Device for detecting the presence of a removable tool of a linear actuator

The present disclosure relates to a linear actuator including drive means for driving a movable component assembly for actuating a tool controlled by an electronic module. In exemplary embodiments, the module comprises acquisition means for acquiring a quantity that is representative of the instantaneous force supplied by the drive means and/or the time derivative of this variable, and the electronic module is capable of controlling interruption means for interrupting the operation of the drive means if the variable does not exceed a first predetermined value during a first predetermined time period from the start of the driving of the movable component assembly, and/or if the derivative does not exceed a second predetermined value during the first predetermined time period from the start of the driving of the movable component assembly.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and benefit of French Patent Application No. 13 58088, filed Aug. 20, 2013.

BACKGROUND AND SUMMARY

The present invention relates to a linear actuator adapted to receive a removable tool and including the drive means for driving a movable component assembly for actuating the tool, controlled by an electronic module.

The invention is applicable to linear actuators, especially electro-mechanical actuators, designed for receiving a removable tool. The tool is actuated by a movable component assembly of the actuator. For example, such a tool is a tube working tool.

It is generally necessary to detect the arrival at the end of travel of the movable component assembly, as this may damage the actuator.

Patent FR-A-2 873 514 describes a linear actuator capable of receiving a removable tool, the tool being actuated by a screw driven in a translational movement, by an electric motor in both directions along its axis, designated by front and rear. This actuator includes sensors, in this case Hall effect sensors, for detecting the passage of a marker integrally attached to the screw, in this case a magnet, and for enabling the stop of the engine upon the screw reaching the end of travel in the front and/or rear directions.

Nevertheless, such an actuator does not give complete satisfaction. Indeed, the presence of the sensors results in additional manufacturing costs and increases the size and weight of the actuator.

An object of the invention is to provide an actuator having a reduced number of sensors.

To this end, the object of the invention relates to an actuator of the aforementioned type, in which the electronic module comprises the acquisition means for acquiring a variable that is representative of the instantaneous force supplied by the drive means and/or the time derivative of this variable, and in which the electronic module is capable of controlling the interruption means for interrupting the operation of the drive means if the said variable does not exceed a first predetermined value during a first predetermined time period from the start of the driving of the movable component assembly, and/or if the said derivative does not exceed a second predetermined value during the first predetermined time period from the start of the driving of the movable component assembly.

Indeed, the interruption of the operation of the drive means at the conclusion of the first predetermined time period prevents the bringing of the movable component assembly to the end stop position when no mechanical stress induced by the presence of a tool is detected.

According to particular embodiments, the invention presents one or more of the following characteristic features, taken into consideration individually or in accordance with any technically feasible combination:the electronic module is capable of controlling the interruption means for interrupting the operation of the drive means if the said derivative does not exceed a second predetermined value during the first predetermined time period from the start of the driving of the movable component assembly.the said drive means comprise an electric motor, and the said variable is the instantaneous intensity of the power supply current of the motor.the electronic module comprises the means for automatically initiating operation of the said drive means at the conclusion of the a second predetermined time period after the interruption of their operation by the said interruption means, in order to bring back the movable component assembly into an initial rest position.the actuator is powered by a battery.the electronic module comprises the means for modifying the said first predetermined time period based on the level of charge of the battery.

DETAILED DESCRIPTION

As it appears inFIG. 1, a linear actuator5comprises the means10for driving a movable component assembly15along a longitudinal axis X-X′ so as to actuate a removable tool20.

The means10are controlled by an electronic module25. The means10, the movable component assembly15and the electronic module25are arranged in a body26of the actuator5.

The actuator5comprises the fastening means27capable of cooperating with the fastening means28of the tool20in order for integrally securing the tool20to the actuator5in a removable manner.

The tool20is for example a tube working tool.

For example, the means10are formed by an electric motor30, for example, a direct current motor, and a reduction gear35.

For example, the movable component assembly15is a screw40extending along the longitudinal axis X-X′. The screw40is driven in translational linear motion along the axis X-X′ by the motor30by means of the reduction gear35, between a retracted position, shown inFIG. 1, and an advanced position of the screw40outside the body26of the actuator5.

The electronic module25controls in particular the electric power supply of the motor30supplied by a power source, for example, a battery45.

The actuator5also has a manual switch50in order to allow the user to initiate operation of the actuator5. Preferably, at the time of initiating operation, the screw40is in the retracted position.

The manual switch50is connected to the electronic module25.

As it appears inFIG. 2, the electronic module25includes a control module55connected to a power supply module60.

The power supply module60ensures the management of power supply to the motor30and is interposed between the battery45and the motor30.

The power supply module60includes the acquisition means65for acquiring the value of the instantaneous intensity of the power supply current of the motor30.

The switch50is connected to the control module55.

The control module55includes the means67for calculating the time derivative of the intensity of the power supply current.

The control module55also includes a clock75for measuring the time elapsed since the setting in operation of the linear actuator by means of the manual switch50.

The control module55in addition comprises the comparison means70for comparing the intensity of the power supply current to a first predetermined value S1, and the time derivative of the intensity of the power supply current to a second predetermined value S2, in order to actuate a main cut off switch80for cutting off power supply to the motor30if the intensity of the power supply current, and the time derivative thereof, respectively do not exceed the first predetermined value S1, and the second predetermined value S2, respectively, at the conclusion of a first predetermined time period T1 since the setting in operation of the actuator5.

Preferably, the first predetermined time period T1 depends on the level of charge of the battery45. For example, the first predetermined time period T1 is a decreasing linear function of the charge of the battery45, to compensate for the decrease in power supplied by the battery45during the course of its discharge.

The comparison means70are also capable of comparing the intensity of the power supply current to a third predetermined value S3 and the derivative of the intensity of the power supply current to a fourth predetermined value S4, in order to actuate a main cut off switch80for cutting off power supply to the motor30if the intensity of the power supply current, and the time derivative thereof, respectively, exceed the third predetermined value S3, and the fourth predetermined value S4 respectively.

The operation of actuator5will be explained in connection withFIG. 3.

FIG. 3represents the variation over time of the power current supplied to the motor30from the setting in operation of the actuator5by the manual switch50, in the event where the actuator5is equipped with the tool20, curve85, and in the event where the actuator5is not provided with the tool20, curve90. In a direct current electric motor, the intensity of the power supply current of the motor and the force supplied by the latter being proportional to each other, the curves85and90are indeed representative of the force supplied by the motor30.

FIG. 3also shows the time derivatives of the currents corresponding to the curves85and90, respectively being the curves95and100.

When the actuator5is equipped with the tool20and it is set in operation, the screw40advances out of the body26of the actuator5towards the tool20. The screw40comes into contact with a portion of the tool20. The motor30supplies an additional force in order to actuate the tool20, which results in an increase of the power current supplied to the motor30and a variation of its time derivative, as it appears over the curves85and90respectively, from 3.6 units of time.

For example, when the intensity of the power supply current of the motor30, or the value of the derivative thereof, exceeds the third predetermined value S3, and respectively, the fourth predetermined value S4, the comparison means70actuate the main switch80.

When the actuator5is not provided with the tool20and it is set in operation, in the same manner as previously noted above, the screw40advances out of the body26of the actuator5, from X to X′. The tool20being absent, the motor30supplies a substantially constant force over time so as to cause the advancing of the screw40, as it appears over the curve90in which the supply current of the motor30is substantially constant and less than the first predetermined value S1 in the interval comprised between 0 unit of time and 4.3 units of time. The derivative of the intensity of the power supply current is substantially zero, and therefore less than the second predetermined value S2, over the course of this interval, as is shown by the curve100.

At the conclusion of the first predetermined time period T1, for example 4.3 units of time inFIG. 3, the main switch80is actuated and the power supply to the motor30is interrupted. Indeed, during the first predetermined time period T1, the power supply current has remained below the first predetermined value S1 and the time derivative of this current has remained below the second predetermined value S2.

Advantageously, at the conclusion of a second predetermined time period T2 after the actuation of the main switch80, the motor30is automatically started up in order to bring back the screw40into its retracted position as illustrated inFIG. 1.

For example, the second predetermined time period T2 is comprised between 0 s and 2 s.

By way of a variant, the main switch80is actuated if, during the first predetermined time period T1, the time derivative of the power supply current of the motor30has remained below the second predetermined value S2, regardless of the value of this current.

According to another embodiment (not shown) of an actuator according to the invention, the drive means10comprises hydraulic means, for example a cylinder. The electronic module25comprises for example the means for acquiring a variable value dependent upon the instantaneous force supplied by the cylinder, for example of the fluid pressure supply of the cylinder.