Strapping device

Abstract

A strapping device (100) for strapping one or more articles with a strap is described, comprising a tensioning apparatus (1) for tensioning the strap around the one or more articles, a joining apparatus (2) for joining two overlapping portions of the strap and an actuating unit (3), the actuating unit (3) comprising a cam shaft (31) with a position-encoding cam or a position-encoding notch (313), and a proximity sensor (32) arranged in proximity to the position-encoding cam or the position-encoding notch (313) and configured to detect the position-encoding cam or the position-encoding notch (313), a motor (33) operatively coupled with the cam shaft (31) and configured to drive the cam shaft (31), and a rotary encoder, wherein the strapping device (100) comprises a controller (4) connected with the actuating unit (3) and configured to receive from the rotary encoder a rotor position of the motor (33) and to determine a zero-position of the cam shaft (31) using the position-encoding cam or the position-encoding notch (313).

Description

Field of the invention

[0001] The present invention relates to a strapping device for strapping one or more articles with a strap and a method of operating a strapping device.Background of the invention

[0002] Strapping devices are used for packing various articles by placing a strap around the articles such that two portions of the strap overlap each other by forming a loop around the articles. The overlapping portions of the strap are connected to each other by a strapping device which is applied to tension the strap and to join the overlapping portions of the strap. For tensioning the strap, a tensioning apparatus with a tensioning wheel is used which can be lowered onto the strap in order to contact the strap for tensioning and raised from the strap in order to release or to introduce the strap.

[0003] Various joining techniques can be used for joining the overlapping portions, such as for example welding, crimping, gluing etc., the specific technique depending on the articles to be strapped and / or the material of the strap. For joining the overlapping portions of the strap, a welding crimper can be lowered onto the strap in order to join the overlapping portions of the strap and raised from the strap in order to release or to introduce the strap.

[0004] When operating a strapping device, various components such as for example the tensioning wheel of a tensioning apparatus or a welding jaw of a welding crimper are typically actuated by a suitable actuating unit driven by a motor. The components are often actuated over considerable distances, for example when a tensioning wheel is raised and / or lowered before inserting and / or removing of a strap portion.Summary of the invention

[0005] While packing articles using a strapping device, it is desired that the actuation of the components of a strapping device is executed with a sufficient degree of spatial precision while keeping the control of the components efficient.

[0006] It is therefore an object of the invention to provide a strapping device which at least partially improves the prior art and avoids at least part of the disadvantages of the prior art.

[0007] According to the present invention, this object is achieved by the features of the independent claims. In addition, further advantageous embodiments follow from the dependent claims and the description as well as the figures.

[0008] According to an aspect of the invention, this object is particularly achieved by a strapping device for strapping one or more articles with a strap, comprising a tensioning apparatus for tensioning the strap around the one or more articles, a joining apparatus for joining two overlapping portions of the strap and an actuating unit, the actuating unit comprising a cam shaft with a position-encoding cam or a position-encoding notch, a proximity sensor arranged in proximity to the position-encoding cam or the position-encoding notch and configured to detect the position-encoding cam or the position-encoding notch, a motor operatively coupled with the cam shaft and configured to drive the cam shaft, and a rotary encoder, wherein the strapping device comprises a controller connected with the actuating unit and configured to receive from the rotary encoder a rotor position of the motor and to determine a zero-position of the cam shaft using the position-encoding cam or the position-encoding notch.

[0009] Preferably, the proximity sensor is a contactless sensor configured to detect the features of the position-encoding cam or the position-encoding notch such as the leading edge and the trailing edge without touching the position-encoding cam or the position-encoding notch. The proximity sensor may comprise one or more of: an inductive sensor, a capacitive sensor, optical sensor, magnetic sensor, ultrasonic sensor, etc.

[0010] The actuating unit may be connected to one or more components of the strapping device and configured to actuate the one or more components of the strapping device such as for example a tensioning wheel of the tensioning apparatus, a joining jaw, heating blade and / or joining plunger of the joining apparatus and / or one or more clamps of the strapping device.

[0011] Using the rotary encoder connected to the motor, the rotor position of the motor and / or changes in the rotor position of the motor, respectively, can be monitored. The motor may be an electric motor.

[0012] In some embodiments, the strapping device comprises a servo drive comprising the motor, the rotary encoder and a servo controller. The motor may thus be a servomotor.

[0013] Compared to an actuation unit without a rotary encoder or a servomotor where dedicated position sensors are required for each specific angular position of the cam shaft in order to allow for a sufficient precision on determining the cam shaft position, the number of position sensors can be reduced due to the rotary encoder or the servomotor and the controller enabling to determine the zero-position of the cam shaft using the position-encoding cam or the position-encoding notch.

[0014] The controller may comprise a central control unit such as a high-level controller and one or more ancillary control units configured to control different components of the strapping device. One of the ancillary control units may for example be dedicated to controlling the motor. The controller may for example comprise a central control unit such as a PLC (programmable logic controller) and a servo controller of a servo drive having the servo controller and a servomotor. The central control unit may for example control the position of the cam shaft by outputting a requested position of the cam shaft, wherein the servo controller may receive a signal of the central control unit for the requested position of the cam shaft and accordingly control the servomotor such that the cam shaft may be driven to the requested position of the cam shaft.

[0015] In some embodiments, the proximity sensor is configured to detect a leading edge and a trailing edge of the position-encoding cam or the position-encoding notch and to output a leading signal and a trailing signal upon detecting the leading edge and the trailing edge of the position-encoding cam or the position-encoding notch, wherein the controller is configured to receive the leading signal and the trailing signal from the proximity sensor and to determine a zero-position of the cam shaft at an angular position of the cam shaft centered between the leading edge and the trailing edge of the position-encoding cam or the position-encoding notch.

[0016] By detecting the leading edge and the trailing edge of a position-encoding cam or a position-encoding notch and determining the zero position of the cam shaft as a center angular position between the leading edge and the trailing edge of the position-encoding cam or the position-encoding notch, the precision of the zero-position used by the actuating unit can be improved.

[0017] The precision can, in particular, be improved compared to a configuration where only a single feature of a position-encoding cam or a position-encoding notch is detected by a sensor for determining a certain position of the cam shaft. By detecting two features of the position-encoding cam or the position-encoding notch such as the leading edge and the trailing edge and determining therewith a position of the cam shaft by the controller, measurement inaccuracies originating for example from the distance between the proximity sensor and the position-encoding cam or the position-encoding notch, or from the spatial extent of the respective feature of the position-encoding cam or the position-encoding notch, can be averaged out. Furthermore, a manual adjustment of the proximity sensor (or the position of the proximity sensor, respectively) and / or manual adjustment of the position-encoding cam or the position-encoding notch can be avoided, since the controller can electronically control the adjustment of the zero-position of the cam shaft. Therefore, time and effort in the installation and / or maintenance of the strapping device can be reduced.

[0018] Components actuated by the actuating unit can therefore be actuated in a more precise manner since the precision with which the cam shaft can be initiated in a reference position can be improved, thereby improving the performance of the strapping device.

[0019] In some embodiments, the controller is configured to determine the angular position of the cam shaft using a gear transmission ratio between the motor and the cam shaft.

[0020] Using the rotor position or the angular position of the rotor of the motor, respectively, and the gear transmission ratio between the motor and the cam shaft, the controller can determine the angular position of the cam shaft. Since the rotary encoder allows to continuously monitor the rotor position, the controller can monitor the angular position of the cam shaft at any desired point in time. Using the zero-position of the cam shaft, as determined by the controller as a reference position, the controller can furthermore determine the absolute angular position of the cam shaft. The precision of the control on the actuation unit and the operation of the strapping device can therefore be improved. A gear reduction ratio from the motor to the cam shaft can further improve the precision of the determination of the angular position of the cam shaft.

[0021] In some embodiments, the cam shaft comprises a single position-encoding cam or a single position-encoding notch.

[0022] Since the rotary encoder allows the controller to continuously monitor the angular position of the cam shaft and the controller can precisely determine a zero-position of the cam shaft using a position-encoding cam or a position-encoding notch of the cam shaft, separate position-encoding cams or position-encoding notches for determining a specific cam shaft position can be avoided. Therefore, the cam shaft can be simplified to comprise a single position-encoding cam or a single position-encoding notch while ensuring precise control on the angular position determination of the cam shaft. Furthermore, a single proximity sensor for detecting the single position-encoding cam or single position-encoding notch can be sufficient. Manual adjustment of additional proximity sensors and / or manual adjustment of additional position-encoding cams or position-encoding notches can therefore be avoided.

[0023] Based on the zero-position determined using the leading edge and trailing edge of the single position-encoding cam or position-encoding notch, the angular position of the cam shaft can continuously be determined by the controller using the rotor position as output by the rotary encoder and the known gear transmission ratio between the motor and the cam shaft.

[0024] In some embodiments, the single position-encoding cam or single position-encoding notch is formed on a position-encoding cam disc of the cam shaft, on a rod of the cam shaft or on a rotary cam of the cam shaft.

[0025] The single position-encoding cam or single position-encoding notch may therefore be formed on a separate single position-encoding cam disc, or directly on the rotatable rod of the cam shaft or on a rotary cam of the cam shaft used for actuation.

[0026] Compared to cam shafts with a plurality of position-encoding cams or notches, the structure of the cam shaft can therefore be simplified.

[0027] In some embodiments, the rotary encoder is a rotary incremental encoder connected with the motor and configured to output a change of a rotor position of the motor.

[0028] With the zero-position of the cam shaft, as determined by the controller using the leading edge and the trailing edge of the position-encoding cam or position-encoding notch, and the incremental position change of the rotor position, as output by the rotary incremental encoder, the controller can efficiently determine the absolute angular position of the cam shaft in a precise fashion.

[0029] In some embodiments, the actuating unit comprises a rotary absolute encoder connected with the motor and configured to output a rotor position of the motor.

[0030] In some embodiments, the controller is configured to receive an actuation command comprising a target angular position of the cam shaft, to generate a rotation signal using the actuation command and the gear transmission ratio between the motor and the cam shaft, and to transmit the rotation signal to the motor.

[0031] The controller can therefore not only be used to precisely determine the angular position of the cam shaft, but also to control the position of the cam shaft in order to precisely move the cam shaft to a desired position. The rotary encoder and the controller therefore provide the advantage of a precise position feedback mechanism by which the operation of the cam shaft can be controlled in an efficient manner. Compared to an actuation of the cam shaft using a plurality of position-encoding cams or notches which only allow for a small number of fixed and discrete angular positions to be attained, the controller with the rotary encoder improves on the flexibility on the control of the cam shaft since the desired angular position of the cam shaft can be input to the controller without the possible angular positions being restricted by the structure of the cam shaft, e.g. by the number or positions of position-encoding cams or notches of the cam shaft.

[0032] In some embodiments, the controller is configured to receive an actuation command comprising a target angular position of the cam shaft, wherein the target angular position is continuously variable over the circumference of the cam shaft.

[0033] Since the position feedback with the rotary encoder allows for the controller to continuously change the angular position of the cam shaft, the actuation command can comprise a target angular position which may cover virtually every angle over the circumference of the cam shaft. The range and / or variety of positions coverable by the components actuated by the actuating unit comprising the cam shaft can therefore significantly be increased.

[0034] In some embodiments, the controller is configured to control the motor to decelerate the cam shaft before reaching the target angular position of the cam shaft.

[0035] By decelerating the cam shaft before reaching the target angular position of the cam shaft, the components actuated by the actuating unit can be moved in a smoother fashion.

[0036] Since the actuation command received by the controller comprises the target angular position before said position is reached by the cam shaft, the controller may anticipate the reaching of the target angular position by the cam shaft.

[0037] Compared to a strapping device where the reaching of a target angular position is recognized upon detecting of a specific position-encoding cam or notch dedicated to the target angular position, the controller can therefore adapt the motion of the cam shaft while approaching the target angular position. The possibility of decelerating the cam shaft before reaching the target angular position therefore represents a further aspect of the controller of the present strapping device allowing to adapt the cam shaft motion in a more flexible fashion.

[0038] Since the rotary encoder and the controller allow to continuously monitor the angular position of the cam shaft, the cam shaft velocity can be increased for angles far off the target angular position and if required, decelerated when approaching the target angular position. By increasing the cam shaft velocity, the cycle time of a strapping process with the strapping device can be reduced.

[0039] In some embodiments, the strapping device comprises a user interface comprising one or more user input buttons for initiating one or more actuation commands.

[0040] The user interface may comprise a control panel comprising one or more user input buttons by which the controller can be accessed by a user. The user input buttons may comprise for example physical push buttons and / or input fields on a display. The display may comprise a touch screen.

[0041] In some embodiments, the controller is configured to receive at least two actuation commands each comprising a target angular position of the cam shaft, wherein at least two target angular positions of the at least two actuation commands differ by an angle which is smaller than the angular dimension of the position-encoding cam or the position-encoding notch.

[0042] The strapping device therefore allows to reduce the minimum distance between consecutively approachable target angular positions. In strapping devices where the target angular positions are defined by dedicated position-encoding cams or notches, the minimum distance between consecutive target angular positions may be limited by the angular dimensions of the respective position-encoding cams or notches, or, in order to circumvent such limitations, one may be required to introduce axially separate position-encoding cam discs. Since the controller and the rotary encoder allow for continuous monitoring and controlling of the cam shaft, consecutive target angular positions can continuously follow each other, and complex configurations of separate position-encoding cams or notches can be avoided.

[0043] In some embodiments, the strapping device comprises a strap conveying apparatus comprising one or more transport rollers for conveying the strap, the strap conveying apparatus comprising an encoder roller configured to contact the strap and a roller rotary encoder configured to monitor the encoder roller and to output an encoder signal, wherein the strapping device comprises a controller connected with the roller rotary encoder and configured to receive the encoder signal of the roller rotary encoder, to determine a speed of rotation of the encoder roller using the encoder signal of the roller rotary encoder, and to compare the speed of rotation of the encoder roller to a speed of rotation of the one or more transport rollers.

[0044] In some embodiments, the controller is configured to adapt the speed of rotation of the one or more transport rollers if a difference between the speed of rotation of the encoder roller and the speed of rotation of the one or more transport rollers exceeds a predetermined slippage velocity value.

[0045] In some embodiments, the strapping device comprises a pressure sensor or a force sensor connected with at least one transport roller and configured to detect a contact pressure or contact force of the at least one transport roller onto the strap, wherein the controller is configured to read out the pressure sensor or force sensor and to output the contact pressure or contact force if a difference between the speed of rotation of the encoder roller and the speed of rotation of the one or more transport rollers exceeds a predetermined slippage velocity value.

[0046] In some embodiments, the strapping device comprises a pressing actuator, for example a pneumatic cylinder, configured to generate a contact force or contact pressure of the one or more transport rollers onto the strap.

[0047] In some embodiments, the controller is configured to determine a strap consumption using the encoder signal of the rotary encoder.

[0048] In some embodiments, the strapping device comprises a servomotor configured to drive the one or more transport rollers.

[0049] According to a further aspect, the present invention is also directed to a strapping device for strapping one or more articles with a strap, comprising a tensioning apparatus for tensioning the strap around the one or more articles, a joining apparatus for joining two overlapping portions of the strap, and a strap conveying apparatus comprising one or more transport rollers for conveying the strap, the strap conveying apparatus comprising an encoder roller configured to contact the strap and a roller rotary encoder configured to monitor the encoder roller and to output an encoder signal, wherein the strapping device comprises a controller connected with the roller rotary encoder and configured to receive the encoder signal of the roller rotary encoder, to determine a speed of rotation of the encoder roller using the encoder signal of the roller rotary encoder, and to compare the speed of rotation of the encoder roller to a speed of rotation of the one or more transport rollers.

[0050] The encoder roller and the roller rotary encoder provide the advantage that the motion of the strap and, in particular, the actual strap velocity that corresponds to the speed of rotation of the encoder roller can be monitored. The actual strap velocity can be compared to the target strap velocity that corresponds to the speed of rotation of the one or more transport rollers being driven by a motor of the strapping device.

[0051] The strap conveying apparatus therefore allows to monitor to which extent the drive for the strap as generated by the one or more transport rollers is effectively imparted onto the strap. A discrepancy between the target strap velocity and the actual strap velocity may indicate a slippage which can be detected by the controller.

[0052] Preferably, the roller rotary encoder is a rotary incremental encoder configured to output incremental position changes of the encoder roller.

[0053] Continuously monitoring the conveyance of the strap using the encoder roller and the roller rotary encoder allows to early recognize disturbances in conveyance of the strap and thereby to prevent failures.

[0054] In some embodiments, the controller is configured to adapt the speed of rotation of the one or more transport rollers if a difference between the speed of rotation of the encoder roller and the speed of rotation of the one or more transport rollers exceeds a predetermined slippage velocity value.

[0055] By adapting the speed of rotation of the one or more transport rollers, a slippage which exceeds a predetermined tolerance value, as defined by the slippage velocity value, can be reduced. In particular, the driving of the one or more transport rollers by a motor of the strapping device can be adapted until the speed of rotation of the one or more transport rollers and the speed of rotation of the encoder roller are again in line with each other. In other words, the driving of the one or more transport rollers can be adapted such that the target strap velocity and the actual strap velocity are brought in line with each other.

[0056] The strapping device therefore allows to provide a feedback mechanism by which the slippage can be kept within a tolerable range, as defined by the predetermined slippage velocity value.

[0057] By setting a small slippage velocity value, the strapping device can be operated in a nearly slip-free fashion. Due to the feedback mechanism keeping the slippage small, the strap can be conveyed at higher velocities.

[0058] In some embodiments, the strapping device comprises a pressure sensor or a force sensor connected with at least one transport roller and configured to detect a contact pressure or contact force of the at least one transport roller onto the strap, wherein the controller is configured to read out the pressure sensor or force sensor and to output the contact pressure or contact force if a difference between the speed of rotation of the encoder roller and the speed of rotation of the one or more transport rollers exceeds a predetermined slippage velocity value.

[0059] By detecting and outputting the contact pressure or contact force of the at least one transport roller if the slippage exceeds a predetermined tolerance value, as defined by the slippage velocity value, an inaccurately adjusted contact pressure or contact force can be recognized and adapted in order to reduce the slippage. The contact pressure or contact force may be indicated on a user interface comprising a display.

[0060] In some embodiments, the strapping device comprises a pressing actuator, for example a pneumatic cylinder, configured to generate a contact force or contact pressure of the one or more transport rollers onto the strap.

[0061] The pressing actuator may therefore actuate at least one of the one or more transport rollers in order to generate and / or change a contact force or contact pressure of the one or more transport rollers onto the strap.

[0062] The controller may be configured to control the pressing actuator using the contact pressure or contact force detected by the pressure sensor or force sensor.

[0063] The controller can therefore be used to provide a contact pressure or contact force feedback mechanism where the contact pressure or contact force can be controlled using the pressure sensor or force sensor and the pressing actuator depending on the slippage.

[0064] In some embodiments, the controller is configured to determine a strap consumption using the encoder signal of the rotary encoder.

[0065] The controller may therefore count the number of revolutions of the encoder roller and determine the strap consumption therefrom.

[0066] In some embodiments, the strapping device comprises a servomotor configured to drive the one or more transport rollers.

[0067] Using the servomotor, the speed of rotation of the one or more transport rollers can be determined. The controller may be connected with the servomotor and receive the speed of rotation of the one or more transport rollers from the servomotor. The servomotor may be connected to a rotary incremental encoder connected with the controller.

[0068] According to a further aspect, the present invention is also directed to a method of operating a strapping device according to the present disclosure, comprising the steps of: Detecting the position-encoding cam or the position-encoding notch by the proximity sensor; detecting by the rotary encoder connected to the motor and the controller a rotor position of the motor; receiving by the controller from the rotary encoder a rotor position of the motor; determining by the controller a zero-position of the cam shaft using the position-encoding cam or the position-encoding notch.

[0069] In some embodiments, the proximity sensor detects a leading edge and a trailing edge of the position-encoding cam or the position-encoding notch and outputs a leading signal and a trailing signal upon detecting the leading edge and the trailing edge of the position-encoding cam or the position-encoding notch, wherein the controller receives the leading signal and the trailing signal from the proximity sensor and determines a zero-position of the cam shaft at an angular position of the cam shaft centered between the leading edge and the trailing edge of the position-encoding cam or the position-encoding notch.

[0070] A first angular position of the cam shaft or the rotor of the motor at which the leading signal is output by the proximity sensor may be determined by the respective rotor position of the motor as provided by the rotary encoder.

[0071] A second angular position of the cam shaft or the rotor of the motor at which the trailing signal is output by the proximity sensor may be determined by the respective rotor position of the motor as provided by the rotary encoder.

[0072] In some embodiments, the controller determines the angular position of the cam shaft using a gear transmission ratio between the servomotor and the cam shaft.

[0073] In some embodiments, the controller receives an actuation command comprising a target angular position of the cam shaft, generates a rotation signal using the actuation command and the gear transmission ratio between the motor and the cam shaft, and transmits the rotation signal to the motor.

[0074] In some embodiments, the controller controls the servomotor to decelerate the cam shaft before reaching the target angular position of the cam shaft.

[0075] In some embodiments, the controller receives at least two actuation commands each comprising a target angular position of the cam shaft, wherein at least two target angular positions of the at least two actuation commands differ by an angle which is smaller than the angular dimension of the position-encoding cam or the position-encoding notch.

[0076] According to a further aspect, the invention is also directed to a method of operating a strapping device according to the present disclosure, comprising the steps of: Conveying a strap by one or more transport rollers; monitoring the encoder roller by the roller rotary encoder; outputting by the roller rotary encoder an encoder signal; receiving by the controller the encoder signal of the roller rotary encoder; determining by the controller a speed of rotation of the encoder roller; comparing by the controller the speed of rotation of the encoder roller to a speed of rotation of the one or more transport rollers.

[0077] The speed of rotation of the one or more transport rollers may be monitored using a transport rotary encoder. In some embodiments, the speed of rotation of the one or more transport rollers may be monitored using a rotary encoder of a servo drive.

[0078] In some embodiments, the controller adapts the speed of rotation of the one or more transport rollers if a difference between the speed of rotation of the encoder roller and the speed of rotation of the one or more transport rollers exceeds a predetermined slippage velocity value.

[0079] In some embodiments, a pressure sensor or force sensor detects a contact pressure or contact force of the at least one transport roller onto the strap, wherein the controller reads out the pressure sensor or force sensor and outputs the contact pressure or contact force if a difference between the speed of rotation of the encoder roller and the speed of rotation of the one or more transport rollers exceeds a predetermined slippage velocity value.

[0080] In some embodiments, the controller determines a strap consumption using the encoder signal of the rotary encoder.

[0081] In some embodiments, a pressing actuator actuates at least one of the one or more transport rollers in order to generate and / or change a contact force or contact pressure of the one or more transport rollers onto the strap.

[0082] In some embodiments, the controller controls the pressing actuator using the contact pressure or contact force detected by the pressure sensor or force sensor.List of Figures

[0083] The present invention will be explained in more detail, by way of exemplary embodiments, with reference to the schematic drawing, in which: Fig.1shows a perspective view of a portion of an embodiment of a strapping device; Fig.2shows a magnified view of a part of the strapping device of Figure 1; Fig. 3shows a further magnified view of the strapping device of Figure 2 in the region of the cam shaft; Fig.4shows a flow diagram of an embodiment of a method of operating a strapping device; Fig.5shows a part of an embodiment of a strapping device in the region of the strap conveying apparatus. Detailed description of exemplary embodiments

[0084] Figure 1 shows perspective view of a portion of an embodiment of a strapping device 100 comprising a tensioning apparatus 1, a joining apparatus 2 and an actuating unit 3. The actuating unit 3 comprises a cam shaft 31, a proximity sensor 32 and a servo drive 330 with a servomotor 33. The servo drive 330 comprises the servomotor 33, a servo controller and a rotary encoder configured to monitor the rotor position of the servomotor 33. The cam shaft 31 comprises a position-encoding notch (not visible in Figure 1). The proximity sensor 32 is arranged in proximity to the position-encoding notch and configured to detect the position-encoding notch. The servomotor 33 is operatively coupled with the cam shaft 31 and configured to drive the cam shaft 31. The strapping device 100 further comprises a controller 4 connected with the actuating unit 3. The controller 4 is configured to receive from the rotary encoder of the servo drive 330 a rotor position of the servomotor 33 and to determine a zero-position of the cam shaft 31 using the detection signal of the proximity sensor 32 detecting the position-encoding notch.

[0085] Figure 2 shows a magnified view of a part of the strapping device 100 of Figure 1 in the region of the cam shaft 31. The cam shaft 31 comprises a rotatable rod 311 which is driven by the servomotor 33 shown in Figure 1 and rotary cams 312, 312' mounted on the rod 311 of the cam shaft 31. Using the rotary cams 312, 312', components of the strapping device 100 such as for example the tensioning wheel of the tensioning apparatus and / or components of the joining apparatus can be actuated. The frontmost rotary cam 312 comprises an axially protruding stub 3121 in which a position-encoding notch 313 is formed. The proximity sensor 32 is arranged in proximity to the stub 3121 and the position-encoding notch 313. When the cam shaft 31 is rotated, the stub 3121 rotates with the rod 311 until the position-encoding notch 313 passes the detection area of the proximity sensor 32 and is detected by the proximity sensor 32. The position of the cam shaft 31 where the proximity sensor 32 detects the position-encoding notch 313 is determined by the controller as the zero-position of the cam shaft 31 based on the respective rotor position of the servomotor.

[0086] Figure 3 shows a further magnified view of the strapping device 100 of Figure 2 in the region of the cam shaft 31. The position-encoding notch 313 comprises a leading edge 3131 and a trailing edge 3132 which is detected by the proximity sensor 32. In the shown embodiment, the proximity sensor 32 is an inductive sensor. The proximity sensor 32 outputs a leading signal upon detecting the leading edge 3131 and a trailing signal upon detecting the trailing edge 3132. The controller receives the leading signal and the trailing signal from the proximity sensor 32 and determines a zero-position of the cam shaft at an angular position of the cam shaft 31 centered between the leading edge 3131 and the trailing edge 3132 of the position-encoding notch 313. In the embodiment as shown in Figure 3, the zero-position of the cam shaft 31 is therefore at an angular position of the cam shaft 31 where the position-encoding notch 313 matches the horizontal level of the proximity sensor 32, as indicated by the dashed line.

[0087] Figure 4 shows a flow diagram of an embodiment of a method of operating a strapping device according to the present disclosure, for example the strapping device as shown in Figure 1-3. The proximity sensor detects the leading edge of the position-encoding notch and outputs a leading signal at an angular position x1. The angular position x1 can be determined by the respective rotor position of the servomotor as provided by the rotary encoder of the servo drive. Accordingly, the proximity sensor detects the trailing edge of the position-encoding notch and outputs a trailing signal at an angular position x2 determined by the respective rotor position of the servomotor, as provided by the rotary encoder of the servo drive. Using the angular positions x1 and x2, the controller determines the zero-position of the cam shaft by determining the angular position C0=(x1+x2) / 2 centered between the leading edge and the trailing edge of the position-encoding notch. The respective rotor position for the angular position C0 can be used to identify the zero-position of the cam shaft.

[0088] While operating the cam shaft, the rotor position PR of the servomotor can continuously be monitored by the rotary encoder and output to the controller. The controller can then determine the actual position CP of the cam shaft by using the rotor position PR as received from the rotary encoder and the zero-position of the cam shaft by means of the relation CP=C0 + (PR x R), with R the gear transmission ratio between the servomotor and the cam shaft from the gearing of the strapping device transmitting the drive from the servomotor to the cam shaft.

[0089] Similar to identifying the cam shaft position at any desired point during operation, the controller controls the position of the cam shaft upon receiving an actuation command comprising a target angular position CP' of the cam shaft. The controller then generates a rotation signal using the target angular position CP' and transmits the rotation signal to the servomotor (or the servo controller, respectively) such that the servomotor can take the rotor position PR'=(CP'-C0) / R, with R the gear transmission ratio.

[0090] Figure 5 shows a part of an embodiment of a strapping device 100' comprising a strap conveying apparatus 5 with two transport rollers 51, 52. Either one of the transport rollers 51, 52 may be driven by a motor. The strapping device 100' may have essentially the same structure as the strapping device 100 as shown in Figures 1-3. In other words, the strapping device 100 as shown in Figures 1-3 may comprise a strap conveying apparatus 5 as shown in Figure 5. The transport rollers 51, 52 are configured to convey a strap. The strap conveying apparatus 5 comprises an encoder roller 53 and a roller rotary encoder 54 configured to monitor the encoder roller 53 and to output an encoder signal. The encoder roller 53 comprises four position-encoding notches 531 and position-encoding cams 532 which can be detected by the roller rotary encoder 54. The roller rotary encoder 54 comprises an inductive proximity sensor by which the position-encoding notches 531 and / or position-encoding cams 532 are detected upon passing the roller rotary encoder 54. A controller 4 is connected with the roller rotary encoder 54 and receives the encoder signal of the roller rotary encoder 54. Using the encoder signal, the controller 4 determines the speed of rotation of the encoder roller 53. The controller is furthermore connected to the servomotor driving the transport rollers 51, 52 and therefore monitors the speed of rotation of the transport rollers 51, 52. By comparing the speed of rotation of the encoder roller 53 and the speed of rotation of the transport rollers 51, 52, the controller 4 can detect the occurrence of a slippage. In case a slippage occurs, the controller 4 can control the servomotor driving the transport rollers 51, 52 in order to adapt the speed of rotation of the transport rollers 51, 52 until the slippage is eliminated.

Claims

1. A strapping device (100, 100') for strapping one or more articles with a strap, comprising a tensioning apparatus (1) for tensioning the strap around the one or more articles, a joining apparatus (2) for joining two overlapping portions of the strap and an actuating unit (3), the actuating unit (3) comprising a cam shaft (31) with a position-encoding cam or a position-encoding notch (313), a proximity sensor (32) arranged in proximity to the position-encoding cam or the position-encoding notch (313) and configured to detect the position-encoding cam or the position-encoding notch (313), a motor (33) operatively coupled with the cam shaft (31) and configured to drive the cam shaft (31), and a rotary encoder, wherein the strapping device (100, 100') comprises a controller (4) connected with the actuating unit (3) and configured to receive from the rotary encoder a rotor position of the motor (33) and to determine a zero-position of the cam shaft (31) using the position-encoding cam or the position-encoding notch (313).

2. The strapping device (100, 100') according to claim 1, wherein the proximity sensor (32) is configured to detect a leading edge (3131) and a trailing edge (3132) of the position-encoding cam or the position-encoding notch (313) and to output a leading signal and a trailing signal upon detecting the leading edge (3131) and the trailing edge (3132) of the position-encoding cam or the position-encoding notch (313), wherein the controller (4) is configured to receive the leading signal and the trailing signal from the proximity sensor (32) and to determine a zero-position of the cam shaft (31) at an angular position of the cam shaft (31) centered between the leading edge (3131) and the trailing edge (3132) of the position-encoding cam or the position-encoding notch (313).

3. The strapping device (100, 100') according to claim 1 or 2, wherein the controller (4) is configured to determine the angular position of the cam shaft (31) using a gear transmission ratio between the motor (33) and the cam shaft (31).

4. The strapping device (100, 100') according to claim 3, wherein the controller (4) is configured to receive an actuation command comprising a target angular position of the cam shaft (31), to generate a rotation signal using the actuation command and the gear transmission ratio between the motor (33) and the cam shaft (31), and to transmit the rotation signal to the motor (33), wherein the target angular position is preferably continuously variable over the circumference of the cam shaft (31).

5. The strapping device (100, 100') according to claim 4, wherein the controller (4) is configured to control the motor (33) to decelerate the cam shaft (31) before reaching the target angular position of the cam shaft (31) .

6. The strapping device (100, 100') according to claim 4 or 5, comprising a user interface comprising one or more user input buttons for initiating one or more actuation commands.

7. The strapping device (100, 100') according to one of the claims 4 to 6, wherein the controller (4) is configured to receive at least two actuation commands each comprising a target angular position of the cam shaft (31), wherein at least two target angular positions of the at least two actuation commands differ by an angle which is smaller than the angular dimension of the position-encoding cam or the position-encoding notch (313).

8. The strapping device (100, 100') according to one of the preceding claims, wherein the cam shaft (31) comprises a single position-encoding cam or a single position-encoding notch (313), wherein the single position-encoding cam or single position-encoding notch (313) is preferably formed on a position-encoding cam disc of the cam shaft, on a rod (311) of the cam shaft or on a rotary cam (312, 312') of the cam shaft (31).

9. The strapping device (100, 100') according to one of the preceding claims, wherein the rotary encoder is a rotary incremental encoder connected with the motor (33) and configured to output a change of a rotor position of the motor (33).

10. The strapping device according to one of the preceding claims, comprising a servo drive comprising the motor, the rotary encoder and a servo controller.

11. A strapping device (100, 100') for strapping one or more articles with a strap, comprising a tensioning apparatus (1) for tensioning the strap around the one or more articles, a joining apparatus (2) for joining two overlapping portions of the strap, and a strap conveying apparatus (5) comprising one or more transport rollers (51, 52) for conveying the strap, the strap conveying apparatus (5) comprising an encoder roller (53) configured to contact the strap and a roller rotary encoder (54) configured to monitor the encoder roller (53) and to output an encoder signal, wherein the strapping device (100, 100') comprises a controller (4) connected with the roller rotary encoder (54) and configured to receive the encoder signal of the roller rotary encoder (54), to determine a speed of rotation of the encoder roller (53) using the encoder signal of the roller rotary encoder (54), and to compare the speed of rotation of the encoder roller (53) to a speed of rotation of the one or more transport rollers (51, 52).

12. The strapping device (100, 100') according to claim 11, wherein the controller (4) is configured to adapt the speed of rotation of the one or more transport rollers (51, 52) if a difference between the speed of rotation of the encoder roller (53) and the speed of rotation of the one or more transport rollers (51, 52) exceeds a predetermined slippage velocity value.

13. The strapping device according to claim 11 or 12, comprising a pressure sensor or force sensor connected with at least one transport roller and configured to detect a contact pressure or contact force of the at least one transport roller onto the strap, wherein the controller is configured to read out the pressure sensor or force sensor and to output the contact pressure or contact force if a difference between the speed of rotation of the encoder roller and the speed of rotation of the one or more transport rollers exceeds a predetermined slippage velocity value.

14. The strapping device according to one of the claims 11 to 13, wherein the controller is configured to determine a strap consumption using the encoder signal of the rotary encoder.

15. The strapping device (100, 100') according to one of the claims 11 to 14, comprising a servomotor (33) configured to drive the one or more transport rollers (51, 52).

Images