US-20260126302-A1 - Thrust Monitoring in a Linear Drive for Independent Cart System

US20260126302A1US 20260126302 A1US20260126302 A1US 20260126302A1US-20260126302-A1

Abstract

A level of thrust generated in a linear drive system is monitored by receiving an analog feedback signal at a controller from a position sensor mounted along a track for the linear drive system. The analog feedback signal varies as a function of a position of a mover traveling along the track, and the controller receives the analog feedback signal as the mover travels between a first position and a second position proximate the position sensor. An amplitude of the analog feedback signal corresponds to a value of thrust generated by the linear drive system for the mover. A change in the analog feedback signal from a nominal value of the analog feedback signal for the mover is detected as the mover travels between the first and second positions. Operation of the linear drive system is adapted when the change in the analog feedback signal exceeds a predefined threshold.

Inventors

Yuhong Huang

Assignees

ROCKWELL AUTOMATION TECHNOLOGIES, INC.

Dates

Publication Date: 20260507
Application Date: 20251219

Claims (20)

1 . A method for monitoring an air gap in an independent cart system, comprising the steps of: receiving an analog feedback signal at a controller from a magnetic field sensor mounted along a track for the independent cart system, wherein the analog feedback signal varies in amplitude as a magnetic drive member, mounted on a mover for the independent cart system, travels past the magnetic field sensor; sampling a plurality of values of the analog feedback signal with the controller as the mover travels past the magnetic field sensor; determining an air gap between a surface of the track and a lower surface of the mover as a function of the plurality of values of the analog feedback signal sampled by the controller; and adapting operation of the mover responsive to the air gap being less than a predefined threshold.
2 . The method of claim 1 further comprising the steps of: detecting a peak value from the plurality of values of the analog feedback signal; and determining a difference between the peak value and a nominal expected peak value stored in memory of the controller, wherein the air gap is determined as a function of the difference.
3 . The method of claim 2 wherein determining the air gap further comprises the step of reading a value of the air gap from a look up table stored in the memory, wherein the value of the air gap corresponds to the difference between the peak value and the nominal expected peak value.
4 . The method of claim 2 , wherein the step of adapting operation of the linear drive system responsive to the air gap being less than the predefined threshold further comprises entering a safe torque off operating mode with the controller for the linear drive system.
5 . The method of claim 2 , wherein the step of adapting operation of the linear drive system responsive to the air gap being less than the predefined threshold further comprises generating a maintenance required message.
6 . The method of claim 2 , wherein the step of adapting operation of the linear drive system responsive to the air gap being less than the predefined threshold further comprises dynamically changing at least one value of a controller gain for the linear drive system as the mover is travelling along the track.
7 . The method of claim 2 , wherein the mover travels along the track for the independent cart system and wherein the track includes a plurality of magnetic field sensors, the method determines the air gap between the surface of the track and the lower surface of the mover at each of the plurality of magnetic field sensors.
8 . The method of claim 1 , wherein: each of the plurality of values of the analog feedback signal corresponds to a different position of the mover; the method further comprises the step of determining an area under a curve defined by the plurality of values of the analog feedback signal with respect to the different position of the mover, wherein the air gap is determined as a function of the area under the curve.
9 . A method for preventing touchdown of a mover to a track in an independent cart system, comprising the steps of: receiving an analog feedback signal at a controller from a magnetic field sensor mounted along the track, wherein the analog feedback signal varies in amplitude as a function of a position of the mover along the track; sampling a plurality of values of the analog feedback signal with the controller as the mover travels past the magnetic field sensor, wherein a waveform of the analog feedback signal is defined by the plurality of values of the analog feedback signal with respect to the position of the mover when each value is sampled; detecting a change in the analog feedback signal from a nominal value of the waveform stored in memory of the controller; determining an air gap between a surface of the track and a lower surface of the mover as a function of the change in the analog feedback signal; and adapting operation of the mover responsive to the air gap being less than a predefined threshold.
10 . The method of claim 9 , wherein the nominal value is a nominal peak value of the analog signal.
11 . The method of claim 9 , wherein the nominal value is a nominal area under the waveform of the analog feedback signal.
12 . The method of claim 9 , wherein the step of adapting operation of the mover responsive to the air gap being less than the predefined threshold further comprises entering a safe torque off operating mode with the controller.
13 . The method of claim 9 , wherein the step of adapting operation of the mover responsive to the air gap being less than the predefined threshold further comprises generating a maintenance required message.
14 . A system for monitoring an air gap in an independent cart system, comprising a track including a plurality of drive coils for a linear drive system; a mover including a drive member for the linear drive system, wherein the drive member on the mover causes the mover to travel along the track responsive to a series of electromagnetic fields generated by each of the plurality of drive coils; at least one position sensor mounted along the track, wherein the at least one position sensor is operative to generate an analog feedback signal as the mover travels past the at least one position sensor; a controller configured to: receive the analog feedback signal from the at least one position sensor, sample a plurality of values of the analog feedback signal as the mover travels past the at least one position sensor, determine an air gap between a surface of the track and a lower surface of the mover as a function of the plurality of values of the analog feedback signal sampled by the controller; and adapt operation of the mover responsive to the air gap being less than a predefined threshold.
15 . The system of claim 14 , wherein the controller is further configured to: detect a peak value from the plurality of values of the analog feedback signal; and determine a difference between the peak value and a nominal expected peak value stored in memory of the controller, wherein the air gap is determined as a function of the difference.
16 . The system of claim 15 , wherein the controller is further configured to read a value of the air gap from a look up table stored in the memory, wherein the value of the air gap corresponds to the difference between the peak value and the nominal expected peak value.
17 . The system of claim 14 , wherein: the system includes a plurality of position sensors; and the controller is further operative to determine the air gap between the surface of the track and the lower surface of the mover at each of the plurality of position sensors.
18 . The system of claim 14 , wherein the controller is further operative to adapt operation of the linear drive system responsive to the air gap being less than the predefined threshold by entering a safe torque off operating mode.
19 . The system of claim 14 , wherein the controller is further operative to adapt operation of the linear drive system responsive to the air gap being less than the predefined threshold by generating a maintenance required message.
20 . The system of claim 14 , wherein the controller is further operative to determine an area under a curve defined by the plurality of values of the analog feedback signal with respect to the position of the mover, wherein the air gap is determined as a function of the area under the curve.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation of and claims priority to U.S. application Ser. No. 18/152,888, filed Jan. 11, 2023 and titled Thrust Monitoring in a Linear Drive for Independent Cart System, the entire contents of which is incorporated herein by reference. BACKGROUND INFORMATION The subject matter disclosed herein relates to monitoring a level of thrust generated in a linear drive for an independent cart system. More specifically, systems and methods for detecting a level of thrust as a function of a position of a mover along a track segment and as a function of an air gap between the mover and the track segment are disclosed. Motion control systems utilizing movers and linear drives in an independent cart system can be used in a wide variety of processes (e.g. packaging, manufacturing, and machining) and can provide an advantage over conventional conveyor belt systems with enhanced flexibility, extremely high-speed movement, and mechanical simplicity. The motion control system includes a set of independently controlled carts, or “movers,” each supported on a track for motion along the track. The track is made up of a number of track segments that, in turn, hold individually controllable electric, drive coils. Successive activation of the drive coils establishes a moving electromagnetic field that interacts with a drive member on the movers and causes the mover to travel along the track. The drive member may be, for example, an array of permanent magnets mounted along a length of the mover. Each of the movers may be independently moved and positioned along the track in response to the moving electromagnetic field generated by the drive coils. In a typical system, the track forms a closed path over which each mover repeatedly travels. At certain positions along the track other actuators may interact with each mover. For example, the mover may be stopped at a loading station at which a first actuator places a product on the mover. The mover may then be moved along a process segment of the track where various other actuators may fill, machine, position, or otherwise interact with the product on the mover. The mover may be programmed to stop at various locations or to move at a controlled speed past each of the other actuators. After the various processes are performed, the mover may pass or stop at an unloading station at which the product is removed from the mover. The mover then completes a cycle along the closed path by returning to the loading station to receive another unit of the product. In some applications, the independent cart system may include many meters of track, extending along a process line, between a storage area and an assembly area within a facility, or other such applications. In order to reduce the cost of the system, it may be desirable to not provide drive coils for the linear drive system along the entire length of the track. Because the drive coils generate the electromagnetic filed used to propel the movers along the track, gaps between coils should be less than a width of a drive member mounted to the mover. If a gap between coils is less than the length of the magnet array, at least a portion of the drive member will always overlap one of the coils for the linear drive system. However, if only a portion of the magnet array is positioned such that it interacts with an electromagnetic filed generated by the drive coils of the linear drive system, the amount of thrust that may be generated by the linear drive system is reduced when compared to operation of the mover with the entire magnet array positioned above the drive coils. This reduced interaction between the drive coils and the magnet array may result in speed fluctuations as a mover travels across a gap or potential stalling of a mover if it stops on a gap and does not have sufficient thrust to resume motion. Thus, it would be desirable to provide a system and method for monitoring the amount of thrust available in the linear drive system as a function of the position of the mover along the track. It would also be desirable to provide a system and method to increase the amount of thrust available if needed when a mover is positioned over a gap between drive coils. It is also known that a level of thrust generated in a linear drive system is a function of an air gap between the drive coils and the drive member mounted on the mover. Over time, wear on wheels, glides, or other contacting surfaces between the track and the mover may change width of the air gap between the drive coils and the drive member. In particular, the width is typically reduced as the contacting members wear and the drive member on the mover becomes closer to the drive coils. The reduced width of the air gap causes an increased interaction of the electromagnetic field generated by the drive coils with drive member. The increased interaction causes an increased amount of thrust generated by the linear drive system th