CONTAINER SEALING UNIT

The invention relates to a container sealing unit for sealing plastics covers to containers. Known container sealing units comprise a support carrying a plurality of sealing heads and associated temperature sensors for monitoring the temperature of the sealing heads. The unit is mounted in sealing apparatus which typically includes a conveyor system for conveying open containers such as trays underneath the container sealing unit. The sealing heads of the unit are then brought towards the container with a plastics film in between so as to heat and then seal the film as a cover onto the container. Examples of known tray sealing apparatus are described in EP-A-1468913 and EP-A-0680880.

In order to control accurately the sealing operation, each sealing head and each temperature sensor is connected to a remote control unit. The remote control unit can then monitor the temperature of each sealing head and control the supply of power to heat the sealing head accordingly. This is a complex arrangement in view of the amount of electrical wiring required.

In accordance with the present invention, a container sealing unit comprises a support carrying a plurality of sealing heads for heat sealing a plastics cover to a container, and a corresponding plurality of temperature sensors for monitoring the temperature of each sealing head; a communications interface unit mounted to the support and adapted to be connected by a communications channel to a remote control unit, whereby communication between the sealing heads and temperature sensors and the remote control unit is via the communications unit and communications channel; and a power connector mounted to the support and having a single input for connection to a remote power supply and outputs connected to the sealing heads. With the present invention, we arrange for all communications with the remote control unit to be channelled through the communications interface unit and thus avoid the need for complex electrical wiring, all individual connections with the sealing heads and temperature sensors being made through the

communications interface unit and thus these can be permanent. In addition, the invention utilizes a power connector to enable a single connection to be made with a remote power supply, the power connector then distributing power to the or each sealing head. Thus, with this invention, the number of external connections that have to be made to the sealing unit is significantly reduced in comparison with conventional sealing units, typically to a single power link and a single communications link.

In fact, in a preferred arrangement, the communications interface is adapted for wireless communication through the communications channel with the remote control unit. This reduces the number of physical connections still further to just the power connection.

In an alternative embodiment, the communications channel is formed by a power signal supplied via the power connector. In this case, preferably the sealing unit further comprises a communications adaptor for detecting communications from the remote control unit carried by the power signal, and for modulating the power signal to transmit communications to the remote control unit.

In all cases, one sealing head can be exchanged much more easily for another than has been possible in the past.

Operation of a container sealing system incorporating such a sealing unit is also simplified. Thus, the remote control unit can send a single signal to the communications interface unit in order to request temperature data from the temperature sensors, the communications interface unit then polling or otherwise interrogating each temperature sensor to obtain the required information and then forwarding it back to the remote control unit.

The format of the signals for returning the temperature data can take a variety of forms. For example, each temperature sensor could be allocated an identifier which is packaged in a frame with the corresponding temperature data, the frame then being transmitted back to the remote control unit. In another option, data from the temperature sensors may be ordered in a known manner and transmitted back to the remote control unit which also knows the order and thus can identify from which temperature sensor the data comes.

In order to activate the sealing heads, the remote control unit will send a single activation signal to the communications unit which will then respond by coupling power, typically through digital switches or the like, to each sealing head. While monitoring the sealing head temperatures, if the remote control unit determines that one particular sealing head needs more or less power, it can send a suitable control signal to the communications interface unit addressed to the sealing head in question, the communications interface unit then adjusting the appropriate digital switch to vary the applied power. Again, this can be achieved using an identifier for each sealing head.

In particularly preferred embodiments, the sealing unit further comprises a memory mounted to the support connected to the communications interface unit. The provision of a memory within the sealing unit enables a number of additional advantages to be achieved. For example, the memory can hold information about the sealing heads within the unit, such as the container or tray size they are suited to seal. In addition or alternatively, the memory can store other parameters relating to the use of the sealing unit, such as desired operating temperatures for each sealing head, the number of sealing lanes, and the like, or other parameters such as type of safety system, physical dimensions of the sealing unit and "home" position. This has a further advantage that the remote control unit can check that the correct sealing unit has been fitted to the sealing apparatus by reference to the stored parameters and so prevent the apparatus running with an incorrect sealing unit fitted. Another problem with existing container sealing systems is that when a new tool or sealing unit is fitted, it is generally cold and so requires time to heat up to the correct operating temperature. Particularly in the case of a wireless communication channel but also where the channel is wired, the sealing heads could be preheated on demand from the remote control unit, even if the sealing unit was not currently fitted. In the case of a wireless communication channel, only a power connection would be required.

In the examples of preheating of sealing units via wireless communication channels, each sealing unit will have its own unique identifier which can be used by the remote control unit to select the appropriate sealing unit to preheat.

In a further example, the sealing unit further includes a local control unit adapted to enable self-heating of the sealing heads even when not mounted to sealing apparatus. This could cause self-heating on being connected to a power supply, using an internal memory device storing desired operating temperatures for the sealing heads to control the process by reference to the temperatures of the sealing heads monitored by the temperature sensors. Some examples of tray sealing systems according to the invention will now be described with reference to the accompanying drawings, in which:- Figure 1 is a schematic diagram of a first example of the system; Figure 2 is a block diagram of the primary components of the sealing unit shown in Figure 1 ; and, Figures 3 and 4 are views similar to Figures 1 and 2 but of a second example.

The tray sealing system of Figure 1 has a generally conventional form as described above. Trays are fed in a controlled, spaced apart fashion by a conveyor system (not shown) in one or more parallel lanes (not shown) to a sealing position. At the sealing position, the trays are deposited, typically having been transferred from the conveyor using gripper arms, onto a support block 1 positioned beneath a sealing unit 2. The sealing unit 2 can be moved up and down so as to bring respective heated sealing heads 3-5 into contact with plastics cover material (not shown) overlying the open tops of the trays 6-8 respectively. After the plastics material has been sealed to the trays 6-8, the sealing unit 2 is retracted and the trays removed, typically being transferred using gripper arms onto a further, downstream conveyor (not shown).

In order to control the temperature of the sealing heads 3-5, they are connected to a communications interface unit 10 located within the sealing unit 2 and this, in turn, is connected as will be described further below, to a remote control unit 12 such as a PC or other programmed control module.

The internal structure of the sealing unit 2 is shown in more detail in Figure 2. In this case, four sealing heads are provided instead of three in Figure 1 but otherwise the structures are the same.

As shown in Figure 2, the communications interface unit 10 has an I/O block 20 for connection to a communications channel 22 so as to receive and send messages from and to the control unit 12 respectively. The communications channel 22 is preferably wireless but could be hard wired.

Power is supplied to the sealing unit 2 on a line 24 where it is coupled to a power distribution block 25 having a number of outputs (four in this example) 26-29. Each power output 26-29 is connected to a respective digital switch unit

30-33 which in turn is connected to a respective one of the sealing heads 3-5 and 9.

Each digital switch 30-33 is individually controlled, so as to vary the amount of power communicated through the switch, by the communications interface unit 10 via respective hardwired connections 35-38.

Each sealing head 3-5, 9 has an associated temperature sensor 40-43 which generates an analogue signal corresponding to the sensed temperature and this is supplied via respective analogue to digital conversion blocks 44-47 to the communications interface unit 10. Finally, the communications interface unit includes a memory 50. This can, of course, be part of the interface unit or separate from it.

The memory 50 typically stores information about the sealing unit such as the desired temperatures for the different sealing heads 3-5, 9. This can be done by allocating each sealing head a unique identifier which defines a memory location at which the appropriate temperature data is stored. The memory 50 can also store other parameters as described above, and a sealing unit identifier.

In use, the sealing unit 2 is operated in a conventional manner to move it up and down to seal covers to trays. However, in order to control the temperature of the sealing heads 3-5, 9, the remote control unit 12 sends a request signal via the communications channel 22 to the communications interface unit 10 each second, the unit 10 responding to that signal to read the data currently supplied to it from the temperature sensors 40-43. That data is

then packaged into a suitable frame for transmission and sent back to the remote control unit 10 via the communications channel 22 using a conventional communications protocol. The remote control unit 10 then compares the sensor data with desired data (either obtained from the memory 50 using an appropriate request signal to the unit 10, or from otherwise stored information). If the temperature of any sealing head is different from the desired temperature, the remote control unit 12 then sends an appropriate control signal, including an identifier for the sealing head in question, to the unit 10. This supplied signal determines the amount of time the heater should be turned on as a percentage of the next second (the heaters are pulsed each second). In one example, the sealing head temperatures are fed into a PID control algorithm, which determines the amount of time the heater should be turned on as a percentage of the next second.

As mentioned above, an advantage of the invention, particularly in connection with a wireless communication channel 22, is that a sealing unit 2 which is not currently in use in sealing apparatus can be activated so as to preheat the sealing heads. Providing the sealing unit 2 is connected to a power supply, the remote control unit 12 can issue a suitable signal along the appropriate communications channel 22 to activate the sealing heads 3-5, 9 of that sealing unit. When the time is appropriate, the preheated sealing unit can then be mounted on the apparatus in place of a previous sealing unit and the sealing heads are already sufficiently heated for immediate use.

Figures 3 and 4 illlustrate a second embodiment of the invention. This embodiment is substantially the same as the first shown in Figures 1 and 2 except for the way in which power and communications signals are transmitted to and from the sealing unit 2. In this embodiment, the control unit 12 such as a CPU is coupled to a communications adaptor 50 which also receives a power supply signal from a power source 52. The communications adaptor 50 modulates the power signal from the source 52 with information from the control unit 12 and this modulated power signal is fed along the line 24 to the sealing unit 2.

As shown in Figure 4, the sealing unit 2 includes an additional communications adaptor 54 which receives the modulated power signal on the

line 24 and splits that signal into a power signal fed along a line 24' to the power distribution block 25 and a communications signal sent along the line 22, as in the previous embodiment.

When signals are to be communicated back to the control unit 12, the communications adaptor 54 is operable to modulate the power signal on the line 24 accordingly and the communications adaptor 50 can demodulate the signal to generate the communications signal which is then fed to the control unit 12.

Typically, an ethernet or etherCat communications protocol could be used for communicating along the line 24.