From: W. Trevor King <wking@drexel.edu>
Date: Thu, 31 Mar 2011 20:55:59 +0000 (-0400)
Subject: Add backlash_safe to step_relative().'
X-Git-Tag: v0.4~8
X-Git-Url: http://git.tremily.us/?a=commitdiff_plain;h=97baf5a702d603fa0c1304c459cc1263ed7c2e8f;p=stepper.git

Add backlash_safe to step_relative().'
---

diff --git a/stepper.py b/stepper.py
index 05325fe..36b52ee 100644
--- a/stepper.py
+++ b/stepper.py
@@ -212,5 +212,18 @@ class Stepper (object):
             LOG.debug('stepping %s -> %s (%s)' % (target_position, self.position, direction))
             self.single_step(direction)
 
-    def step_relative(self, relative_target_position):
-        return self.step_to(self.position + relative_target_position)
+    def step_relative(self, relative_target_position, backlash_safe=False):
+        """Step relative to the current position.
+
+        If `backlash_safe` is `True` and `relative_target_position` is
+        negative, step back an additional `.backlash` half-steps and
+        then come back to the target position.  This takes the slack
+        out of the drive chain and ensures that you actually do move
+        back to the target location.  Note that as the drive chain
+        loosens up after the motion completes, the stepper position
+        will creep forward again.
+        """
+        target = self.position + relative_target_position
+        if backlash_safe and relative_target_position < 0:
+            self.step_to(target - self.backlash)
+        self.step_to(target)