AN453_1: Connection of power drivers to TMC453

Transcription

1 TMC453 Application notes A 1 A453_1: Connection of power drivers to TMC453 This application note describes the connection power drivers to the TMC453, especially for very high microstep resolution. A very fine microstep resolution may require an elimination of the offset voltage of the TMC453. This can easily be done, using the depicted OP-AMP schematic, by slightly raising the common ground potential. When driving a standard stepper motor driver IC its maximum reference voltage for the control of the coil current has to be considered. The Allegro A3958 for example requires a VREG voltage in the range 0 to 2.6V. When realizing the depicted circuit, it is advisable to replace the 22K resistor by a value of 13K, which results in about 2.5V amplitude. When the OP-circuit is not used, in this case a voltage divider should be used on the output of the TMC, to minimize the influence of the offset voltage. To drive longer lines or multiple inputs with the analog outputs (REF_OUT, DACi_OUT) of the TMC453, a series resistor of some KOhms should be placed near the outputs of the TMC, because the internal OPs can drive only small load capacities. The control of the standby current reduction via DAC2 for 2 phase motors is not shown in the schematic, but it should be implemented to save energy and to reduce heat generation in the motor and the drivers. This is done by controlling the positive reference voltage of DAC0 and DAC1 via DAC2_OUT. Alternatively the current reduction can be controlled by the MC0 and MC1 outputs of the TMC453, because a two or three level current control is sufficient for most applications. Many power drivers have got digital current control lines for this kind of control. Otherwise the DACi_RP voltages can be reduced using an additional switchable voltage divider. The polarity of each coil driver is controlled digitally by TO0, TO2 (and TO4 ) for 2-(3-) phase motors. ote for the demonstration board: Here the GD lines are layouted badly, which results in a high noise voltage on all lines, when measuring voltages on the board. For own designs it is advisable to use a massive GD (and ) plane. REF_OUT 4V 22K REF_I TMC V 6K8 3K V 100K 100K DACi_RP DACi_R DACi_OUT 100K - + 5V Out: V 100K -5V

2 TMC453 Application notes A 2 A453_2: A complete system with an 80C51 microcontroller This application note describes the integration of the TMC 453 into a microcontroller system. The TMC453 can be directly connected to the multiplexed address-/ data bus of the 80C51. ince every read access has to be terminated by a high potential on C, the sample circuit uses an AD gate for the /WR and /RD signals. When fast 8051 derivatives are used, which are internally clocked higher than the ordinary 8051 or which work with higher clock frequencies than the TMC453, it will be necessary to introduce some waitstates, or to clock the TMC453 faster than the CPU. In every case you can control the TMC453 via port lines using programmed I/O. In many cases a 2 wire interface is completely sufficient and saves interconnections. opt. step- / direction interface 12MHz control -interface (R232 /R485 / CA o.a.) interface driver microcontroller z.b. 80c51 /RD /WR AD0..7 ALE opt. serial interface /C /OE /WE AD0..7 ALE CL DA CLK TEPI DIRI TEPOUT DIROUT stepper motor controller TMC453 CH CHB CHA REFOUT DAC2RP DAC2OUT TO4 DAC1RP DAC1OUT TO2 DAC0RP DAC0OUT TO0 MC0 MC1 I2 PH2 I1 PH1 I0 PH0 currency control motor driver 3.Ph motor driver e.g. TMC236 / TMC239 stepper motor addresslatch HC373 A8..15 A0..7 EPROM 27C512 opt. incremental encoder /PE A453_3: Position control using a simple travel switch This application note describes a simple possibility to monitor the stepper motors position using a travel switch, which is pressed frequently under normal operating conditions. The internal encoder interface of the TMC453 can even be used to detect the loss of steps, when the application does not have an incremental encoder. A loss of steps always means, that the motor position is wrong by more than 2 fullsteps. Therefore the two phase signals (pins TO0 and TO2) of a two phase motor directly drive the encoder inputs (CHA and CHB). This allows the encoder counter to count the fullsteps of the motor. ow the null channel of the encoder (CH) can be connected to the travel switch. Whenever the switch is pressed, the TMC453 can latch the value in the encoder counter automatically and can issue an interrupt, so that the CPU now can check the stored position. If it differs from the last value, the application has lost precision and the user can decide to do a new reference search.

3 TMC453 Application notes A 3 A453_4: PID control with different step resolutions of stepper / encoder This application note describes how the PID control unit works with different step resolutions concerning stepper motor and an incremental encoder connected to it. Before the PID unit is activated, motor and encoder position should match. Then the PID regulator can be enabled. The motor then is controlled by the difference between the target position, coming from the ramp generator (s. p. 45) and the encoder position (actual position). The resolution of motor and encoder can be different! In this case, the motor isn t driving with the ramp generator velocity, but with some fraction of it. Therefore, if the resolution of the encoder is higher than the motor resolution, the maximum ramp velocity has to be reduced by the same factor. The target position is still driven by the ramp generator. A453_5: Driving a 5 Phase tepper motor with the TMC453 This application note describes how to drive a 5 phase stepper motor using inexpensive standard motor drivers. To drive a 5 phase motor you can either use 5 single drivers or 3 paired drivers. The drivers need a phase input and an enable input for each coil, resulting in 10 control lines (TO0=Phase 1 and TO1=Enable 1, TO2=Phase 2 and TO3=Enable 2, etc.) driven by the TMC453. Current control can be done via the digital outputs MC0 and MC1 or via DAC2 output, programmable by user selected values. When chopped drivers are used, it may be important to synchronize their chopping frequency to avoid the generation of interference noise. uch a synchronization is described in ( High current drive using 4*JM3770A) for the JM3770 single channel driver. The following schematic shows two coils driven with the L6219, using its digital current control inputs as enable. ote that this schematic is not useful for two phase motors, since the halfstep position current is not compensated. REFOUT DAC2RP DAC2OUT DAC2R Motor Current tepper Motor Controller TMC453 TO3 TO2 TO1 TO0 DIABLE2 PHAE2 DIABLE1 PHAE1 Vref1+Vref2 I02+I12 PH2 I01+I11 PH1 L6219 Phases 1+2 of 5 Phase tepper motor Choice of drivers if a higher motor current is required: The TMC236 and TMC239 give very good results, especially it is possible to synchronize multiple drivers by using a common chopper clock. However, they do not provide an Phase Enable input, but you can use ½ 4066 analog switch to switch the DAC2 out signal to the IA and IB current control inputs. This will provide for an inverted enable input.

4 TMC453 Application notes A 4 A453_6: Dynamic switching to fullstep operation In some cases the user might want to operate the motor in full-step instead of microstep mode whenever the step frequency exceeds some threshold. MC0/MC1 (v>x) REFOUT TMC453 DAC1 DAC1RP DAC0 DAC0RP TO1 TO0 74HC4053 I2 I1 PH2 PH1 motor driver stepper motor This diagram shows how the TMC453 should be connected to the stepper motor driver, in order to allow a dynamic switching to full step mode. Function: In normal microstep operation DAC0OUT and DAC1OUT provide the two input signals (I0 and I1) of the motor driver. If the frequency is higher than a previously set limit, the 74HC4053 switches I0 and I1 directly to the REFOUT output of the TMC453. In this case the motor is driven in full-stepping mode, instead of micro-stepping-mode. Advantage: In full-stepping mode the motor has a slightly higher torque and the disadvantages of fullstepping (noise and vibrations) recede with an increasing stepping frequency. A453_7: Programmable ramps This application note describes how to use the TMC453 s programmable ramp segments. In some applications the motor s target position might change, while the ramp is driven. ince the internal ramp algorithm does not allow this, the user might want to use the ramp segments to accomplish this. While the target position is not found it is simple: If the position difference is positive, a constant ramp is driven with positive acceleration in order to reach vmax, otherwise, if the difference is negative, the ramp is driven with negative acceleration in order to reach -vmax. The same applies for parabolic parts (s-shape). OW, in order to stop at the target position it is necessary to know the actual position and to decide whether it is time to slow down the velocity. For linear ramps the calculation is easy: The distance s to the position in which the motor slows down to 0 is proportional the square of the velocity: 2 fifo _ v _ nom s = 128 ramp _ actaccel Once the remaining distance is near the calculated number of steps for slow down, the slow down phase is started (not to zero, but to a minimum velocity vmin which allows to stop the motor at once). The last part of the ramp is driven with vmin, and the stop event is triggered at the target position. The actual number of steps may differ from the calculated s, because of the unknown start value of the pulse generator. This is especially the case for low starting velocities or for low values of ramp_actaccel. For short moves use the above formula to calculate fifo_v_nom for the move to reach the target with a triangular ramp. Including parabolic ramps works analog, but needs more calculations or a set of tables. The event triggered FIFO of the TMC453 ideally supports this kind of ramp programming. Keep in mind, that all operation modes remain active, until the next FIFO command is executed. Thus, the motor does not stop when the FIFO is empty!

5 TMC453 Application notes A 5 A453_8: ynchronizing the motor to an external clock signal This application note describes motion control when an external ramp clock source is used. The TMC453 supports three different sources to drive the motor (TRIGGER TYPE, see page 35): The first is the internal ramp generator, the second is the step-/dir input or CHA/CHB as step-/dir and the third is the quadrature encoder input. If an other source than the ramp generator is chosen, the complete ramp generation logic is bypassed - this means that the ramp generator logic is not used. If an external enable signal is required, an external AD-gate (or two for quadrature signals) have to be used. When synchronizing movement to a fixed external clock, like an encoder signal, have in mind that the stepper motor always needs a smooth start ramp, except for very low velocities. To accomplish this, you could use the TMC453 ramp generator to accelerate to roughly the input signal velocity, before switching to encoder input. The TMC453 has internal logic that can measure quadrature encoder velocity. The other possibility to slowly increase motor velocity is, to start with a high gearing value, and to decrease it until the desired value is reached. Please note, that this may not work for low values like 1:1, since the step 1:2 to 1:1 is too large. A453_9: Problems when driving low distances with the automatic ramp This note describes how to speed up positioning when very low position differences are driven in alternating directions. In some applications very low positioning speeds may occur, when distances of less than 15 microsteps are driven in automatic ramp mode, following a change of direction. This is due to heuristical calculations in the ramp generator. To avoid this, do the following: When the distance to the next target position is between 2 and 15 steps, and a change of the direction has occurred after the previous movement, drive the first step using a separate automatic ramp command. Drive the remaining 1 to 14 steps afterwards. A453_10: Problems when changing the sine step resolution several times This application note describes, how to switch between two step resolutions using the sine generator, if the application requires it. This problem occurs, because the sine generator works with discrete values and the range of this values depends on the resolution. Therefore, it can happen that the amplitude rises a bit or goes down a bit on changing the resolution. ow, when the switching is done multiple times, this failure accumulates and results in decreased accuracy and in the end can cause a deadlock. In order to avoid this, the amplitudes for sine and cosine waves should be held on a constant level (i.e. sinvalue^2 + cosvaluet^2 = constant) after each switching of the resolution (or each second time). It is simpler when motor is stopped at a known microstep position, e.g. the null position, since then constants can be used for initialization. A453_11: Using the TMC453 step-/direction signals to drive power modules This application note describes how to match the TMC453 step-/ direction outputs to external motor power driver modules. Power driver modules available from different manufacturers require different input timings. Especially the direction switching delay may be critical (setup time, until the next step impulse can be received). This problem does not occur, when a CW-/ CCW pulse interface is used, because there is no critical time relationship between both signals. The TMC453 output signals can be converted to CW-/ CCW impulses using some discrete logic.

6 TMC453 Application notes A 6 If a CW-/ CCW- interface is not available for a particular driver module, some more complex logic might be required to satisfy the driver s requirements. The following schematic shows a simple means to generate a direction setup time of up to near the delay between two pulses at maximum step frequency. 100p R2 74HC123 CX RCX 100p R1 74HC123 CX RCX TEP TEP_OUT B /A B /A /RE /RE TMC453 74HC74 CLK /PRE DIR DIR_OUT D /CLR Dir change to Pulse delay td1 <= 1 / ftepmax recommended: * td2 R2 = td1 / (0.45 * 100pF) Direction signal register Pulse length generation td2 = 1/2 * 1 / ftepmax R2 = td2 / (0.45 * 100pF) An solution to provide for a longer direction signal setup time is described in the following: In order to have the driving direction (DIR) available in time before the first step impulse comes, the YC_OUT-pin can be used instead of the DIR output. This pin then has to be programmed with the FIFO commands. The internal timer commands make it possible to match the power driver timing. ote that YC_OUT then has to be programmed with the sign of the direction in each FIFOcommand. A453_12: Converting the acceleration values to physical units While the step frequency is described in the data sheet, there is no formula for linear acceleration in steps/second^2. When driving linear ramps, the acceleration can be calculated as follows: a = f 2 clk ramp _ actaccel fifo _ pre _ div This formula refers to the step pulses, resp. the microstep resolution used. Divide this value by the number of microsteps, to get the result in Fullsteps/second^2 [1/s²]. A453_13: Using the TMC453 with multi axis interpolation How can the TMC453 be used to drive a roboter requiring multi axis interpolation? To get the axis running synchronized, you can trigger the commands via the YC_I input, e.g. by connecting it to a port pin, or by connecting it to the YC_OUT of an other TMC453, which acts as master. To get the axis running synchronously, you can work with linear ramps, by programming the acceleration and velocity values according to the slope of the actual straight line. ow, to overcome the limited resolution of 14 bit, i.e. about +/-0.01 percent accuracy, you just cut the lines into segments of a about 100 (micro)steps, which gives you a maximum deviation of a one (micro)step. The TMC453 also allows latching of the actual position values when you trigger a command. o whenever you start the next line segment, you can readout the actual values to calculate the succeeding segment. This

7 TMC453 Application notes A 7 queueing gives you one line segment of time for calculations. The faster your processor, the more exact the result. A453_14: Programming the TMC453 to drive a three phase stepper This application note describes how to program the TMC453 to output 3 sinewaves and polarity signals with a 120 degree phase shift for a 3 phase stepper motor. To operate a 3 phase motor, the RAM table has to be used. For example for 8 microsteps do the following: 1. PhaseGen_O = 0 2. Program a half sine wave with 12 entries into the memory, starting from address 0, then set mstep_table_end = 12-1, mstep_full_step_dist = 4-1, 3. et the phase pointers with a 120 degree shift, i.e. to: mstep_phase0_cnt=0, mstep_phase1_cnt=8, mstep_phase2_cnt=4. The sequencer has to be programmed with pattern " ": 4. teptype = Microstep, MotorType = 3 phase, et_auto_phase_index = 1 (other bits: 0): seq_config=$ eq_phase_pattern=" " 6. PhaseGen_O = 1 (all other bits as at tep 4.): seq_config=$0289 ow you can operate the TMC453. The sine waves are output by the DACs, the polarities come via pins TO0, TO2 and TO4. A453_15: Range for bow an acceleration values In order to always get a stable bow and acceleration behaviour, some some limits for the setting of the bow and anom values should be observed. ince the integrators in the ramp generator uses 1/256 of bow value to increase the acceleration until a_nom is reached, and 1/256 of acceleration (a_nom) to increase the velocity until v_nom is reached, it makes sense to set a_nom <= 256 * v_nom bow <= 256 * a_nom This is mandatory for the automatic ramp to work. If these rules are violated, the velocity or acceleration value will not increase at all! For a reasonable setting, the values should be chosen in a way, that the maximum velocity / acceleration values can be reached exactly. Therefore, the setting should fulfill the following: (a_nom <= 256 * v_nom) OR (a_nom = 256 * v_nom / n n : integer <= v_nom * 256) (bow <= 256 * a_nom) OR (bow = 256 * a_nom / n n : integer <= a_nom * 256) Both possibilities allow the integrators to reach the full specified maximum values : In the first case, the velocity respectively the acceleration values are increased in increments of one. In the second case, the increment is an integer divider of the value to be reached. The reason for this is, that the acceleration and velocity integrators stop operation, whenever the next addition would exceed the limiting values.

8 TMC453 Application notes A 8 A453_16: Maximizing bow phase impact In order to take advantage of the bow phase, the bow phase should not be too short. In the TMC453 there is a tradeoff between bow phase duration and microstep resolution. When understanding the TMC453 ramp generator, it becomes clear, that the bow phase just accounts for a very small part of the acceleration phase, if the acceleration value itself is very low. Thus, the acceleration values should be far away from 1. However, the acceleration setting depends on the predivider setting: A high microstep resolution requires a fast stepping rate. On the other hand, this increases ramp generator frequency, and thus you need to reduce acceleration and bow values. Following pictures show the bow with different parameters. Here the acceleration value is high, so that the bow takes a great effect. What can be done, to get a high acceleration value, yielding a longer bow phase? In the TMC453 there is a trade-off between the number of microsteps and the resolution of the acceleration. This is due to both, ramp generator and pulse generator use the same time base. o, the only means to get to a better acceleration resolution is reducing the number of microsteps and at the same time increasing the pre-divider value, thus, giving a lower operation frequency for the ramp generator steps ramp distance, 64 µsteps, v_max = 5159, a_max = 130 and a variable bow. Pre-divider was set to 2. Bow: 3 Bow: 10