The present invention relates to portable pneumatic machines of the type having a body with a compressed air inlet pipe or tube, rotary pneumatic drive means (bladed turbine or motor for exemple) placed in the body, actuated by the compressed airflow for rotating a tool, a device for adjusting or stopping the airflow feeding the machine and an electric generator including a rotor and a stator installed in the body. The rotor is arranged for being mechanically rotated by the drive means forcreating electric energy from the pneumatic power driving the tool.
The invention is particularly suitable, though not exclusively, for portable pneumatic screw drivers, drills, screwers and grinders.
Pneumatic machines of the above defined type are already known. The document FR-A-No. 2 523 891, relating to a rotary pneumatic machine which includes lighting, shows a machine with a rotary member driven by a mechanism enclosed in a case, andactuated by compressed air. The case, having for this purpose means for connection to a compressed air source, includes an electric generator with rotor and stator, the rotor of which is driven by the compressed air feeding mechanism of the machine. This rotor is enclosed in a housing fixable to the case. The generator energizes lightening means carried by the housing for allowing the machine to work in difficult accessible places where the use of a portable lamp is impossible. This machinenevertheless only has a limited interest.
It is another object of the invention to provide a machine including an electric generator having signal delivering means which comprise third signal means delivering a signal representative of the rotational speed of the rotary drive means. Theelectronic circuit for controlling and monitoring the machine has third selecting means for selecting a reference value of this speed and means for maintaining said speed at this reference value. An application of this particularly interestingembodiment may be made to grinders, sanders and other machines whose speed of rotation depends on the pressure exerted by the operator on the support to be machined.
Another object of the invention is to provide a pneumatic machine wherein the signal delivering means of the electric generator means include second signal means for transmitting to the electronic circuit a signal representative of the angularposition of the rotary drive means and of the tool, said electronic circuit having second selecting means for selecting a reference value of the angular position of the tool and for controlling the actuating device when the angular position of the toolreaches said reference value. With this arrangement, a screw may be screwed into a support of variable elasticity. An approximative approach brings the support and the screw into contact, this latter than being rotated through a predetermined angle.
Another object of the invention is to provide a portable pneumatic machine wherein the signal delivering means include first signal means for transmitting to the electronic circuit a signal representative of the torque exerted by the rotary drivemeans on the tool, said electronic circuit having first selecting means for selecting a torque reference value for the maximum output torque value of said rotary drive means and for controlling the actuating device when the torque value has reached saidreference value. When the torque has reached the reference value, the air is cut off.
An object of the invention is also to provide a portable screw driver wherein the electronic circuit further comprises measuring means for measuring the torque value increase during operation of the machine with respect to time, firstanticipating means for anticipating from said measuring of the torque value increase a remaining torque value increase necessary to follow for reaching the torque reference value, computing means setting a reference time to and deducing from saidremaining torque value increase a remaining tightening time t from said reference time to for reaching said torque reference value, and means for actuating the actuating device arranged to shut off the compressed air inlet pipe after the time tstarting from said reference time to, whereby the tool is precisely stopped when the torque reference value is reached.
The electronic circuit further comprises measuring means for measuring the torque value increase during operation of the machine with respect to angular position of the rotating drive means, second anticipating means for anticipating from saidmeasuring of the torque value increase a remaining torque value increase necessary to follow for reaching the torque reference value, computing means setting a reference angle αo and deducing from said remaining torque value increase aremaining tightening angle α from said reference angle αo to be rotated for reaching said torque reference value and means for actuating the actuating device arranged to shut off the compressed air inlet pipe after rotation of the angleα starting from said reference angle αo.
Such an arrangement allows to stop the tool at a very precise position. Effectively, if the shut off of the compressed air inlet pipe is actuated only when the reference or setting value is reached, a slight delay may occur before a completestop is attained, therefore inducing a slight overrun of said reference value.
With the above-mentioned means for measuring, anticipating, computing and controlling (with a temporisation for example) the actuating device, the shutting of the compressed air can be initiated slightly before reaching the reference value, inorder to obtain the stop of the tool very precisely at this reference value.
The portable pneumatic machine may also include elastic means wherein it further includes an elastic device arranged to slow the rotary drive means on operation therefore increasing time for reaching from a predetermined initial torque value, thetorque reference value, whereby it ameliorates tightening precision.
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