transmitter and receiver to detect the presence of a ULD over a PDU, and to detect scrubbing, without requiring the use of extra hardware such as an additional wheel. 
   Several embodiments of the present invention are specifically illustrated and/or described herein. However, it will be appreciated that modifications and variations of the present invention are covered by the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention.