The SMART-3 S robot has an articulated structure with six motion axes and is able to carry a medium load.
The wrist can support a load of up to 6 daN at 215 mm from its centro. Its positioning repeatability is ± 0. 1 mm.
The axes are moved by brushless motors provided with emergency brakes and intenal resolvers. In axes 1, 2, and 3 motion transmission takes place by means of a Teijin reducer parallel to the motor while in axes 4, 5, and 6 Harmonic Drive reducers are used.
A bevel gear pair is used to transmit the motion on axis 5 motion transmission chain.
A counterweight is secured to the end of the arm to balance its rotations.
The robot is equipped with software, electrical and mechanical limit stops to define the axis run according to the work cycle and to ensure personnel safety.
The software limit stops are programmable. The mechanical limit stops, which are stationary, are shock absorbing pads against which the mobile parts of the robot stop.
The electrical (optional) limit stops are made up of micro-switches; when these microswitches detect the presence of suitable cams., they act so that the power to the motors is cut and the axis brake is applied.
Usually, the electrical system cuts the main power supplies whenever the electrical limit stops are reached, when motor overheating takes place, in case of particular alarm conditions or upon a manual intervention by the operator (emergency).
The mechanical group locations on the robot are shown in Fig. 1.
RPT MODULE - AXES POSITION MEASUREMENT SYSTEM (Fig. 2)
The axes position measurement system is absolute with one resolver built in the motor and one RPT (Resolver Position Tracker) absolute transduction module housed in the robot lower distribution unit.
Thanks to the one resolver measurement system, with no joint and built in the motor, less cables will be used on the robot for control System to Robot connection with a considerable increase of system reliability.
The absolute transduction function is performed by the RPT module, mounted on the robot This module energizes the transducers and reads the robot axe's position even there is no mains voltage or no connection between control System and robot and in doing so it replaces the energization signal provided by the control System.
The count of revolutions of every robot axis resolver is stored in a non-volatile way even with no mains power supply thanks to a back up battery; this makes it possible to always know the absolute position of the different machine axes.
The RPT module also contains information and characteristics about the robot on which it is installed, such as: number of axes, their electrical and mechanical characteristics as well as robot code number, allowing the control System to check for system congruity.
Fig. 2 shows the control System to Robot interconnection block diagram for axis position definition.
The drive is a sinusoidal current generator driven by a torque reference on two vectors.
According to the axis position values provided by the resolver, the control System will close both position and speed loops and will supply the drive with the torque analog reference.
Speed and position loops are stabilized by means of digital parameters definition, with no need of potentiometers calibration.
Three different conditions are typical of the RPT module operation:
The resolver energization signal sample frequency will automatically fit a possible robot movement to allow the resolver to reduce consumptions and to improve the back up battery power supply capacity to at least 1000 hours without loosing the axis position information.
RPTMODULE - BACKUP BATTERY
The RPT back up battery, housed in the robot lower distribution unit, is a lead acid, sealed and rechargeable 6V-6Ah battery.
It is provided with a recharge circuit which is enabled when the main switch on the control panel is ON and the service +24 V circuit lamp is lit.
The back up battery allows the RPT module to work even with no external power supply voltage and to retain the data for a maximum of 1000 hours; the minimum back up battery life is 4-5 years. In fact, is retains the resolver revolution count for every axis as well as a few data about the robot on which it is installed.
In order not to loose the RPT memory contents because of a back up battery malfunction, the RPT module is provided with a "battery low" control circuit. This circuit performs a check only upon control System power on; in case of battery low charge, under the minimum threshold, it stores the information. When the electronics is switched on, it warns the operator with an alarm message on the programming terminal display. After the RPT module has informed the control System about the battery status, it resets this information and does not repeat any control until the control System (not the electronics) is switched back on.
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