GB2085190A - Power machine control apparatus - Google Patents

Abstract

When the mobile unit (5) of the machine, such as a press-platen, makes contact with fixed parts (for example by impact between the tool and the piece to be worked), there is an immediate slowing down of the mobile unit, even before, for example, the oil pressure of the hydraulic control system for the mobile unit increases, which is detected by a sensor (9, 10) constructed as an optical device providing a signal having a frequency proportional to speed. At a minimum threshold signal from the device a predetermined programme is initiated by a computer, or programmer, 7. The device may alternatively be used in a safety system. <IMAGE>

Description

SPECIFICATION Power machine control apparatus The invention relates to power machines in general, which comprise a mobile unit. A particular but not exclusive example is that of a press. This particular application is referred to hereinafter, but without this representing a limitation.

According to the invention, the apparatus firstly comprises sensor means arranged to evaluate an instantaneous reduction in the speed of movement of the mobile unit which occurs when this interferes with a working or accidental obstacle. The apparatus also comprises actuator means which depend on said sensor means and are arranged to determine programmed commands as a function of, in consequence of, and starting from a speed reduction cycle provided by said sensor means.

It is therefore possible to determine a sequence of commands starting from the moment and/or position of initial impact between the mobile unit (and in particular a tool) and the piece to be worked. It is also possible to obtain a stoppage or a reversal of motion when there is accidental interference in a position appreciably distant from the zone of presumable contact with a piece to be worked. In this case, the apparatus operates as a safety device.

The apparatus can comprise a programmer arranged to establish a sequence of operations in accordance with position data obtained by the sensor means.

The sensor means can be advantageously represented by a transducer which besides evaluating the absolute (or relative) position of the mobile unit, generates signals in the form of variations of a quantity, for example of a frequency of pulses read from a graduated rod parallel (or otherwise) to the direction of movement of the mobile unit, thus evaluating the variations in the speed of the mobile unit.

The invention also relates to a method for programming and controlling the movements of a power machine comprising a mobile member. This method is based on the fact that the variation in the speed of said mobile member is evaluated at the moment in which interference with an obstacle takes place, and programmed commands are provided in accordance with the position and the moment in which said speed variation occurs.

The invention will be more apparent from the description and accompanying drawing which shows a non-limiting embodiment of the invention, and in which: Figure 1 is a diagrammatic front view of a press to which the apparatus according to the invention is fitted; and Figure 2 is a side view of said press.

As shown on the accompanying drawing, the reference numeral 1 indicates the base structure of a press, 3 the upper structure thereof and 5 the visible part of the mobile unit. The programmer assembly 7 is provided to the side. There is also provided a unit for measuring the speed and the variation in the speed of the mobile unit. For this purpose, according to the drawing, in the fixed part there is disposed an optical rod 9 comprising optical reading graduations of conventional type. With the optical rod or bar 9 there cooperates an optical reading part 10, i.e. a slider, arranged to read the signs on the optical bar, and generate signals the frequency of which is proportional to the speed. As an alternative, the measuring unit can consist of a magnetic system (Inductosyn type) with a fixed part and a mobile part.

The descent movement of the mobile unit 5 of the press (or the movement of any other machine) can comprise a fast approach stroke followed by a slowing down to allow greater fineness of response in the vicinity of the working part of the stroke of the mobile unit. A suitable frequency, preferably high to give greater measuring fineness, can be read for example at the normal speed in the vicinity of the working zone. At the moment in which interference, i.e. contact with an obstacle represented by the piece to be worked occurs, the reading frequency falls because the working unit under examination undergoes an immediate even though temporary slowing down because of the increase in the force.When the falling frequency passes a predetermined minimum threshold value - which differs to a greater or lesser extent from the frequency associated with the slowed-down approach according to whether it is required to cause the control to take place with lesser or greater accuracy in evaluating the moment in which the slowing-down process begins - the computer or other control device generates a signal for initiating a predetermined programme.

This programme can comprise for example a further stroke of limited extent (the active pressing or piece incision stroke) and/or a predetermined pressure for acting on the piece and/or a command for the operation of an external unit or the return whenever the impact has taken place in a zone other than the predetermined zone, etc. It is apparent that these commands are set up, starting from a determined origin, by the initial impact (wherever and at whatever moment it arises) between the mobile part and the fixed part, and in particular for example the impact between the punching tool and the piece to be worked lying on the machine.

When the programmed cycle has ended, the working unit is returned to the position of origin and the same cycle can be repeated, or a further cycle can be carried out such as a second pressing cycle or successive pressing or straightening blows, the new cycle also being started from the moment in which the mobile unit encounters the new position assumed by the piece after the first (or the preceding) punching operations.

An analogous application can be as a safety device for return in the case of the presence of an accidental obstacle. In this case, as already stated, the return can be obtained whenever impact takes place in a zone other than the predetermined zone, i.e. in the presence of an obstacle.

It is apparent that the origin of a cycle or of various cycles can be easily changed by moving the initial zero, without the working cycle having to vary other than by variation of the unloaded stroke, and without influencing the operation of the pressure switch, the sensitivity and readiness of which are always much less than those of the apparatus according to the invention.

The operation of the apparatus is therefore based on the principle of the variation - even minimal and instantaneous - of the speed of a mobile part, with the action threshold adjustable within wide limits and with extreme accuracy and timeliness of action.

It is therefore possible for example to carry out an incision'of constant depth even if the characteristics of the material and/or the dimensions of a piece inserted in a press vary.

A further possible application is as a safety device for machine tools either controlled by numerical control or otherwise, by determining the moment in which an undesired contact takes place, by means of dimension measuring members or by means of signals emitted by members for monitoring the speed of movement (for example a tachometer dynamo).

An apparatus of the aforesaid type can be fitted to any machine by simply connecting the measuring member to the working unit and by connecting to the computer and to the programmer.

The drawing shows only one embodiment given by way of example, and modifications can be made to the shapes and arrangements without leaving the scope of the inventive concept.

Claims (9)

1. An apparatus for programming and controlling movements of a power machine comprising a mobile unit which makes working movements, said apparatus characterised by comprising sensor means arranged to evaluate an instantaneous reduction in the speed of movement of said mobile unit when this interferes with a working or accidental obstacle; and actuator means dependent on said sensor means for determining programmed commands as a function of and in consequence of a speed reduction signal provided by said sensor means.

2. An apparatus as claimed in the preceding claim, characterised by comprising a programmer arranged to establish a sequence of operations in accordance with position data obtained by said sensor means.

3. An apparatus as claimed in the preceding claims, characterised in that the sensor means are arranged to evaluate the position (absolute or relative) of the mobile unit.

4. An apparatus as claimed in the preceding claims, characterised by comprising a transducer for estimating and processing the variation in the speed of the mobile unit, in particular in the form of a frequency variation.

5. An apparatus as claimed in the preceding claims, characterised by being applied to a press, the sensor means being arranged to evaluate the position and moment in which contact takes place with the piece to be worked, which represents the braking obstacle for the mobile unit of the press.

6. An apparatus as claimed in the preceding claims, characterised in that the sensor means are arranged to signal interference with an accidental obstacle.

7. An apparatus as described and illustrated.

8. A method for programming and controlling movements of a power machine comprising a mobile member, characterised in that the variation in the speed of said mobile member is evaluated on the occasion of the initial interference with an obstacle, and commands are provided in accordance with the position and the moment in which said speed variation occurs.

9. A method for programming and controlling the movements of a power machine as defined and using the apparatus claimed.