Patent Application
20060071116
This disclosure relates to automatically dispensing and/or retrieving cable from a spool.
Remote controlled vehicles, such as robots used to detect and defuse landmines, often include a communications cable that connects the vehicle to a remote control device and serves as a communications link between the vehicle and a remote operator. As an operator controls the vehicle, the communications cable can become damaged if the vehicle runs over the cable or if the cable is subjected to too much tension. Risk of cable damage is particularly acute if relatively fragile communications cable such as fiber optic cable is used.
In one aspect, the invention features a method and system for automatically dispensing and retrieving cable from a spool that includes dispensing a length of cable between a release point and the ground in a generally downward direction such that at least a portion of the length of cable between the release point and the ground is permitted to move along a first axis that is parallel to the ground and controlling pay out or retrieval of the cable to maintain the portion of the length of cable located between the release point and the ground at a predetermined position along the first axis.
In one particular implementation a sensor (e.g., a flex sensor, optical sensor, etc.) is used to sense the position of the cable at one or more points between the release point and the ground. A controller controls the speed and direction of a motor coupled to a spool for storing the cable to maintain the cable in its predetermined position. The predetermined position of the cable is a position, such as the natural catenary arc formed between the release point and the ground, in which the cable experiences no tension other than tension due to the weight of the cable. The system may use parallel guide bars or other mechanisms (e.g., a V-shaped bar) that define a slot that restricts the lateral movement of a portion of the cable in directions other than along the first axis.
In another particular implementation, the system includes a traverse mechanism for synchronizing the release point of the cable such that the release point is in line with a point at which cable is supplied to or released from the spool such that the cable is stored in a level wind. The traverse mechanism may be mechanically coupled to the spool such that when the reel motor rotates the spool the traverse mechanism traverses the longitudinal axis of the spool. Alternatively, the traverse mechanism may be coupled to a traverse motor that moves the traverse assembly along an axis parallel to a longitudinal axis of the spool. The speed and direction traverse motor may be controller to synchronize the release point of the cable such that the release point is in line with a point at which cable is supplied to or released from the spool.
In another implementation, the system includes a mechanism for maintaining a constant tension on the cable in a direction perpendicular to the longitudinal axis of the spool as cable is supplied to or released from the spool. The mechanism for maintaining a constant tension may include a pinch wheel and a drive wheel coupled to a motor. Cable is fed and compressed between the pinch wheel and drive wheel and the drive wheel is coupled to a motor that operates the drive wheel motor at a constant torque. In this implementation, the system may also monitor the direction of travel of both the drive wheel motor and the reel motor (e.g., using an optical encoder) to detect a fault if a direction of travel of the drive wheel motor is opposite a direction of travel of the reel drive motor.
The system may be attached to a remote controlled vehicle and the first axis may be parallel with the forwards and reverse direction of travel of the vehicle.
In another aspect, the invention features a method that includes dispensing a length of cable between a release point and the ground in a generally downward direction such that at least a portion of the length of cable between the release point and the ground is permitted to move along a first axis that is parallel to the ground and is not permitted to move substantially along other axes parallel to the ground, sensing a position (e.g., using a flex sensor) of the cable relative to a set point located between the release point and the ground, wherein the set point is located on the first axis, and controlling pay out or retrieval of the cable to maintain the cable at the set point along the first axis.
In one particular implementation, the method also includes dispensing a length of cable from a spool of cable and storing the cable on the spool in a level wind. The method may also include providing a traverse mechanism that moves the release point along an axis parallel to a longitudinal axis of the spool such that a line defined by the release point and the point at which cable is supplied to or released from the spool is approximately perpendicular to the longitudinal axis of the spool.
In another implementation, the method further includes controlling the speed and direction of a reel motor coupled to the spool such the cable maintains its position at the set point along the first axis.
In another implementation, the method includes compressing cable between a pinch wheel and a drive wheel and operating a motor coupled to the drive wheel at a constant torque. In this implementation, the direction of the reel motor and drive wheel motor may be monitored to detect a fault if a direction of travel of the drive wheel motor is opposite a direction of travel of the reel drive motor.
In another aspect, the invention features an apparatus for dispensing and retrieving a length of cable, wherein the cable is dispensed from the apparatus at a release point to the ground in a generally downward direction that includes a flexible cable guide tube located between the release point and the ground that defines a channel having a longitudinal axis that is generally perpendicular to the ground and configured to receive a length of cable. The flexible cable guide tube is further configured to permit cable located with the channel from moving along a longitudinal axis that is generally parallel to the ground. The apparatus also includes flex sensor located adjacent to the flexible cable guide tube to detect position of at least a portion of the cable located within the channel of the flexible cable guide tube.
In one implementation, a controller is electrically coupled to the flex sensor and is configured to receive a signal from the flex sensor indicating a detected position of the cable within the guide tube and control speed and direction of cable pay out to maintain the detected position of the cable at a predetermined position.
In another implementation, the apparatus further includes a pair of rails that defines a slot through which cable is passed. The slot can be configured to constrain lateral movement of cable in directions except along the first axis. In another implementation, a scraper attached to the flexible guide tube; the scraper has an aperture slightly larger than an outer diameter of the cable and is configured to scrape dirt and debris off of the cable as it is wound onto the reel.
In another implementation, the apparatus includes a rigid cable guide tube located between the release point and the ground and above the flexible guide tube. The rigid cable guide tube defines a second channel having a longitudinal axis that is generally perpendicular to the ground and configured to receive a length of cable. The rigid cable guide tube further configured to constrain cable located with the channel from moving along a longitudinal axis that is generally parallel to the ground.
In another aspect, the invention features a method that includes dispensing a length of cable stored on a spool between a release point and the ground in a generally vertical direction, passing the length of cable between a slot defined by two sidewalls, wherein constrains lateral motion of cable located within the slot except along a longitudinal axis, and controlling speed and direction of a reel motor coupled to the spool to maintain a portion of the length cable located between the release point and the ground at a predetermined position along the longitudinal axis.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.
Referring to
The communications cable 14 serves as a communication link between the vehicle 12 and a remote control device 17 handled by the operator 16. Data representing vehicle control commands (e.g., forward, reverse, turn left, turn right, etc.) is transmitted from the remote control device 17 to the vehicle. Additionally, sensory data obtained from one or more sensors mounted on the vehicle is transmitted from the vehicle to a display and storage device such as a TV/VCR (not shown) located within the remote control device 17.
As the operator controls the vehicle 12, the cable dispensing and retrieval system 10 controls pay out and retrieval of cable allowing a high degree of freedom of movement while managing the cable to help reduce risk of damage during operation of the vehicle. This permits multiple reuse of the cable and long service life.
Referring to
In operation, the cable dispensing and retrieval system 10 monitors the position of a portion of the cable along its catenary arc and automatically dispenses or retrieves cable to maintain the shape of catenary arc A in plane P of the cable. For example, if a user moves the remote-controlled vehicle 12 forward (indicated by the forward arrow), the catenary arc of the cable will tend to widen as more cable is suspended above the ground. However, when the cable dispensing and retrieval system 10 senses a change in the shape of the catenary arc A in plane P, it will dispense cable at a rate of speed sufficient to maintain the shape of the catenary arc. Similarly, if a user moves the vehicle 12 in a reverse direction (indicated by the reverse arrow), the catenary arc of the cable will tend to narrow. When the cable dispensing and retrieval system 10 senses this change in shape of the catenary arc A in plane P, it will retrieve cable at a rate of speed sufficient to maintain the shape of catenary arc A. By controlling dispense and retrieval of the cable to ensure that the cable maintains a particular catenary arc shape between a release point and the ground, the system helps to ensure that the cable is not subject to tension or driven over while the user controls the vehicle.
In one implementation, a cable dispensing and retrieval system monitors change in position of a portion of the cable between the release point and ground along an axis parallel to the ground and controls pay out or retrieval of cable in order to maintain the monitored portion of the cable in a predetermined position. For example, as shown in
In addition to controlling pay out and retrieval of the cable so that it maintains a particular catenary arc, the cable dispensing and retrieval system also includes a traverse assembly that ensures that the cable is dispensed and retrieved at an angle of approximately 90 degrees from the longitudinal axis of the reel spool. The traverse assembly also ensures that cable is wound onto the spool in a level wind.
Referring to
The power reel assembly 24 includes a reel spool 16 and axle (not shown) that is supported by a bearing tower 34 and motor tower 36. The reel spool 16 is powered by a reel drive motor 37 housed within the motor tower 36. A slip joint (not shown) mounted on the reel motor receives one end of the reel spool axle. The reel drive motor 37 drives the reel spool 16 and axle through the slip joint. A power/communications cord 40 connects the reel drive motor 37 to the controller assembly 28 through which electrical power and motor control signals are supplied to the motor.
The bearing tower 34 includes a bearing block assembly 38 (shown in
The controller assembly 28 houses the controller (not shown) that controls operation of the reel drive motor 36, pinch drive wheel motor 62, and includes a system power switch 27, an emergency stop button 25, a manual feed switch 23 and a calibration button 21.
The traverse assembly 28 includes a mounting block 46 and a self-reversing screw 44 that is aligned with the longitudinal axis of the reel spool 16. One end of the self-reversing screw includes a pulley 43a that is mechanically coupled to a shaft 41 with a first drive belt 42 and a second drive belt (not shown) located between the reel 16 and the motor tower 36 mechanically couples the shaft 41 with the reel spool 16. In particular, the second drive belt is mechanically coupled between a pulley (not shown) on the axle of the reel 16 and a pulley (not shown) on one end of shaft 41 (i.e., the end located adjacent to the spool reel 16). The first drive belt 42 is coupled between the pulley 43a on the self-reversing screw 44 and a pulley 43b on the shaft 41. The pulleys and drive belts are arranged such that when the reel spool 16 rotates in a first direction (e.g., clockwise) the drive belts causes the self-reversing screw 44 to rotate in the first direction; and when the reel spool rotates in the opposite direction (e.g., counter-clockwise) the self-reversing screw also rotates in the opposite direction. The traverse pulley ratios are selected to wind the cable on the spool to achieve wide spacing between adjacent windings. Changing the pulley ratios varies the spacing between adjacent windings, and wide spacing provides for reliable tangle free dispensing. In one implementation, the pulley ratios are selected to produce a pseudo random homogeneous wrap distribution, which means that cable is wound such that there are a high number of reel revolutions (e.g., 10,000) before the traverse assembly retraces the same path across the reel and that the space between an adjacent winding is relatively wide.
As the self-reversing screw rotates, the mounting block traverses parallel with the longitudinal axis of the reel spool 16. The self-reversing screw 44 is threaded such that the mounting block will switch its direction of travel when it reaches an end of the screw without having the screw to change its direction of rotation. A pinch wheel assembly 22 is mounted to the mounting block 46 and thus traverses with the mounting block. A horizontal guide bar 29 supports the lower end of the pinch wheel assembly 22.
Referring to
Cable 14 is fed from the reel through the vertical cable rollers 56a-56b, between the pinch wheels 58a-58c and drive wheel 60 wrapping around the drive wheel approximately 90 degrees, through the rigid split tube cable guide 53, the flexible guide tube 50, and scraper 51, and finally between the cable guide bars 54a-54b. The pinch wheels 58a-58c and drive wheel 60 are spaced such that the cable 14 is firmly held between the pinch wheels and the drive wheel. The drive wheel 60 is mechanically coupled to a pinch drive wheel motor 62 (shown in
Each pinch wheel 58a-58c includes an adjustment screw 66a-66c that adjusts a compression spring (not shown) and moves the pinch wheel closer to or further from the drive wheel 60. An operator can adjust the pinch wheels using the adjustment screws to ensure that the pinch wheels compress the cable against the drive wheel enough for the drive wheel to maintain a tension on the cable without the cable slipping as it is dispensed or retrieved.
The pair of guide bars 54a-54b are positioned in parallel and are spaced such that they permit cable to move freely along one axis between the release point and the guide bars, but prevent the cable from substantially moving in other directions. For example, as shown in
Each flex sensor 52a, 52b is a long, flat flexible resistor that changes resistance when it is flexed. The flex sensors are attached to the guide tube 50 with, for example, adhesive or clips. The flex sensors are oriented such that their planar surface is perpendicular to the axis along which the cable is able to move. For example, as shown in
In this implementation, two flex sensors are positioned “back-to-back” and electrically connected in a series half bridge. The sensors can be connected “back-to back” by adhesive for example to provide greater signal amplitude and physical durability. By connecting the flex sensors in a series half bridge, the sensors reduce thermal effects, provide greater signal amplitude and symmetrical performance when flexed forward or backward versus a system that uses a single flex sensor. For example, referring again to
In another implementation only one flex sensor is used. The system controller calibration characterizes the feedback sensor output with amount of cable dispensed and retrieved beyond the desired set point position thereby accepting a wide range of feedback sensor behavior. With feedback sensor characterization the control system can function with a wide range of feedback sensors.
The cable scraper 51 is a small rigid plastic piece that fits onto the lower end of the flexible tube 50. The cable scraper 51 has an opening through which the cable passes. This opening is designed to be slightly larger than the outer diameter of the cable 14 and functions to scrape dirt and debris off of the cable as it is retrieved by the system 10.
Referring to
The microcontroller 102 includes a mode function 104 that controls the mode of operation of the cable dispensing and retrieval system 10. In one implementation, there are five modes of operation:
1. Calibration mode. When the system is initially powered up or if re-calibration is selected by an operator (e.g., by pressing the calibration button 21 on the control panel 28 or selecting re-calibration from a remote control device), the mode function 104 places the system 10 in a calibration mode, which causes a calibration function 106 to run. During calibration mode, the mode function 104 does not permit command data from the operator 108 (e.g., forward, reverse, left, right, etc.) to be supplied to the vehicle 110. After the calibration function is complete, the mode function 104 switches the system to the automatic mode.
2. Automatic mode. In this mode, the pay out and retrieval of cable is automatically controlled by the microcontroller based on flexure of the flex sensors. The mode function permits command data from the operator 108 to be supplied to the vehicle 110. In addition, the mode function also preferably monitors vehicle commands supplied by the operator while the system 10 is in the automatic mode to prevent commands likely to damage the communications cable from being supplied to the vehicle. For example, the mode function may prevent an operator from commanding the vehicle to turn at a turn radius (e.g., a turn radius of less than three feet) that would likely cause the vehicle to run over and potentially damage the cable.
3. Manual mode. In this mode, pay out and retrieval of cable is manually controlled by the operator through the operator's remote control device (e.g., remote control device 17 shown in
4. Off mode. In this mode, operator commands 108 are supplied to the vehicle 110 but no cable is dispensed or retrieved.
5. Forward-Retrieve mode. In this mode, the microcontroller 102 controls the reel motor 37 such that cable is retrieved as the vehicle moves forward (in the automatic mode cable is dispensed as the vehicle is moved forward). This mode can be used, for example, if the vehicle has traveled a distance in a relatively straight line and makes a 180-degree turn and begins coming back to its starting point. Rather than dispensing cable, the forward-retrieve mode allows the operator to cause the system to retrieve the dispensed cable as the vehicle returns to its starting point.
An operator may switch between the operating modes via the operator's remote control device. In addition, the operator may switch to the manual feed mode via the switch 23 provided on the control panel 28 (shown in
During calibration mode, the calibration function 106 determines a gain 116 and an offset 114 to apply to the signal produced by the flex sensors as well as the relationship between the signal received from the sensor and the cable's displacement. To do this, in one implementation, the operator first positions the cable to a desired catenary arc position. This becomes the set point. Then calibration begins by first recording the sensor output indicating the desired set point. Then the microcontroller 102 causes the reel motor to dispense and retrieve a measured length of cable such that the flex sensors are flexed at several points over their entire operating range and readings of the signal produced by the sensors at each point is recorded. The calibration function 106 takes a series of readings (e.g., every 0.1 seconds or every 0.1 inch of dispensed cable) of the signal received from the flex sensor and performs a 2nd order least squares fit to determine the relationship between the signal from the sensor and the cable's displacement. From these readings, the calibration function 106 also determines the gain 116 and offset 114 for the flex sensors. If the calibration data reveals that an adjustment of the gain or offset is necessary then the calibration function first returns the cable to the set point, then makes the gain 116 or offset 114 adjustment, and then repeats the data collection. This process is repeated until the sensor signal is determined to be sufficient to provide satisfactory performance. This least square fit is supplied to the position error function 125 then on to the PID controller 126, where it is used to determine the Pulse Width Modulated (PWM) signal that is supplied to the dead band eliminator function 128 (described below) and then the mode function 104 and then to the motor controller 132 of the reel motor 37. Because the response of the flex sensors will vary with temperature, the calibration function 106 records a reading of the ambient air temperature from a temperature sensor 118. During operation of the vehicle (e.g., in automatic, manual, stop or forward-retrieve mode), the mode function 104 will alert the user that the system needs to be recalibrated if the ambient air temperature changes from the temperature at which calibration had been performed by a certain amount (e.g., 20 degrees Fahrenheit). In another implementation, the microcontroller 106 automatically adjusts the gain 116 and offset 114 of the flex sensors to compensate for temperature or changes the 2nd order least squares fit equation by utilizing sensor characterization history information stored in the microcontroller memory. In this embodiment, the microcontroller maintains predetermined data that estimates the effect of temperature on the response of the flex sensors. Such data may be obtained through system use or experiment. As temperature changes, the microcontroller adjusts the gain, offset and set point according to the stored data.
The calibration function 106 also operates to discover the amount of drive signal necessary to provide to the reel motor before the motor starts to move in either direction, which is referred to as “dead band” current. By compensating for this “dead band” current, the controller can more precisely control the reel motor. In one implementation, when the system 10 is turned on, the microcontroller processes a calibration routine in which the microcontroller supplies a signal to the reel motor to cause it to begin to turn and records the threshold of motion signal supplied to the reel motor. This is repeated for the opposite direction and recorded. The output of the PID controller 126 is offset by the dead band eliminator function 128 using the amount of the recorded “dead band” drive signal corresponding to each direction less any dead band desired to remain thus reducing or eliminating the “dead band” behavior. Since dead band can change with conditions such as temperature this calibration can be repeated when conditions require (e.g., temperature changes by more than a predetermined amount) measuring and eliminating any amount of the “dead band” behavior desired.
The calibration function also operates to determine if the pinch wheels 58a-58c (shown in
In a preferred embodiment, the calibration function simultaneously determines the gain, offset, relationship between sensor signal and cable displacement, dead band current and pinch wheel slippage.
Once the system has been calibrated, it is ready to operate in the automatic and forward-retrieve modes. While operating in these modes, the microcontroller 102 receives signals from the flex sensors (which are converted from analog to digital form via an A-D converter 124) that indicated the displacement of the flex sensors. These signals are fed into the microcontroller's position error function 125 and then to the PID 120, which computes a control signal. The control signal is adjusted by the dead band eliminator 122 and is fed to the mode function 104 then to the PWM 122 that commands the reel motor controller 124. This will cause payout or retrieval of cable to cause the flex sensors to return to the set point position.
In this implementation, the drive wheel motor 144 is not directly controlled by the microcontroller 102, but rather is supplied with current from a current regulator 142 such that the drive wheel motor 144 maintains a constant torque that tends to pull the cable from the reel.
During operation in any of the modes in which cable is retrieved or dispensed, the microcontroller monitors the position readings of the drive wheel encoder and the reel encoder to detect faults in operation of the system. In particular, the fault detection function 134 monitors the encoder readings to ensure that both encoders are always moving in the same direction. If the fault detection function 134 detects that the encoders are traveling in opposite directions, this indicates that the cable has become stuck or snagged on the reel and rather than dispensing, for example, the reel is actually retrieving cable. If the fault detection function 134 detects that the encoders are traveling in opposite directions, the mode function 104 immediately shuts down operation of both motors by sending a signal to a relay switch 130, 146 to stop current from being supplied to the motors and produces an alarm and/or produces a stop motion command to the vehicle. Control may be resumed after switching to manual or off modes to attempt correction of the snag or end of reel condition. Similarly if the mode function 104 receives a signal from the control panel indicating that the emergency stop button has been pressed 112, the mode function immediately cuts off current to both motors and passes on the emergency stop condition to the vehicle control system.
In addition to detecting when the motors travel in opposite directions, the fault detection function 134 also monitors the ratio of drive wheel encoder revolutions to reel encoder revolutions to determine when the reel is about to run out of cable. For example, when the reel is full of cable, the ratio of drive wheel encoder revolutions to one reel encoder revolution is relatively high in comparison to when the reel is empty. When the ratio of the drive wheel encoder revolutions to reel encoder revolutions reaches a predetermined value, the mode function 104 sends an audio alert 140 to a speaker 142 to notify the operator that the vehicle is about to run out of cable.
The microcontroller 102 includes a communication protocol identifier 150 that permits the microcontroller 102 to receive commands from a remote control device using any of several different protocols. In operation, the protocol identifier analysis incoming command data and identifies the protocol by decoding the first one or several commands received using different protocols. If a command is successfully decoded using a decoding method defined by one of the supported protocols, the protocol identifier 150 assumes that the remote control device is using that protocol and begins decoding commands using the specified decoding technique. For example, military remote control systems may employ any of three protocols, one which includes an 8-bit check sum protocol, a second which includes a 16 bit cyclic redundancy check (CRC) protocol, or a third protocol called the Joint Architecture of Unmanned Ground Systems (JAUS). A protocol identifier can be configured to attempt all three decode techniques on an initial command and automatically determine which protocol is being used by seeing which decode technique resulted in a valid command. The ability of the communication protocol identifier to accept one of a number of communication protocols allows the system to be operable with all versions of an evolving product line as well as systems from varying product lines, manufacturers and military.
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, while the figures above illustrate a cable dispensing and retrieval system which is mounted to a moving vehicle, other implementations may utilize a similar cable dispensing and retrieval system in which a user (or a mechanical device) pulls cable from a stationary system. For example, a worker laying communication cable may have a cable dispensing and retrieval system mounted to the back of a work vehicle. When the worker needs to pull some cable from the reel, he or she simply begins pulling one end of the cable. As the user pulls on the cable, the system would detect a change in the position of the monitored portion of the cable and rotate the reel so that cable is dispensed from the reel without subjecting it to excessive tension.
The traverse assembly shown and described above is synchronized with the reel motor via a mechanical coupling. Other implementations may employ a more sophisticated traverse assembly in which the traverse is controlled by a separate motor. In these implementations, position of the traverse motor and position of the reel motor could be fed into a PID controller to synchronize the traverse and the reel motors.
Other implementations may employ non-parallel guide bars. For example, one implementation employs a pair of angled guide bars that form a V-shape. The cable is fed between a slot defined by the angled guide bars and a sensor (e.g., flex sensor or position sensor) senses the position of a portion of the cable between the release point and the ground along one axis parallel to the ground.
In another implementation, the guide bar and sensor are configured to rotate along the axis of the cable between the release point and the ground based on command data received from the operator. For example, if the operator commands the vehicle to turn, the guide bars and sensor could be configured to automatically rotate in the direction of the turn just prior to the vehicle making the turn. By rotating the guide bar and sensor just prior to a turn, performance of the cable dispensing and retrieval system may be enhanced. In addition, the guide bars and sensor may be configured to rotate (either automatically or at the command of an operator) 90 degrees when the system is employed on a turret of a vehicle. For example, if the cable dispensing and retrieval system is employed on the back of a turret of an excavator, the operator may drive the excavator to a desired location and then begin sending command data instructing the excavator to rotate its turret (e.g., to begin digging). When the microcontroller receives command data instructing the excavator to rotate its turret, the microcontroller may automatically rotate at least the guide bars and sensor by 90 degrees so that monitored axis (defined by the guide bars and sensor) of the cable is tangential to the radius of turret travel.
In yet other implementations, the microcontroller automatically augments the control scheme. For example, if the microcontroller receives a command signal instructing the vehicle to take a turn, the microcontroller may change the set point of the control scheme so that cable is picked up or paid out faster during the turn to avoid dragging the cable across the ground. Similarly, the microcontroller may turn the integrator of the PID controller off when the vehicle is stopped.
As mentioned above, the microcontroller uses the encoder ratios to determine a volume of cable that is on the reel. In other implementations, the microcontroller may automatically adjust the control scheme based on the volume of cable that it determines is on the reel. For example, when the reel is relatively full (thus requiring more torque to rotate the spool) the microcontroller may adjust the proportional, integrator and differential gains of the PID controller. Similarly, as cable is pulled from the reel the microcontroller may be configured to automatically gradually adjust the proportional, integrator and differential gains of the PID controller.
In another implementation, the microcontroller automatically adjusts the cable tension. For example, if the microcontroller is operating in the calibration mode and slip is detected, the pinch motor current could be temporarily adjusted to stop slippage and allow calibration to complete. Similarly the pinch motor current could be adjusted based on the reel motor acceleration and direction.
As mentioned above, tension is applied to the cable between the reel and the drive wheel pinch point. A second cable cleaner could be located in this section of cable. In one implementation it could be comprised of a wiper device that is in contact with the fiber during retrieve only and not during dispense. In another implementation it could be part of a pair vertical guide wheels (e.g., guide wheels 56a and 56b shown in
The calibration mode of a controller could use a characterization array technique instead of a 2nd order equation in another implementation. For example, the data collected during calibration could be stored in an array. Sensor signals would be interpolated from the data set stored in the calibration array.
Accordingly, other embodiments are within the scope of the following claims.
