GB2067490A - Tracked conveyors driven by stepping motors - Google Patents

Abstract

A conveyor comprises a load bearing track supporting a mobile carrier driven by a stepping motor (23) connected to an electrical pulse generator in a control unit (27). A plurality of electrical conductors (33) extend parallel to the track and provide a power supply as well as electrical control signals for controlling operation of the carrier (12) adjacent that part of the track. <IMAGE>

Description

SPECIFICATION Improvements in or relating to conveyors The invention relates to conveyors and more particularlyto conveyors arranged to convey loads supported on a load bearing track.

Such conveyors are currently used for numerous purposes including, for example, handling heavy loads such as car engines during assembly. The handling of such loads whilst suspended from a conveyor may require considerable variation in the transport characteristics while the load is still suspended from the conveyor. It has been known to use self-propelled carriers suspended from a load bearing track and many such self-propelled carriers have been driven by electric motors. However, numerous problems have arisen. Firstly there is the problem of changing speed by more than a very limited speed ratio such as for example a 10:1 ratio. To achieve greater speed variation than this has involved considerable complexity. Further difficulties arise in enabling such self-propelled carriers to operate satisfactorily backwards as well as forwards.A further problem has arisen in controlling the rate of acceleration or deceleration on changing speed of such a carrier with a heavy load.

It is an object of the invention to provide an improved conveyor system with simple and effective variation in transport characteristics and simple control of said variation.

The present invention provides a conveyor comprising a load bearing track, a mobile load carrier mounted on said track and movable along the track, a drive unit connected to said load carrier comprising a stepping motor and an electrical pulse generator arranged to generate strain of drive pulsesofvari- able frequency for driving the stepping motor at a correspondingly variable speed, load support means mounted on said carrier so that a load may be supported on the carrier and moved along the track by operation of the stepping motor, power supply means comprising at least one electrical conductor extending along at least part of the track parallel thereto, and control signal means comprising at least one electrical conductorextending along at least part of the track and parallel thereto and arranged to provide electrical signals for controlling the operation of the load carrier while adjacent that part of the track, said drive unit being provided with means for engaging the power supply conductor and the control signal conductor and delivering the signals to a control unit movable with the carrier and operably connected to said drive unit.

The use of a stepping motor with a variable frequency source of drive pulses provides a particularly advantageous motor for such a load carrier. The motor can be arranged to provide a torque suitable for carrying a gross load up to, for example, one tonne at high speeds from 25 meters per minute down to low speeds at 25 millimeters per minute or less. The speed range can be infinitely variable and can be set locally on the load carrier or programmed remotely. The change of speed can be controlled as well as the rate of acceleration or deceleration to ensure smooth transitions during variation of transport characteristics. This is especially important when the loads hang on chains and are free to swing. Furthermore stepping motors may be truly bidirectional so that they can move backwards and forwards in exactly the same way.A typicai stepping motor may operate with 200 steps per revolution and the motor may be made to step at rates of up to 5000 steps per second. This would provide a rotational speed of 1500 r.p.m. and after gearing this can produce a forward speed as high as, for example, 25 meters per minute. There is no lower limit to the slowest speed that can be achieved. The speed range may be 1000:1 or more and this provides great fiexibility in designing 3 conveyor system intended to permit various operations on suspended loads which require considerable var. jsicn in speed of travel.

Due to the smooth transitions in speed variation less wear and tear arises on mechanical parts and the precise control of deceleration or braking allows emergency stops to be effected where necessary.

The stepping motor may be arranged to operate under constant torque conditions. Alternatively a variable torque control system may be used. The advantage of using a torque control system is that the torque may be varied (a) for safety (b) to cope with varying inclinations of the track, and (c) to maximise energy saving. Regarding safety, the maximum limit to the torque can be preset. In this way, should the torque value required from the motor exceed the maximum limit set due, for example, to meeting an obs truction,the load carrier would halt.

In order to cope with uphill sections of track the torque may be varied when the carrier is on an inclined section of track so as to suit the gradient. On uphill sections it may be desirable to slow down the pulse frequency and/or alterthe mark to space ratio of the pulses fed to the stepping rotor and thereby vary the torque. To achieve maximum energy saving, the torque control system may be arranged to provide the minimum torque necessaryforthe particular load atthe speed required. To achieve the necessary torque control the drive unit may be provided with a torque sensor. In some cases it may be desirable to alterthetorque by remote control signals fed to the drive unit through the said control signal means.

The conveyor may be arranged to operate with a wide variety of power systems as the stepping motor is not directly connected to the power supply system but is driven by pulses from the drive unit Standard power supply systems may be rectified and transformed by a switching rectifier system to provide an input to the drive unit in appropriate form which may for example be 75 volts D.C. There is however a wide tolerance on supply voltage i.e. D.C. orA.C. single phase or poly-phase iow voltage medium voltage which can be used to provide an input to the drive unit.

The control signal conductors may be connected to a central control system arranged to provide control signals to a plurality of sections of conveyor track and thereby provide centralised control of the operation of a large number of load carriers.

Preferably said load carrier comprises a trolley provided with wheels or rollers for engaging said track and preferably said drive unit a 7d control unit are mounted on said trolley.

Preferably said power supply conductor is mounted on said track and electrically insulated therefrom. Preferably control signal conductors are mounted on said track and electrically insulated therefrom. The power supply means may comprise a plurality of conductors arranged to supply a multi phase electrical supply. Preferably the electrical power and control signal conductors comprise a bus-bar system.

Said load suspension means may include one or more adjustable hoist devices. Preferably said hoist devices are operably connected to said control unit so as to be operated in response to signalsfrom said control signal conductor or conductors.

Said drive unit is preferably arranged to drive the stepper motor in either forward or reverse directions.

Preferably the control unit includes a plurality of local controls mounted on said load carrier for controlling the operation of the load carrier which may be used in place of the signals from the control signal conductors.

Means may be provided on said load carrier for selecting priority of control between the local controls and the signals from the control signal conductore.

Preferably said control unit is arranged to control the direction, andorthe speed, andior acceleration or deceleration of movement of the load carrier, andior the torque of the stepping motor.

In some instances it may be desirable to operate said conveyor in a predetermined synchronism with a second conveyor and in such a case the second conveyor is preferably provided with a second pulse generator indicating the speed of movement of the second conveyor and the output of the second pulse generator is fed to synchronising means which is arranged to feed a train of pulses to the stepping motor so that the load carrier moves with the required speed relationship to said second conveyor.

Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a side view of part of an apparatus forming a first embodiment of the invention, Figure 2 shows the first embodiment on a section at right angles to the view shown in Figure 1, Figure 3 is a view in the same direction as Figure 1 of part of a second embodiment of the invention, Figure 4 is a section through the second embodiment at right angles to the view shown in Figure 3, and Figure 5 is a block diagram showing the control system applicable to both the first and second embodiments.

The example shown in Figures 1 and 2 includes a mono-rail conveyor system having a load bearing track 11 provided by an I-shaped beam extending along the length of the conveyor path. The track 11 may extend around an assembly plant and in this example is shown for use in assembling moto-- hi- cle engines. A plurality of mobile load carriers 12 are suspended from the track although only one is shown in the drawings. Each load carrier may be used to carry one engine unit and transport the unit throughout part or all of its travel around the plant.

The track 11 may comprise part of a linear path or a looped path and may include junctions and repair bays.

Inthe example shown in Figures 1 and 2 each load carrier 12 comprises a trolley formed by a load carrying beam 13 extending horizontally between two carriages 14 and 15 at each end of the beam 13. Each of the carriages 14 and 15 comprises two side plates 16 and 17 spaced apart on opposite sides of the track 11 and joined at their lower edges so that the carriage is of substantially U-shaped construction. At the upper end of each carriage are mounted two wheels or rollers 18 mounted on an axle 19 extending between the side plates so that the wheels run on the lower flange of the track 11. The track itself is supported by projecting arms 20 secured to vertical posts 21 at intervals along the length of the track.In the example shown in Figures 1 and 2 the carriage 15 at the trailing end of the trolley 12 is not power dri- ven and is merely arranged to free-wheel along the track. The leading carriage 14 is however provided with an electrical stepping motor 23 mounted on the side plate 17 of the carriage. The motor is arranged to drive through a coupling 24to a gear box 25. The box 25 is connected by a drive chain 26 to a wheel 18. A drive unit and control unit are mounted as indicated at 27 on the side plate 17. The beam 13 supports two electrically operated hoists 28 which are connected through chain links to a suspension system 29 from which is suspended on hooks 30 and 31 a vehicle motor unit 32.

In order to operate and control the stepping motor 23 as well as the hoists 28, a bus-bar system 33 is mounted below the track 11 and extends parallel thereto although insulated from the track 11. The bus-bar system includes a number of electrical conductors feeding a multi-phase electrical power supply for driving the motor 23 and the hoists 28. It also includes a number of electrical control signal conductors extending parallel to the track 11 and arranged to provide control signals for controlling the operation of the motor and the hoists. As can be seen from Figure 2, an electrical pick-up trolley 34 is mounted between the side plates 16 and 17 7 of the carriage and is arranged to make electrical contact with the bus-bars so as to pick up the power supply and the electrical control signals. The trolley 34 is connected through a flexible linkage to the load carrier 12 so as to be moved in synchronism with the carrier along the track 11. In this way the trolley 34 provides power and control signals from a remote source adapted to control the operation of the conveyor and hoists adjacent the part of the track from which the signals have been derived. The signals are fed to the drive and control unit 27. The hoists 28 may also be coupled to the control unit 27 so as to derive operating and power signals. Preferably two trolleys 34 are provided for picking up power and control signals for each carrier 12. These are spaced apart along the length of the carrier so as to avoid problems at any junction in the bus-bar system.

Such an arrangement will be described in more detail with reference to Figure 3.

In the arrangement shown in Figures 1 and 2 a second conveyor 35 is provided at floor level and this may be used for various purposes such as the transport of other devices which are needed in synchronism with movement of the engine unit 32 during assembly. If it is desired to synchronise the speed of movement of the carrier 12 with the movement of the second conveyor 35 this can be done by means of electrical pulse signals derived from a digitiser36 coupled to the conveyor 35 and arranged to provide along line 37 a sequence of electrical pulses representing the speed of movement of the conveyor 35.

These pulses are also fed to the drive and control unit 27 on the carrier 12 so that the stepping motor 23 is then operated in synchronism with the conveyor 35. The control unit 27 in that case includes a synchronising unit.

The control unit 27 also includes a number of local controls mounted on the carrier 12 for controlling the operation of the load carrier and hoists 28 so that the local controls may be used in place of those derived from the bus-bar system 33. The control unit also includes a priority selector switch for determining whether or not the apparatus will respond to the local controls on the carrierorthe signals derived from the bus-bar system.

The control and drive unit 27 includes a variable frequency pulse generator arranged to supply a pulse train to the stepping motor 23 at a variable frequency so that the motor can be driven in either the forward or reverse directions with variable speed as well as variable acceleration or deceleration and variable maximum torque. In this example the car rier 12 may carry a gross load of upto one tonne at speeds from 25 meters per minute down to 25 millimeters per minute or less. In this particular example the power supply on the bus-bar 33 is a three- phase supply at 380/415 volts A.C. The maximum speed obtainable from the carrier may be varied in an inverse linear relationship with the load to be carried.

The arrangement of the controls is shown more fully in schematic form in Figure 5. The stepping motor 23 derives signals from a drive controller 40 and also provides a feedback signal to the controller 40. The drive controller 40 receives electrical power supply from the bus-bars 33 through a power conditioner 41 which rectifies and transforms the power supply. It can receive control signals either from the control signal conductors in the bus-bar system 33 or alternatively from the group of local controls 42.

The local controls include a speed control, acceleration control, braking control, direction of movement control and a torque control. As is shown in Figure 5 the local controls 42, powerconditioner41, drive controller 40 and stepping motor 23 are all mounted on the movable carrier 12. The alternative centralised controls consists of a group 43 similar to the group 42 but mounted at a central control console together with a signal modulator 44. The output of the modulator 44 is fed into the bus-bar system 33.

By use of the central control system linked to each carrierthroughthe control signal conductors of the bus-bar system 33 it is possible to control a large number of carriers 12 on the same conveyor system.

In this case it may be desirable to provide a plurality of coded signals along the bus-bar system 33 so that each carrier 12 detects only those signals which are appropriately coded for that carrier 12. If desired each carrier 12 may be provided with means for feeding a signal into the control bus-bars 33 so as to indicate to the central control console the position of the carrier and to provide an alarm signal calling for help should there be any failure in operation of the carrier.

A second embodiment of the invention is shown in Figures 3 and 4. These figures show only part of the system and it is generally similar to that already described with reference to Figures 1,2 and 5 with the exception of the following features. In this case the power supply conductors and control signal conductors forming the bus-bar system 33 are mounted on one side of the vertical web of the track 11 rather than below the track 11. The carrier 12 has again two carriages 14 and 15 at each end one of which is power driven and both are guided laterally in relation to the lower flange of the track 11 by a number of rollers 45 arranged to rotate about the vertical axes. The beam 13 supports the control and drive unit 27 which is electrically coupled to the stepping motor as well as the hoists 28.The carriages 14 and 15 are pivotally mounted at each end of the beam 13 so asto enable movement of the carrier 12 around a curved track. The carriages 14 and 15 have respective projections 13a and 13b as buffer and safety means. As is clearly shown in Figure 3, two collector trolleys 34 are arranged to slide in contact with the bus-bars 33 at spaced intervals along their length. The two collector trolleys 34 are connected by flexible linkages 46 to the carriages 14 and 15. The collector trolleys 34 are also electrically connected to the control unit 27. As can be seen from Figure 4, each collector trolley 34 is arranged to move along the track 11 in synchronism with the carrier 12 with the collectortrolley 34 sliding in a channel shaped casing 47 so that the collector trolley 34 is in electrical contact with the bus-bars.In this way the bus-bar system and collector trolleys are protected from accidental damage by being located within the flanges of the I-beam forming the track.

Furthermore, in the examples shown in Figures 3 and 4 the stepping motor 23 is connected through a mounting unit 48 to the coupling 25 which in this case is arranged to rotate two pinions 49 forming part of a geartrain including gear rings 50 coupled to the carriage wheels 18. The electrical power supply and control signals from a central console 51 are fed in through a conductor 52 at a position unrelated to the location of the carrier.

The arrangement shown in Figures 3 and 4 also includes local controls on the carrier which may be selected to take priority over the remote controls.

It will be appreciated that in all the above exam ples the carriers can be arranged to convey heavy loads in the forwards or backwards direction with considerable variation in speed whilst maintaining smooth transition from one speed to another together with controiled acceieration or decelera- tion. Furthermore the operation of te carriers and/or hoists can be controlled from ne remote central console or from local controls on each carrier.

Claims (10)

1. A conveyor comprising a load bearing track, a mobile load carrier mounted on said track and mov- able along the track, a mobile load carrier mounted on said track and movable along the track, a drive unit connected to said load carrier, load support means mounted on said carrier so that a load may be supported on the carrier and moved along the track by operation of the drive unit, characterised in that the drive means comprises a stepping motor and an electrical pulse generator arranged to generate a train of drive pulses of variable frequency for driving the stepping motor at a correspondingly variable speed, power supply means comprising at least one electrical conductor extends along at least part of the track parallel thereto, and control signal means comprising at least one electrical conductor extends along at least part of the track and parallel thereto and is arranged to provide electrical signals for controlling the operation of the load carrier while adjacent that part of the track, said drive unit being provided with means for engaging the power supply conductor and the control signal conductor and delivering the signals to a control unit movable with the carrier and operably connected to said drive unit.

2. A conveyor according to claim 1 further characterised in that the control signal conductors are connected to a central control system arranged to provide control signals to a plurality of sections of conveyor track and thereby provide centralised control of the operation of a number of load carriers.

3. A conveyor according to claim 1 or claim 2 further characterised in that said load carrier comprises a trolley provided with wheels or rollers for engaging said track and said drive and control unit are mounted on said trolley.

4. A conveyor according to any one of the preceding claims further characterised in that said power supply conductor and said control signal conductors are mounted on said track and electrically insulated therefrom.

5. A conveyor according to any one of claims 1 to 4 further characterised in that said load suspension means includes one or more adjustable hoist devices operably connected to said control unit so as to be operated in response to signalsfrom said control signal conductor or conductors.

6. A conveyor according to any one of the preceding claims further characterised in that the con trol unit includes a plurality of local controls mounted on said load carrier for controlling the operation of the load carrier which may be used in place of the signals from the control signal conductors.

7. A conveyor according to claim 6 further characterised by means on said load carrier for selecting priority of control between the local con trols and the signals from the control signal conduc tors.

8. A conveyor according to anyone of the pre ceding claims in which said control unit is arranged to control the direction, and/or the speed, andfr acceleration or deceleration of movement of the load carrier, and/orthetorque of the stepping motor.

9. A conveyor according to any one of the preceding claims further characterised by a second conveyor is provided with a second pulse generator indicating the speed of movement of the second conveyor and the outpExt of the second pulse generator is fed to synchronising means which is arranged to feed a train of pulses to the stepping motor so that the load carrier moves with the required speed relationship to said second conveyor.

New claims or amendments to claims filed on 21 st April 1981.

New claim

10. A conveyor substantially as hereinbefore described with reference to Figures 1 and 2 or Figures 3 and 4 or Figure 5 of the accompanying drawings.