GB2386958A

GB2386958A - Integral capacitive sensor for proximity detection

Info

Publication number: GB2386958A
Application number: GB0317523A
Authority: GB
Inventors: Tony Moon; Derek Bennett; Glen Wells
Original assignee: AB Automotive Electronics Ltd
Current assignee: AB Automotive Electronics Ltd
Priority date: 2003-07-28
Filing date: 2003-07-28
Publication date: 2003-10-01
Also published as: GB0317523D0

Abstract

A capacitive sensor (2) for use on a vehicle bumper (1) or body panel for proximity detection comprises a sensor that is integrally moulded into either the back face or the middle of the bumper or panel. The sensor comprises conductors (3, 5) separated by an insulating layer (4) and is held onto the bumper during the bumper moulding process whilst plastic is injected so as to seal the sensor into the bumper itself. Electrical connections (7) are made to the back of the sensor. The integrated sensor bumper unit is suitable for high volume production and removes the need for protective layers over the sensor conductors.

Description

1 2386958

Capacitive Sensor for Proximity Detection Capacitive sensors have been used for many years. W00108925 and GB2376075 disclose capacitive sensors that are used to act as aids to a driver while reversing a car, by providing warnings of an obstruction and indicating the range to the obstruction in order to be able to park tightly. A similar sensor can be fitted to the front to help judge range to an obstruction hidden from the driver's view by, for example, a high bonnet. W002084875 discloses techniques to overcome the effect of rain on such a sensor.

Several methods can be used to make suitable sensors, two of which are outlined here.

The conductors can be screen-printed on to a suitable plastic film material, then covered with an insulating coat to protect them as described in US2002 158582, or thin sheets of conductive material can be laminated on to a plastic film and protective insulating coats overlaminated. In either case, the sensor is mounted behind a car bumper or behind a plastic trim-strip that is fixed either to the bumper or the rear bodywork of the vehicle (or front for a forward sensing system).

These designs require a means to secure the sensor behind the bumper. This can either be by means of clips, a springy material to wedge it against the bumper or adhesive to secure it in place. These attachment methods all require additional parts and require additional time on the assembly line.

This patent application describes a method of making such a sensor, more suitable for high volume production by which the sensor is insert-moulded into the bumper so that the bumper and sensor form a single component.

Two variants of this process are possible. In the first variant, the sensor is made as outlined above, or described in more detail in US2002158582. The main difference is that there is no protection required on the front face of the sensor. During the process to mould the bumper, the sensor is inserted into the back surface of the mould, and held there either by an electrostatic charge or a vacuum. The mould then closes and plastic is injected all around the sensor to form the bumper. After cooling, the moulding tool is opened and a bumper is removed with the sensor moulded into its back face. Electrical connections are made to the back face of the sensor.

In the other variant of the process, the sensor has no protective coats on either side. It is inserted into the mould tool and held in place in the middle of the mould. Various techniques are available to do this; the simplest one being to hold it under tension, especially if it is made from a more rigid substrate material. Plastic is injected all around the sensor, so that it is completely enclosed in the material of the bumper.

A variant of this second process is to add connector pins to the sensor before it is inserted into the mould, and to mould the housing of the connector during the same process, so that the connector to the sensor is a part of the bumper.

Fig. 1 shows the first variant of the process, in which the sensor is on the back of the bumper skin (or trim strip). 1 is the bumper skin. The sensor assembly (2) consists of

four layers as follows: two conductors on the front (3), a plastic film substrate (4), a larger conductor on the rear (5) and an insulating protective coat (6).

Fig. 2 shows the second variant of the process in which the sensor is moulded into the middle of the bumper. 1 is the bumper skin. The sensor assembly (a) consists of three layers as follows: two conductors on the front (3), a plastic film substrate (4), and a larger conductor on the rear (5). In this variant, pins (7) have been crimped into the plastic film before insertion into the mould, and the housing for a connector (8) has been moulded around the pins so that the connector to the sensor is an integral part of the bumper / trim strip.

A variant of the design is to mould the sensor described above into a trim-strip that is fitted to a car door, a side panel or the bumper to form a proximity sensor. If fitted to a door or tailgate, the sensor can provide a warning of an obstruction when opening the door.

Claims

1. A capacitive sensor consisting of conductors, separated by an insulating sheet.

2. Capacitive sensor as in claim 1 in which any exposed surfaces of conductors are protected by an insulating film or coating.

3. A process to make a plastic panel and sensor as a single component by which a capacitive sensor as in claim I and 2 is placed securely on to the back surface of the mould and plastic is injected into the mould to form a panel with integral sensor.

4. A process to make a panel and sensor as a single component by which a capacitive sensor as in claim 1 and 2 is placed and secured in the middle of the mould cavity and plastic is injected into the mould to surround the sensor thereby forming a panel with integral sensor.

5. A panel as in claim 4 in which connector pins are attached to the conductors of the sensor and the housing of the connector is moulded into the rear face of the panel.

6. A process as in claims 3, 4 or 5 in which the panel in question is a vehicle bumper or plastic body panel.

7. A process as in claims 3, 4 or 5 in which the panel in question is a trim strip that fits into a bumper, vehicle body or vehicle door.