BACKGROUND ART So-called linear units are frequently employed within industry as regards moving product linearly, i. e. vertically or horizontally, with high precision and low friction. The linear unit consists of one or more linear modules. Each linear module is driven by an electric motor, for example a servo motor. The driving proper may be put into effect via a ball screw or a cogged belt. Each linear module in principle consists of a metal profile of a length which corresponds to the intended displacement. A device for conveying the products is often placed on the linear module. The device may be placed directly on the linear module or alternatively on some form of carriage.

The linear units are to be able to displace products rapidly and with high precision. The servo motor is mostly programmed to be activated a certain predetermined time which gives a certain predetermined distance of displacement for the device of the linear module. If an incident were to occur during operation, such as a person or an object getting in the way of the device, it is important to be able rapidly to stop the motor for avoiding personal injury or material damage.

Nor are servo motors sufficiently reliable, but may be activated for a longer time than predetermined, which often results in the device forcibly striking an object and causing material damage. So-called overtravel, or the fact that something or someone gets in the way on displacement of the device may cause injury to the person or damage to the object which gets in the way of the device, as well as to electric motors, couplings and gearboxes or the device itself.

All types of safety devices for avoiding personal injury or material damage must be reliable and efficient. Safety devices in connection with linear units have previously not always been considered necessary, since transport

carried out with linear units is, on many occasions, slow. With the increased employment of linear units in that part of industry which relates to distribution equipment, the demands on well-functioning safety devices are also increasing.

The purpose of distribution equipment is to take care of products after manufacture and pack them in a suitable manner. Today, the requirements are stringent on distribution equipment, both as regards speed and precision. Linear units employed in distribution equipment are described, for example, in Swedish Patent Specification SE-9901834-3.

OBJECT OF THE INVENTION One object of the present invention is to realise a safety device in a linear unit which is reliable and efficient. The safety device is moreover simple and economical to manufacture.

SOLUTION This and other objects have been attained according to the present invention in that the safety device of the type described by way of introduction has been given the characterising feature that the device includes an end plate placed on a linear module, at least one carriage secured on the device, the carriage running on a guide rail secured on the linear module, and an indicator disposed to sense the end plate and emit a signal to the electric motor Preferred embodiments of the present invention have further been given the characterising features as set forth in the appended subclaims.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS One preferred embodiment of the present invention will now be described in greater detail hereinbelow, with particular reference to the accompanying Drawings. In the accompanying Drawings: Fig. 1 shows a safety device in normal operation; and Fig. 2 shows a safety device which has been triggered.

The Drawings show only those details essential to an understanding of the present invention, and the integration of the linear unit in, for example, a

distribution machine-which is well known to a person skilled in the art-has been omitted.

DESCRIPTION OF PREFERRED EMBODIMENT Figs. 1 and 2 show a part of a linear unit with a device. The linear unit consists of one or more linear modules 1. The linear module 1 in principle consists of a metal profile with ball-screw or cogged belt operation. The linear module 1 is driven by an electric motor, e. g. a servo motor, via gearbox and coupling. The driving of the linear module 1 is not shown on the Drawings. The linear module 1 is of a length which corresponds to that displacement which is to be realised.

The linear module 1 is provided in its one end with an end plate 2. The end plate 2 wholly covers the one end of the linear module 1 and moreover extends outside the linear module 1, at least on one side.

A device of some type is connected to the linear module 1. In the Drawings, the device consists of a gripper head 3. The gripper head 3 is intended to collect and displace a number of objects, for example packaging containers placed on an interlay sheet. The function of the gripper head 3 is described in Swedish Patent Specification SE-9901836-8. The gripper head 3 is only one example of a device which may be connected to the linear module 1, and the concept of the present invention may be applied to innumerable variations of devices connected to linear units and which are intended to convey products.

The gripper head 3 is movably connected to the linear module 1. At least one and preferably two carriages 4 are secured on the gripper head. The carriages 4 are secured each by a bracket 5. The carriages 4 are disposed each to move along a guide rail 6. The guide rails 6 are secured on opposing sides of the linear module 1, in direct connection with the end plate 2 of the linear module 1.

That end of the guide rail 6 which is turned to face away from the end plate 2 is provided with a stop 7. The stop 7 is preferably manufactured from elastic material, such as rubber, plastic or the like. The stop 7 also constitutes a stop on the upward movement of the linear module 1 in order to prevent metal from touching metal.

An indicator 8 is placed on the upper side of the gripper head 3 in connection with the end plate 2. The indicator 8 may, for example, be inductive.

The indicator 8 is secured in the gripper head 3 by means of a bracket 9. The indicator 8 is, under normal operation as shown in Fig. 1, in close contact with the end plate 2. The indicator 8 is connected to the control system of the linear unit and can emit a signal to the motor which drives the linear module 1. In the preferred embodiment, only one indicator is employed. For increased safety, indicators 8 may be placed on both sides of the linear module 1.

In normal operation, the linear module 1 moves a given, predetermined distance. This takes place in that the electric motor which drives the linear module 1 is programmed to be activated a certain time. Thus, the motor does not stop until this time has elapsed and the linear module 1 should then have covered exactly the distance which was predetermined. Throughout all of this time, the indicator 8 is in contact with the end plate 2 on the linear module 1 and no signal is given to the motor.

In the event of a possible operational disruption, for example that someone or something gets in the way of the movement of the gripper head 3, the safety device is to be triggered. Without the safety device, serious injury or damage could occur, both personal injury and material damage. As far as the equipment is concerned, this could involve damage to the motor, coupling, gearbox and/or to a device connected to the linear module 1. Operational disruptions can also occur in that the motor is activated for too long a period of time, so-called overtravel. This is particularly prone to occur when servo motors are employed.

When the gripper head 3 or other device connected to the linear module is stopped in its movement while the motor is still activated, the gripper head 3 will be lifted in relation to the linear module 1 in that the carriages 4 are moved upwards along the rails 6. This is illustrated in Fig. 2. When the gripper head 3 is lifted in relation to the linear module 1, the indicator 8 which is secured on the gripper head 3 will lose contact with the end plate 2 secured on the linear module 1. The indicator 8 emits a signal to the control system and the motor of the linear module 1 stops. The length of the guide rail 6 is determined by the stop distance which the motor needs.

By, as in the preferred embodiment, providing two carriages 4 and guide rails 6 placed on opposite sides of the linear module 1, the gripper head 3 will be lifted straight up even if the obstacle which the gripper head 3 rams is at the one edge of the gripper head 3. If only one carriage 4 and guide rail 6 is employed, there is a risk of damage to the gripper head 3 as a result of the displacement which can then occur.

The safety device according to the present invention may also be employed for positioning at moderate speeds. In that a device such as the gripper head 3 is lifted when it strikes against something, a signal will be received to the effect that the device has arrived, in that the indicator 8 then is no longer in contact with the end plate 2 on the linear module 1. The motor stops and the device has reached its position.

As will have been apparent from the foregoing description, the present invention realises a safety device intended for a linear unit which is reliable and efficient. The safety device can prevent personal injury or material damage, at the same time as it is economical to manufacture and simple to assemble.