GB2067523A

GB2067523A - Holding sheet material on to a drum

Info

Publication number: GB2067523A
Application number: GB8034181A
Authority: GB
Original assignee: COMPUTER INSTRUMENTATION Ltd
Current assignee: COMPUTER INSTRUMENTATION Ltd
Priority date: 1980-01-18
Filing date: 1980-10-23
Publication date: 1981-07-30

Abstract

A drum (1) for feeding sheet material such as paper and holding the material during rotation of the drum about its axis by electrostatic attraction comprises a drum body e.g. of glass fibre-reinforced plastics material, provided with an elongate electrical conductor. In one embodiment, first and second electrical conductors (3 and 4) are helically wound to be equally spaced in a direction along the axis of the drum. In an alternative case, the conductors are interdigitated conductors. The conductors are encapsulated in a layer of hard epoxy material or a urethane. Electrical potentials of the same magnitude but of opposite polarity to one another are applied to respective concentric slip-rings (5 and 6) via carbon brushes (8 and 9) respectively, the latter being pressed against the slip-rings via springs (10 and 11). The arm may form part of a plotter or drafting machine. <IMAGE>

Description

SPECIFICATION Holding sheet material on to a drum by electrostatic attraction According to the present invention, there is provided a drum which comprises a cylindrical drum body whose cylindrical surface is provided with an elongate electrical conductor, there being means for applying an electrical potential to the conductor as the drum rotates about its axis for holding on to the drum, by electrostatic attraction, sheet material.

The conductor could be a conductor which extends helically around the axis of the drum.

In this case, the conductor could be a conductor applied to the drum body by winding.

Preferably, the cylindrical surface of the drum body is provided with a further such elongate electrical conductor, the said means being suitable for applying to each of the conductors an electrical potential of opposite polarity to that applied to the other of the conductors. In the case that the or each conductor extends helically around the axis of the drum, preferably the helix defined by the first conductor is offset in a direction along the axis of the drum from the helix defined by the further conductor such that the first and further conductors are equally spaced apart in a direction along the axis of the drum. Alternatively, the first and further conductors could be interdigitated conductors on the drum body.

For the or each conductor, the said means could comprise an associated slip-ring, for example one carried at an end face of the drum.

Preferably, the or each conductor is encapsulated, for example in an epoxy material or a urethane.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a view of a rotatable drum; Figure 2 is a lateral section through part of the drum; Figure 3 is a longitudinal section through part of the drum; Figure 4 shows schematically how sheet material is handled by the drum; and Figure 5 shows an alternative form of conductors of the drum.

Referring to Figs. 1,2 and 3, a rotatable drum 1 for handling sheet material such as paper comprises a drum body 2 of glass fibrereinforced plastics material on which are wound helically first and second electrical conductors 3 and 4. The helix defined by the conductor 3 is offset in a direction along the axis of the drum from the helix defined by the conductor 4 such that the conductors are equally spaced apart in a direction along the axis of the drum. Fixed at one end of the drum is a board 7 on which a pair of concentric slip-rings 5 and 6 has been provided using printed circuit techniques. Each of the slip-rings 5 and 6 is connected by a wire from the slip-ring to a respective one of the conductors 3 and 4.For applying electric potentials to the slip-rings and thereby to the conductors 3 and 4, carbon brushes 8 and 9 are pressed respectively against the slip-rings 5 and 6 by springs 10 and 11 respectively. The drum body 2 is coated with a layer 1 2 of hard epoxy material. The depth of the layer 1 2 is small compared with the separation of the conductors 3 and 4. Nevertheless, when applying the coating for providing the layer 12, sufficient must be applied to allow the coating to be machined for concentricity without danger of exposing the conductors 3 and 4.

To feed sheet material such as paper, the drum 1 is rotated about its axis and potentials of opposite polarity to one another but the same magnitude are applied to respective ones of the slip-rings 5 and 6 via the brushes 8 and 9 respectively. The effect of the charges carried by the conductors 3 and 4 is to attract and hold on to the drum by electrostatic attration the sheet material passing over the drum until separation of the sheet material and the drum, leaving substantially no residual net charge after separation. Fig. 4 shows sheet material 1 3 being fed by the drum 1, references 1 4 and 1 5 denoting separation blades.

The drum 1 may, for example, be used in a moving drum plotter or a drifting machine.

Instead of being an epoxy material, the layer 1 2 could, for example, be a urethane.

Also, for ease of manufacture, instead of using conductors 3 and 4 wound helically, a pair of conductors could be provided on the tube 2 by a screen printing process in the form of an interdigitated pattern. This is shown in Fig. 5, in which reference numerals 3' and 4' denote respective interdigitated conductors on the tube 2, each conductor comprising fingers parallel with the axis of the drum.

CLAiMS

1. A drum which comprises a cylindrical drum body whose cylindrical surface is provided with an elongate electrical conductor, there being means for applying an electrical potential to the conductor as the drum rotates about its axis for holding on to the drum, by electrostatic attraction, sheet material.

2. A drum according to claim 1, wherein the cylindrical surface of the drum body is provided with a further such elongate electri cal conductor, the said means being suitable for applying to each of the conductors an electrical potential of opposite polarity to that applied to the other of the conductors.

3. A drum according to claim 1 or 2, wherein, for the or each conductor, the said means comprises an associated slip-ring.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Holding sheet material on to a drum by electrostatic attraction According to the present invention, there is provided a drum which comprises a cylindrical drum body whose cylindrical surface is provided with an elongate electrical conductor, there being means for applying an electrical potential to the conductor as the drum rotates about its axis for holding on to the drum, by electrostatic attraction, sheet material. The conductor could be a conductor which extends helically around the axis of the drum. In this case, the conductor could be a conductor applied to the drum body by winding. Preferably, the cylindrical surface of the drum body is provided with a further such elongate electrical conductor, the said means being suitable for applying to each of the conductors an electrical potential of opposite polarity to that applied to the other of the conductors. In the case that the or each conductor extends helically around the axis of the drum, preferably the helix defined by the first conductor is offset in a direction along the axis of the drum from the helix defined by the further conductor such that the first and further conductors are equally spaced apart in a direction along the axis of the drum. Alternatively, the first and further conductors could be interdigitated conductors on the drum body. For the or each conductor, the said means could comprise an associated slip-ring, for example one carried at an end face of the drum. Preferably, the or each conductor is encapsulated, for example in an epoxy material or a urethane. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a view of a rotatable drum; Figure 2 is a lateral section through part of the drum; Figure 3 is a longitudinal section through part of the drum; Figure 4 shows schematically how sheet material is handled by the drum; and Figure 5 shows an alternative form of conductors of the drum. Referring to Figs. 1,2 and 3, a rotatable drum 1 for handling sheet material such as paper comprises a drum body 2 of glass fibrereinforced plastics material on which are wound helically first and second electrical conductors 3 and 4. The helix defined by the conductor 3 is offset in a direction along the axis of the drum from the helix defined by the conductor 4 such that the conductors are equally spaced apart in a direction along the axis of the drum. Fixed at one end of the drum is a board 7 on which a pair of concentric slip-rings 5 and 6 has been provided using printed circuit techniques. Each of the slip-rings 5 and 6 is connected by a wire from the slip-ring to a respective one of the conductors 3 and 4.For applying electric potentials to the slip-rings and thereby to the conductors 3 and 4, carbon brushes 8 and 9 are pressed respectively against the slip-rings 5 and 6 by springs 10 and 11 respectively. The drum body 2 is coated with a layer 1 2 of hard epoxy material. The depth of the layer 1 2 is small compared with the separation of the conductors 3 and 4. Nevertheless, when applying the coating for providing the layer 12, sufficient must be applied to allow the coating to be machined for concentricity without danger of exposing the conductors 3 and 4. To feed sheet material such as paper, the drum 1 is rotated about its axis and potentials of opposite polarity to one another but the same magnitude are applied to respective ones of the slip-rings 5 and 6 via the brushes 8 and 9 respectively. The effect of the charges carried by the conductors 3 and 4 is to attract and hold on to the drum by electrostatic attration the sheet material passing over the drum until separation of the sheet material and the drum, leaving substantially no residual net charge after separation. Fig. 4 shows sheet material 1 3 being fed by the drum 1, references 1 4 and 1 5 denoting separation blades. The drum 1 may, for example, be used in a moving drum plotter or a drifting machine. Instead of being an epoxy material, the layer 1 2 could, for example, be a urethane. Also, for ease of manufacture, instead of using conductors 3 and 4 wound helically, a pair of conductors could be provided on the tube 2 by a screen printing process in the form of an interdigitated pattern. This is shown in Fig. 5, in which reference numerals 3' and 4' denote respective interdigitated conductors on the tube 2, each conductor comprising fingers parallel with the axis of the drum. CLAiMS

4. A drum according to claim 3, wherein the or each slip-ring is carried at an end face of the drum.

5. A drum according to claim 3 or 4, wherein the or each slip-ring is a slip-ring produced using printed circuit techniques.

6. A drum according to any of claims 3 to 5, wherein the said means further comprises spring-loaded brush means engaging with the or each slip-ring for applying thereto electrical potential.

7. A drum according to any preceding claim, wherein the drum body comprises glass fibre-reinforced plastics material.

8. A drum according to any preceding claim, wherein the or each conductor is encapsulated.

9. A drum according to claim 8, wherein the or each conductor is encapsulated in an epoxy material.

1 0. A drum according to any preceding claim, wherein the or each conductor is a conductor which extends helically around the axis of the drum.

11. A drum according to claim 10, wherein the or each conductor is a conductor applied to the drum body by winding.

12. A drum according to claims 2 and 10 or claims 2 and 11, wherein the helix defined by the first conductor is offset in a direction along the axis of the drum from the helix defined by the further conductor such that the first and further conductors are equally spaced apart in a direction along the axis of the drum.

1 3. A drum according to claim 2 or any of claims 3 to 9 as dependent on claim 2, wherein the first and further conductors are interdigitated conductors.

14. A drum according to claim 13, wherein the conductors have been provided on the drum body by a screen printing process.

1 5. A drum according to claim 1 3 or 14, wherein each of the conductors comprises a plurality of fingers parallel with the axis of the drum and interdigitated with the fingers of the other conductor.

1 6. A drum according to claim 8 or any of claims 10 to 1 5 as dependent on claim 8, wherein the or each conductor is encapsulated in a urethane.

1 7. A drum, substantially as herein described with reference to Figs. 1, 2 and 3 of the accompanying drawings.

18. A drum, substantially as herein described with reference to Fig. 5 of the accompanying drawings.