GB2536189A - Automated printing process and apparatus - Google Patents

Abstract

An automated printing system comprises a tampographic printing unit 8 having a plurality of printing pads (10, Fig.1) configured to perform respective printing cycles. The printing unit has a drive module for operating said printing unit in accordance with predefined instructions, said predefined instructions controlling a plurality of required printing cycles in respect of a single substrate. The printing unit also has at least one robotic arm 5 comprising a holding device 6 for holding a substrate to be printed. The robotic arm is configured to allow six degrees of freedom of movement of a substrate held by said holding device, in use. A control unit 1 is associated with said robotic arm and is communicably coupled with a storage device having stored therein data representative of said predefined instructions for controlling the robotic arm. The substrates to be printed may be moved via a conveyor unit 2. There is also provided a method of controlling the robotic arm.

Description

AUTOMATED PRINTING PROCESS AND APPARATUS

This invention relates generally to an apparatus and method for automated printing of substrates and, more particularly, to an automated pad printing process and apparatus for enabling a plurality of substrates on a production line to be printed with minimal human intervention.

Pad printing, or tampography, is a printing process that can transfer a two-dimensional image onto a three-dimensional object. This is accomplished using an indirect offset printing process that involves an image being transferred from the cliché, via a silicone pad, onto a substrate. Pad printing is used for printing on otherwise difficult to print on products in many industries including medical, automotive, promotional, apparel, and electronic objects, as well as appliances, sports equipment, commercial and industrial safety equipment, and toys.

Referring to Figure 1 of the drawings, a typical pad printing system comprises a unit carrying one or more transfer pads 10 at the ends of respective transport mechanisms 12. The transport mechanisms 12 are coupled to drive means (not shown) for driving them up and down (A) and back and forth (B), as required. The printing pads 10 are three dimensional devices, typically molded of silicone rubber, and may be of any required size and shape, depending on the application.

The unit further comprises, in respect of each transfer pad 10, an image plate 14, having the desired artwork "image" etched into its upper surface, and a sealed ink cup system 16 in the form of a sealed container which provides an ink supply for the respective transfer pad 10. In the "home" position, the sealed ink cup 16 sits over the etched artwork area of the image plate 14, covering the image.

In front of the printing unit, a conveyor system 18 is provided, which includes an elongate rail 20 and motive means (not shown) for conveying a support mechanism 22 back and forth along axis D. The support mechanism 22 includes a rotational head (not shown) on which is supported a substrate 24 to be printed, in this case a safety helmet. The rotational head allows the substrate 24 supported thereon to be rotated about two distinct axes, as illustrated by arrows E and F in Figure 1, depending on the location on the substrate on which an image is to be printed. Typically, a printing unit would comprise, say, four or six printing pads arranged in a row, each for printing a different colour and/or image on the substrate, and the system would be programmed such that the substrate is moved back and forth along the rail and subjected to a sequence of printing cycles from each pad. However, for simplicity, only one is shown in Figure 1.

In use, from the home position, the sealed ink cup 16 fills the etched artwork area of the image plate 14 with ink. The ink cup 16 then moves away (along axis C) from the etched artwork area, taking all the excess ink and exposing the etched image, which is filled with ink. The top layer of ink becomes tacky as soon as it is exposed to the air; that is how the ink adheres to the transfer pad 10 and later to the substrate 24.

The transfer pad 10 moves in toward the printing unit and then presses down onto the printing plate 14 momentarily. As the pad 10 is compressed, it pushes air outward and causes the ink to lift (transfer) from the etched artwork area onto the pad. As the transfer pad 10 lifts away, the tacky ink film inside the etched artwork area is picked up on the pad. A small amount of ink remains in the printing plate.

The transfer pad 10 then moves forward, and the ink cup 16 also moves to cover the etched artwork area on the printing plate 14 once again. The ink cup 16 again fills the etched artwork image on the plate 14 with ink in preparation for the next cycle. The transfer pad 10 then compresses down onto the substrate 24, transferring the ink layer picked up from the printing plate to the substrate surface. Then, it lifts off the substrate 24 and returns to the home position, thus completing one print cycle.

In conventional pad printing systems, for each printing event, a human user must manually place a substrate on the support member 22 and actuate the printing process for that substrate. The user then removes the substrate, and places another substrate onto the support member before starting the printing process again. On the other hand, it is not possible to use a linear conveyor belt carrying a number of substrates to be printed sequentially, because the printing process for a single process usually requires it to be moved back and forth along the line of printing pads in order for all artwork to be transferred to each required surface of the substrate. Printing a single substrate at a time, and requiring human intervention to load and unload each substrate before starting a printing process is very time consuming and results in a low throughput, compared with other printing processes, which may have an automated feed and loading mechanism. However, for many substrate types, pad printing is the best or only option for effective printing.

It would, therefore, be desirable, to provide a pad printing process and system which incorporates an element of automation in relation to loading and unloading of substrates, such that large numbers of substrates can be printed without significant human intervention. However, there are a number of problems associated with this, which has prevented such automation from being realised. Firstly, an automated loading and unloading mechanism would be controlled by software code, which is inherently incompatible with the code used to control known pad printing systems. Synchronising two incompatible systems so that loading/unloading occurs at exactly the right time to allow effective and accurate printing is not a trivial issue and has, until now, provided a significant bar to automating pad printing processes. Furthermore, pad printing mechanisms inflict a large force, for example 20kg or more, on the substrate during the printing step. In conventional systems, where a single, robust support member including a support head is provided for each substrate, this force can be withstood and does not cause an issue. However, with any degree of automation, this issue becomes a major consideration.

Aspects of the present invention are intended to address at least some of these issues and, in accordance with the present invention, there is provided an automated printing system, comprising: -a tampographic printing unit comprising a plurality of printing pads configured to perform respective printing cycles, the printing unit having a drive module for operating said printing unit in accordance with predefined instructions, said predefined instructions controlling a plurality of required printing cycles in respect of a single substrate; - at least one robotic arm comprising a holding device for holding a substrate to be printed, said robotic arm being configured to allow six degrees of freedom of movement of a substrate held by said holding device, in use; and - a control unit, associated with said robotic arm and communicably coupled with a storage device having stored therein data representative of said predefined instructions, the control unit being configured, in use, to, repeatedly: o cause said robotic arm to grip a substrate, by means of said holding device, and move said substrate to a first position for performance of a first printing cycle; o transmit a signal to said drive module of said printing unit to actuate said first printing cycle; o receive a signal from said drive module of said printing unit indicative that said first printing cycle has been completed; o cause said robotic arm to move said substrate to a second position for performance of a second printing cycle; o transmit a signal to said drive module of said printing unit to actuate said second printing cycle; o receive a signal from said drive module of said printing unit indicative that said second printing cycle has been completed; and o when all of the printing cycles for said substrate have been completed, cause said robotic arm to release said substrate.

One of the features that facilitates this level of automation of a tampographic printing process is the fact that operation of the printing unit is actuated and controlled by the robotic arm control unit. Thus, each step of a full set of printing cycles is controlled in accordance with operation of the robotic arm and synchronisation between the two independent units can thus be effectively achieved by means of a "handshake" protocol, which requires the printing unit to wait between each printing cycle for an actuation signal from the robotic arm control unit. Communication between the robotic arm control unit and the tampographic printing unit is not a trivial issue, and requires the use of an architecture which defines a number of intermediate communication layers between the two principal controllers. In one exemplary embodiment of the invention, such communication may be effected via an intermediate, generic programmable logic controller (PLC), such as a Siemens ® PLC, with data transfer from the drive module of the printing unit to the PLC being effected via a process field bus (PROFIBUS), and communication between the PLC and the robotic arm control unit being effected via an Ethernet connection such as PROFINET.

The storage device, to which the robotic arm control unit is communicably coupled, may contain data representative of the predefined instructions in the form of offsets, representative of the above-mentioned six degrees of freedom, which accurately define the precise required position of the substrate in respect of the printing unit for performance of each printing cycle.

As explained above, another problem can arise in respect of the force applied to the substrate (and, therefore, the robotic arm) each time a printing cycle is completed. Clearly, the repeated application of a 20kg (or greater) force to a robotic arm is likely to result in excessive wear and premature failure of the device. Thus, in an exemplary embodiment of the invention, the system includes a support unit comprising, in respect of each printing pad of the printing unit, a rigid support device, and the robotic arm control unit is configured to move the robotic arm to a position for performance of each printing cycle, such that the substrate rests on a respective support device which, in turn, absorbs a significant proportion of the force of each printing operation.

Each substrate for printing can be manually placed on a linear conveyor mechanism in a position suitable for the robotic arm to sequentially grip and lift each substrate to be printed in turn. After each printing operation, the robotic arm may be configured to move the substrate to a receptacle or other receiving means, before releasing it.

In one exemplary embodiment of the invention, the system may comprise two or more robotic arms, such that more than one substrate can be printed at a time. In this case, it is envisaged that a single control unit may be employed to control operation of the robotic arms and the printing unit, with the printing cycles of the same printing process being performed in a different order in respect of each respective substrate.

The resultant increase in potential throughput is highly commercially advantageous, and is facilitated by the architecture and configuration of the claimed invention. The number of robotic arms and, therefore, the number of substrates that can be printed at the same time, is limited only by the number of pads on the printing unit itself and the space available to accommodate the system.

Another aspect of the present invention extends to an automated method of tampographic printing using a system as described above, the method comprising: - repeatedly: o causing said robotic arm to grip a substrate, by means of said holding device, and move said substrate to a first position for performance of a first printing cycle; o transmitting a signal to said drive module of said printing unit to actuate said first printing cycle; o receiving a signal from said drive module of said printing unit indicative that said first printing cycle has been completed; o causing said robotic arm to move said substrate to a second position for performance of a second printing cycle; o transmitting a signal to said drive module of said printing unit to actuate said second printing cycle; o receiving a signal from said drive module of said printing unit indicative that said second printing cycle has been completed; and o when all of the printing cycles for said substrate have been completed, causing said robotic arm to release said substrate.

Another aspect of the present invention extends to a method of manufacturing an automated printing system as described above, comprising: providing a tampographic printing unit comprising a plurality of printing pads configured to perform respective printing cycles, the printing unit having a drive module for operating said printing unit in accordance with predefined instructions, said predefined instructions controlling a plurality of required printing cycles in respect of a single substrate; providing at least one robotic arm comprising a holding device for holding a substrate to be printed, said robotic arm being configured to allow six degrees of freedom of movement of a substrate held by said holding device, in use; - providing a control unit, associated with said robotic arm and communicably coupled with a storage device having stored therein data representative of said predefined instructions; and configuring the control unit to, in use, repeatedly: o cause said robotic arm to grip a substrate, by means of said holding device, and move said substrate to a first position for performance of a first printing cycle; o transmit a signal to said drive module of said printing unit to actuate said first printing cycle; o receive a signal from said drive module of said printing unit indicative that said first printing cycle has been completed; o cause said robotic arm to move said substrate to a second position for performance of a second printing cycle; o transmit a signal to said drive module of said printing unit to actuate said second printing cycle; o receive a signal from said drive module of said printing unit indicative that said second printing cycle has been completed; and o when all of the printing cycles for said substrate have been completed, cause said robotic arm to release said substrate.

These and other aspects of the present invention will become apparent from the following specific description in which embodiments of the invention are described, by way of examples only, and with reference to the accompanying drawings, in which: Figure 1 is a schematic partial perspective view of a tampographic printing system according to the prior art; Figure 2 is a schematic perspective view of a system according to an exemplary embodiment of the present invention; Figure 3a is a schematic front view of a substrate holder for use in a system according to an exemplary embodiment of the present invention; Figure 3b is a schematic perspective view of a substrate holder for use in an exemplary embodiment of the present invention, including thereon a substrate to be printed; Figure 4 is a schematic block diagram illustrating a communication architecture for use in a system according to an exemplary embodiment of the present invention; Figure 5 is a schematic perspective view of a gripper for use in a system according to an exemplary embodiment of the present invention, including thereon a substrate to be printed; Figure 6a is a partial schematic perspective view of a support unit for use in a system according to an exemplary embodiment of the present invention, including thereon a substrate to be printed; and Figure 6b is a schematic front view of a support unit for use in a system according to an exemplary embodiment of the present invention.

Referring to Figure 2 of the drawings, an automated printing system according to an exemplary embodiment of the present invention comprises a computer-implemented control unit 1, associated with a pair of jointed arm robots 5. A conveyor roller unit 2, comprising a plurality of sequential substrate holders 2a is located in front of, and spaced apart from, a tampographic pad printing unit 8, with the robots 5 therebetween. Each robot 5 is provided, at its distal end, with a respective gripper 6 for gripping a substrate to be printed, and a flamer 7 is provided in respect of each robot 5 for pre-treating each substrate prior to printing. The flamer 7 breaks the surface tension of the polymer material of which the substrate 24 is formed, which has the effect of improving print finishing quality. A suction turner 9a is provided for removing a printed substrate from a robot 5 and placing the substrate on an outbound conveyor belt 9.

In use, the control unit 1 causes a first robot 5 to move to the pick up point 4 on the conveyor belt, and grip the substrate located there before lifting and moving it, via the associated flamer 7, to a position relative to the printing unit 8 for performance of a first printing cycle of a complete substrate printing process. When the pick up point 4 has been vacated, the next substrate in the sequence moves, via the conveyor unit 2, into the pick up point 4 and the control unit 1 causes the second robot to move to the pick up point 4 and grip the substrate located there before lifting and moving it, via the associated flamer 7, to another position relative to the printing unit 8 for performance of another printing cycle in the same printing process. When each respective robot is in the correct position, a signal is transmitted from the control unit 1 to the printing unit 8, causing it to perform the respective printing cycles, following which the printing unit transmits completion signals back to the control unit 1 to indicate that the printing cycles have been completed. In response to the respective completion signals, the control unit 1 causes the robots 5 to move the substrates to further locations relative to the printing unit for performance of further respective printing cycles of the complete substrate printing process, and this is repeated, with the printing unit transmitting completion signals back to the control unit 1 in respect of each completed printing cycle, until a complete printing process has been completed for each substrate. The control unit 1 then causes the suction turner 9a to remove, by suction, each printed substrate from the respective robots 5 and place them on the outbound conveyor belt 9 to be transported elsewhere for checking, packaging, etc. This process is then repeated for another pair of substrates, and continued until a complete batch has been completed. Thus, it can be seen, that the control unit 1 coordinates multiple printing cycles or steps for the two robots 5, orchestrating the movement thereof and their application, so as to maximise efficient use of time and avoid clashes/conflicts between the robot movements.

Referring to Figures 3a and 3b of the drawings, the substrates 24 may comprise safety helmets, and the substrate holders 2a may comprise a plate on which is provided a pair of rigid, upstanding bars defining opposing ridges at their upper ends, such that when a helmet 24 is placed thereon, with the open end facing upward, the ridges engage with side slots in the helmet to support and stabilise it. A padding material, such as felt or the like, may be provided within the ridges and/or the inner surfaces of the upstanding bars so as to protect the outer surface of the substrate from damage, such as scratching. In one exemplary embodiment of the invention, the helmets 24 are manually placed in the correct orientation, and with the helmet peak facing outward, by an operative. The operative can determine visually whether or not the helmet has been correctly loaded, but in an exemplary embodiment, a sensor and alarm system may be employed to alert a user to incorrect loading, if required. A plurality of substrate holders 2a are provided on a continuous conveyor roller unit 2.

As described above, the operation of each printing process is controlled by the robot control unit 1, with the operation of the drive module of the printing unit being controlled in accordance with actuation signals originating from the robot control unit, in order to ensure accurate synchronisation between to two distinct systems. Since the control mechanisms of the two systems are necessarily distinct, in order to enable the two systems to communicate effectively with each other, an intermediate architecture, such as that shown in Figure 4 is provided. As shown, the communication architecture employed in an exemplary embodiment of the present invention comprises an intermediate PLC which communicates with the drive module 8a of the printing unit via process field bus PROFIBUS, and communicates with the robot control unit 1 via an Ethernet connection PROFINET. As shown, the database 31, in which the predefined instructions representative of the printing cycles of a complete substrate printing process is associated with, and communicably couple to, the robot control unit 1.

Referring to Figure 5 of the drawings, the gripper 6 provided at the distal end of each robot 5 comprises a central drive block 32 with a pair of gripping plates 34 extending from opposing sides thereof. The gripping plates 34 are mounted on the drive block 32 for lateral movement along a horizontal axis, away from and toward the sides of the drive block 32. Before a helmet is gripped, the gripping plates 34 are in a first position, closest to the sides of the drive block 32. The gripper 6 is placed into an upturned helmet and the gripping plates are caused to move outwardly, away from the sides of the drive block and onto the inner side walls of the helmet, thereby applying sufficient pressure on the inner side walls of the helmet to grip it, but without stretching or damaging the plastic helmet shell. Once gripped, operation of the robot enables the helmet to be oriented accurately and quickly for multiple print positions, for example, rear of shell, right side of shell, left side of shell, front of shell, etc. Referring to Figures 6a and 6b of the drawings, and not shown in Figure 2 of the drawings, a system according to an exemplary embodiment of the present invention may comprise a support unit 36 located in front of, adjacent to and substantially parallel with the printing unit. The support unit 36 comprises a plurality of spaced apart support braces 38, with one support brace being provided and located immediately in front of each print head (or pad) of the printing unit. Each support brace 38 comprises a pair of parallel, upstanding arms 40, on the upper end of each of which is provided a cylindrical support member 42 oriented substantially orthogonally to the respective arm 40. In use, when the robot places the substrate 24 in a location relative to the printing unit for performance of a printing cycle, a neck portion 44 of the gripper 6 rests on a respective cylindrical support member 42, such that when the printing operation is performed, the support brace 38 absorbs most of the force, thus improving the longevity of the robots and avoiding unnecessary wear. The support braces are configured to be raised and lowered relative to the printing unit in response to one or more activation signals from the control unit 1. In one exemplary embodiment, all of the support braces 38 may be configured to be raised at the same time at the start of a printing sequence or process, in response to a single activation signal from the control unit 1, and remain raised until a complete substrate printing process is complete. In alternative exemplary embodiments, however, a sequence of activation and deactivation signals from the control unit 1 may be used to selectively raise and lower individual support braces 38 as required. In Figures 6a and 6b, all of the support braces 38 are shown in the raised, operative position.

Whilst specific exemplary embodiments of the present invention have been described in detail above, it will be apparent to a person skilled in the art that modifications and variations can be made to the described embodiments without departing from the scope of the invention, as claimed.

Claims (10)

1. CLAIMS1. An automated printing system, comprising: - a tampographic printing unit comprising a plurality of printing pads configured to perform respective printing cycles, the printing unit having a drive module for operating said printing unit in accordance with predefined instructions, said predefined instructions controlling a plurality of required printing cycles in respect of a single substrate; - at least one robotic arm comprising a holding device for holding a substrate to be printed, said robotic arm being configured to allow six degrees of freedom of movement of a substrate held by said holding device, in use; and - a control unit, associated with said robotic arm and communicably coupled with a storage device having stored therein data representative of said predefined instructions, the control unit being configured, in use, to, repeatedly: o cause said robotic arm to grip a substrate, by means of said holding device, and move said substrate to a first position for performance of a first printing cycle; o transmit a signal to said drive module of said printing unit to actuate said first printing cycle; o receive a signal from said drive module of said printing unit indicative that said first printing cycle has been completed; o cause said robotic arm to move said substrate to a second position for performance of a second printing cycle; o transmit a signal to said drive module of said printing unit to actuate said second printing cycle; o receive a signal from said drive module of said printing unit indicative that said second printing cycle has been completed; and o when all of the printing cycles for said substrate have been completed, cause said robotic arm to release said substrate.
2. 2. A system according to claim 1, comprising a communication architecture between said printing unit drive module and said robotic arm control unit, the architecture comprising an intermediate programmable logic controller (PLC), wherein data transfer from the drive module of the printing unit to the PLC is effected via a process field bus, and communication between the PLC and the robotic arm control unit is effected via an Ethernet connection.
3. 3. A system according to claim 1 or claim 2, wherein the storage device, to which the robotic arm control unit is communicably coupled, contains data representative of the predefined instructions in the form of offsets, representative of said six degrees of freedom, which define the precise required position of said substrate in respect of the printing unit for performance of each printing cycle.
4. 4. A system according to any of the preceding claims, including a support unit comprising, in respect of each printing pad of the printing unit, a rigid support device, wherein the robotic arm control unit is configured to move the robotic arm to a position for performance of each printing cycle, such that the substrate rests on a respective support device.
5. 5. A system according to any of the preceding claims, further comprising a linear conveyor mechanism for sequentially conveying a plurality of substrates for printing to a position suitable for the robotic arm to grip each substrate to be printed.
6. 6. A system according to any of the preceding claims, wherein the robotic arm is configured to move a printed substrate to a receptacle or other receiving means, before releasing it.
7. 7. A system according to any of the preceding claims, comprising two or more robotic arms.
8. 8. A system according to claim 7, comprising a single control for controlling operation of the robotic arms and the printing unit, with the printing cycles of the same printing process being performed in a different order in respect of each respective substrate.
9. 9. An automated method of tampographic printing using a system according to any of the preceding claims, the method comprising: - repeatedly: o causing said robotic arm to grip a substrate, by means of said holding device, and move said substrate to a first position for performance of a first printing cycle; o transmitting a signal to said drive module of said printing unit to actuate said first printing cycle; o receiving a signal from said drive module of said printing unit indicative that said first printing cycle has been completed; o causing said robotic arm to move said substrate to a second position for performance of a second printing cycle; o transmitting a signal to said drive module of said printing unit to actuate said second printing cycle; o receiving a signal from said drive module of said printing unit indicative that said second printing cycle has been completed; and o when all of the printing cycles for said substrate have been completed, causing said robotic arm to release said substrate.
10. 10.A method of manufacturing an automated printing system according to any of claims 1 to 8, comprising: - providing a tampographic printing unit comprising a plurality of printing pads configured to perform respective printing cycles, the printing unit having a drive module for operating said printing unit in accordance with predefined instructions, said predefined instructions controlling a plurality of required printing cycles in respect of a single substrate; - providing at least one robotic arm comprising a holding device for holding a substrate to be printed, said robotic arm being configured to allow six degrees of freedom of movement of a substrate held by said holding device, in use; - providing a control unit, associated with said robotic arm and communicably coupled with a storage device having stored therein data representative of said predefined instructions; - and configuring the control unit to, in use, repeatedly: o cause said robotic arm to grip a substrate, by means of said holding device, and move said substrate to a first position for performance of a first printing cycle; o transmit a signal to said drive module of said printing unit to actuate said first printing cycle; o receive a signal from said drive module of said printing unit indicative that said first printing cycle has been completed; o cause said robotic arm to move said substrate to a second position for performance of a second printing cycle; o transmit a signal to said drive module of said printing unit to actuate said second printing cycle; o receive a signal from said drive module of said printing unit indicative that said second printing cycle has been completed; and o when all of the printing cycles for said substrate have been completed, cause said robotic arm to release said substrate.